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Android is an operating system based on Linux with a Java programming interface.The Android Software Development Kit (Android SDK) provides all necessary tools to develop Android applications. This includes a compiler, debugger and a device emulator, as well as its own virtual machine to run Android programs.Android is currently primarily developed by Google.Android allows background processing, provides a rich user interface library, supports 2-D and 3-D graphics using the OpenGL libraries, access to the file system and provides an embedded SQLite database.Android applications consist of different components and can re-use components of other applications. This leads to the concept of a task in Android; an application can re-use other Android components to archive a task. For example you can trigger from your application another application which has itself registered with the Android system to handle photos. In this other application you select a photo and return to your application to use the selected photo.
Based on Android 4.1
Version 10.9
Copyright © 2009, 2010, 2011, 2012 Lars Vogel
21.11.2012
| Revision History | |||
|---|---|---|---|
| Revision 0.1 | 04.07.2009 | Lars Vogel | Created |
| Revision 0.2 - 10.9 | 07.07.2009 - 21.11.2012 | bug fixing and enhancements | |
Table of Contents
- 1. What is Android?
- 2. Basic Android User Interface components
- 3. Other Android components
- 4. Android Development Tools
- 5. Android Application Architecture
- 6. Resources
- 7. Using Resources
- 8. Installation
- 9. Android virtual device - Emulator
- 10. Tutorial: Create and run Android Virtual Device
- 11. Solving Android development problems
- 12. Conventions for the tutorials
- 13. Tutorial: Your first Android project
- 14. Starting an installed application
- 15. Layout Manager and ViewGroups
- 16. Tutorial: ScrollView
- 17. Fragments
- 18. Fragments Tutorial
- 19. Fragments Tutorial - layout for portrait mode
- 20. OptionMenu and ActionBar
- 21. Advanced ActionBar
- 22. Tutorial: ActionBar
- 23. Tutorial: Using the contextual action mode
- 24. ActionBar navigation with Fragments
- 25. DDMS perspective and important views
- 26. Deployment
- 27. Thank you
- 28. Questions and Discussion
- 29. Links and Literature
Android is an operating system based on Linux with a Java programming interface.
The Android Software Development Kit (Android SDK) provides all necessary tools to develop Android applications. This includes a compiler, debugger and a device emulator, as well as its own virtual machine to run Android programs.
Android is currently primarily developed by Google.
Android allows background processing, provides a rich user interface library, supports 2-D and 3-D graphics using the OpenGL libraries, access to the file system and provides an embedded SQLite database.
Android applications consist of different components and can re-use components of other applications. This leads to the concept of a task in Android; an application can re-use other Android components to archive a task. For example you can trigger from your application another application which has itself registered with the Android system to handle photos. In this other application you select a photo and return to your application to use the selected photo.
The Android Software Development Kit (Android SDK) provides all necessary tools to develop Android applications. This includes a compiler, debugger and a device emulator, as well as its own virtual machine to run Android programs.
Android is currently primarily developed by Google.
Android allows background processing, provides a rich user interface library, supports 2-D and 3-D graphics using the OpenGL libraries, access to the file system and provides an embedded SQLite database.
Android applications consist of different components and can re-use components of other applications. This leads to the concept of a task in Android; an application can re-use other Android components to archive a task. For example you can trigger from your application another application which has itself registered with the Android system to handle photos. In this other application you select a photo and return to your application to use the selected photo.
Google offers the Google Play service in which programmers can offer their Android application to Android users. Google phones include the Google Play application which allows to install applications.
Google Play also offers an update service, e.g. if a programmer uploads a new version of his application to Google Play, this service will notify existing users that an update is available and allow to install it.
Google Play used to be called Android Market.
Google Play also offers an update service, e.g. if a programmer uploads a new version of his application to Google Play, this service will notify existing users that an update is available and allow to install it.
Google Play used to be called Android Market.
During deployment on an Android device, the Android system will create a unique user and group ID for every Android application. Each application file is private to this generated user, e.g. other applications cannot access these files.
In addition each Android application will be started in its own process.
Therefore by means of the underlying Linux operating system, every Android application is isolated from other running applications.
If data should be shared, the application must do this explicitly, e.g. via a Service or a ContentProvider.
Android also contains a permission system. Android predefines permissions for certain tasks but every application can define additional permissions.
An Android application declare its required permissions in its
Permissions have different levels. Some permissions are automatically granted by the Android system, some are automatically rejected.
In most cases the requested permissions will be presented to the user before installation of the application. The user needs to decide if these permissions are given to the application.
If the user denies a permission required by the application, this application cannot be installed. The check of the permission is only performed during installation, permissions cannot be denied or granted after the installation.
Not all users pay attention to the required permissions during installation. But some users do and they write negative reviews on Google Play.
In addition each Android application will be started in its own process.
Therefore by means of the underlying Linux operating system, every Android application is isolated from other running applications.
If data should be shared, the application must do this explicitly, e.g. via a Service or a ContentProvider.
Android also contains a permission system. Android predefines permissions for certain tasks but every application can define additional permissions.
An Android application declare its required permissions in its
AndroidManifest.xml configuration file. For example an application may declare that it requires access to the Internet. Permissions have different levels. Some permissions are automatically granted by the Android system, some are automatically rejected.
In most cases the requested permissions will be presented to the user before installation of the application. The user needs to decide if these permissions are given to the application.
If the user denies a permission required by the application, this application cannot be installed. The check of the permission is only performed during installation, permissions cannot be denied or granted after the installation.
Not all users pay attention to the required permissions during installation. But some users do and they write negative reviews on Google Play.
The following gives a short overview of the most important user interface components in Android.
An Activity represents the visual representation of an Android application. Activities use Views and Fragments to create the user interface and to interact with the user.
An Android application can have several Activities.
An Android application can have several Activities.
Fragments are components which run in the context of an
Fragments are optional, you can use Views and ViewGroups directly in an Activity but in professional applications you always use them to allow the reuse of your user interface components on different sized devices.
Activity. Fragment components encapsulate application code so that it is easier to reuse it and to support different sized devices. Fragments are optional, you can use Views and ViewGroups directly in an Activity but in professional applications you always use them to allow the reuse of your user interface components on different sized devices.
Views are user interface widgets, e.g. buttons or text fields. The base class for all Views is the
A ViewGroup is responsible for arranging other Views. ViewGroups is also called layout managers. The base class for these layout managers is the
android.view.View class. Views have attributes which can be used to configure their appearance and behavior. A ViewGroup is responsible for arranging other Views. ViewGroups is also called layout managers. The base class for these layout managers is the
android.view.ViewGroup class which extends the View class. ViewGroups can be nestled to create complex layouts. You should not nestle ViewGroups too deeply as this has a negative impact on the performance.
Activities are defined with different layouts. These layouts can be picked based on several different factoring including the size of the actual device.
The following picture shows an Activity called MainActivity. On a wide screen it shows two Fragments. On a smaller screen it shows one Fragment and allows that the user navigate to another Activity called SecondActivity which displays the second Fragment.
The following picture shows an Activity called MainActivity. On a wide screen it shows two Fragments. On a smaller screen it shows one Fragment and allows that the user navigate to another Activity called SecondActivity which displays the second Fragment.
Android has several more components which can be used in your Android application.
Intents are asynchronous messages which allow the application to request functionality from other components of the Android system, e.g. from Services or Activities. An application can call a component directly (explicit Intent) or ask the Android system to evaluate registered components based on the Intent data (implicit Intents ). For example the application could implement sharing of data via an
Intents allow to combine loosely coupled components to perform certain tasks.
Intent and all components which allow sharing of data would be available for the user to select. Applications register themselves to an Intent via an IntentFilter. Intents allow to combine loosely coupled components to perform certain tasks.
Services perform background tasks without providing a user interface. They can notify the user via the notification framework in Android.
A ContentProvider provides a structured interface to application data. Via a ContentProvider your application can share data with other applications. Android contains an SQLite database which is frequently used in conjunction with a ContentProvider. The SQLite database would store the data, which would be accessed via the ContentProvider.
BroadcastReceiver can be registered to receive system messages and Intents. A BroadcastReceiver will get notified by the Android system, if the specified situation happens. For example a BroadcastReceiver could get called once the Android system completed the boot process or if a phone call is received.
Widgets are interactive components which are primarily used on the Android homescreen. They typically display some kind of data and allow the user to perform actions via them. For example a Widget could display a short summary of new emails and if the user selects an email, it could start the email application with the selected email.
Android provide many more components but the list above describes the most important ones. Other Android components are Live Folders and Live Wallpapers . Live Folders display data on the homescreen without launching the corresponding application while Live Wallpapers allow to create animated backgrounds.
The Android Software Development Kit (SDK) contains the necessary tools to create, compile and package Android application. Most of these tools are command line based.
The Android SDK also provides an Android device emulator, so that Android applications can be tested without a real Android phone. You can create Android virtual devices (AVD) via the Android SDK, which run in this emulator.
The Android SDK contains the Android debug bridge (adb) tool which allows to connect to an virtual or real Android device.
The Android SDK also provides an Android device emulator, so that Android applications can be tested without a real Android phone. You can create Android virtual devices (AVD) via the Android SDK, which run in this emulator.
The Android SDK contains the Android debug bridge (adb) tool which allows to connect to an virtual or real Android device.
Google provides the Android Development Tools (ADT) to develop Android applications with Eclipse. ADT is a set of components (plug-ins) which extend the Eclipse IDE with Android development capabilities.
ADT contains all required functionalities to create, compile, debug and deploy Android applications from the Eclipse IDE. ADT also allows to create and start AVDs.
The Android Development Tools (ADT) provides specialized editors for resources files, e.g. layout files. These editors allow to switch between the XML representation of the file and a richer user interface via tabs on the bottom of the editor.
ADT contains all required functionalities to create, compile, debug and deploy Android applications from the Eclipse IDE. ADT also allows to create and start AVDs.
The Android Development Tools (ADT) provides specialized editors for resources files, e.g. layout files. These editors allow to switch between the XML representation of the file and a richer user interface via tabs on the bottom of the editor.
The Android system uses a special virtual machine, i.e. the Dalvik Virtual Machine to run Java based applications. Dalvik uses an own bytecode format which is different from Java bytecode.
Therefore you cannot directly run Java class files on Android, they need to get converted in the Dalvik bytecode format.
Therefore you cannot directly run Java class files on Android, they need to get converted in the Dalvik bytecode format.
Android applications are primarily written in the Java programming language. The Java source files are converted to Java class files by the Java compiler.
The Android SDK contains a tool called dx which converts Java class files into a
These dex files are therefore much smaller in size than the corresponding class files.
The
The resulting
The Android Development Tools (ADT) performs these steps transparently to the user.
If you use the ADT tooling you press a button the whole Android application (
The Android SDK contains a tool called dx which converts Java class files into a
.dex (Dalvik Executable) file. All class files of one application are placed in one compressed .dex file. During this conversion process redundant information in the class files are optimized in the .dex file. For example if the same String is found in different class files, the .dex file contains only once reference of this String. These dex files are therefore much smaller in size than the corresponding class files.
The
.dex file and the resources of an Android project, e.g. the images and XML files, are packed into an .apk (Android Package) file. The program aapt (Android Asset Packaging Tool) performs this packaging. The resulting
.apk file contains all necessary data to run the Android application and can be deployed to an Android device via the adb tool. The Android Development Tools (ADT) performs these steps transparently to the user.
If you use the ADT tooling you press a button the whole Android application (
.apk file) will be created and deployed.
The ADT allows the developer to define certain artifacts, e.g. Strings and layout files, in two ways: via a rich editor, and directly via XML. This is done via multi-page editors in Eclipse. In these editors you can switch between both representations by clicking on the tab on the lower part of the screen.
For example if you open the
For example if you open the
res/layout/main.xml file in the Package Explorer View of Eclipse, you can switch between the two representations as depicted in the following screenshot.
The components and settings of an Android application are described in the
It must also contain the required permissions for the application. For example if the application requires network access it must be specified here.
AndroidManifest.xml file. For example all Activities and Services of the application must be declared in this file. It must also contain the required permissions for the application. For example if the application requires network access it must be specified here.
xmlns:android="http://schemas.android.com/apk/res/android"
package="de.vogella.android.temperature"
android:versionCode="1"
android:versionName="1.0">
android:icon="@drawable/icon" android:label="@string/app_name">
android:name=".Convert"
android:label="@string/app_name">
android:name="android.intent.action.MAIN" />
android:name="android.intent.category.LAUNCHER" />
The
package attribute defines the base package for the Java objects referred to in this file. If a Java object lies within a different package, it must be declared with the full qualified package name. Google Play requires that every Android application uses its own unique package. Therefore it is a good habit to use your reverse domain name as package name. This will avoid collisions with other Android applications.
android:versionName and android:versionCode specify the version of your application. versionName is what the user sees and can be any String. versionCode must be an integer. The Android Market determine based on the versionCode, if it should perform an update of the applications for the existing installations. You typically start with "1" and increase this value by one, if you roll-out a new version of your application. The
tag defines an Activity, in this example pointing to the Convert class in the de.vogella.android.temperature package. An intent filter is registered for this class which defines that this Activity is started once the application starts (action android:name="android.intent.action.MAIN" ). The category definition category android:name="android.intent.category.LAUNCHER" defines that this application is added to the application directory on the Android device. The
@string/app_name value refers to resource files which contain the actual value of the application name. The usage of resource file makes it easy to provide different resources, e.g. strings, colors, icons, for different devices and makes it easy to translate applications. The
uses-sdk part of the AndroidManifest.xml file defines the minimal SDK version for which your application is valid. This will prevent your application being installed on unsupported devices.
The Android system controls the lifecycle of your application. At any time the Android system may stop or destroy your application, e.g. because of an incoming call. The Android system defines a lifecycle for Activities via predefined methods. The most important methods are:
-
onSaveInstanceState()- called after theActivityis stopped. Used to save data so that theActivitycan restore its states if re-started
-
onPause()- always called if theActivityends, can be used to release resource or save data
-
onResume()- called if theActivityis re-started, can be used to initialize fields
An
In the emulator you can simulate the change of the orientation via Ctrl+F11.
You can avoid a restart of your application for certain configuration changes via the
Activity will also be restarted, if a so called "configuration change" happens. A configuration change happens if an event is triggered which may be relevant for the application. For example if the user changes the orientation of the device (vertically or horizontally). Android assumes that an Activity might want to use different resources for these orientations and restarts the Activity. In the emulator you can simulate the change of the orientation via Ctrl+F11.
You can avoid a restart of your application for certain configuration changes via the
configChanges attribute on your Activity definition in your AndroidManifest.xml. The following Activity will not be restarted in case of orientation changes or position of the physical keyboard (hidden / visible). android:name=".ProgressTestActivity"
android:label="@string/app_name"
android:configChanges="orientation|keyboardHidden|keyboard">
The class
The Context also provides access to Android Services, e.g. the Location Service.
Activities and Services extend the
android.content.Context provides the connection to the Android system and the resources of the project. It is the interface to global information about the application environment. The Context also provides access to Android Services, e.g. the Location Service.
Activities and Services extend the
Context class.
Android supports that resources, like images and certain XML configuration files, can be keep separate from the source code.
These resources must be defined in the
The following table give an overview of the supported resources and their standard folder prefix.
The
If you create a new resource, the corresponding reference is automatically created in
The Android system provides methods to access the corresponding resource via these IDs.
For example to access a String with the
These resources must be defined in the
res directory in a special folder dependent on their purpose. You can also append additional qualifiers to the folder name to indicate that the related resources should be used for special configurations, e.g. you can specify that a resource is only valid for a certain screen size. The following table give an overview of the supported resources and their standard folder prefix.
Table 1. Resources
| Resource | Folder | Description |
|---|---|---|
| Simple Values | /res/values | Used to define strings, colors, dimensions, styles and static arrays of strings or integers. By convention each type is stored in a separate file, e.g. strings are defined in the res/values/strings.xml file. |
| Layouts | /res/values | XML file with layout description files used to define the user interface for Activities and Fragments. |
| Styles and Themes | /res/values | Files which define the appearance of your Android application. |
| Animations | /res/animator | Define animations in XML for the property animation API which allows to animate arbitrary properties of objects over time. |
| Menus | /res/menu | Define the properties of entries for a menu. |
The
gen directory in an Android project contains generated values. R.java is a generated class which contains references to certain resources of the project. If you create a new resource, the corresponding reference is automatically created in
R.java via the Eclipse ADT tools. These references are static integer values and define IDs for the resources. The Android system provides methods to access the corresponding resource via these IDs.
For example to access a String with the
R.string.yourString ID, you would use the getString(R.string.yourString)) method. R.java is automatically created by the Eclipse development environment, manual changes are not necessary and will be overridden by the tooling.
While the
res directory contains structured values which are known to the Android platform, the assets directory can be used to store any kind of data. You access this data via the AssetsManager which you can access the getAssets() method. AssetsManager allows to read an assets as InputStream with the open() method. // Get the AssetManager AssetManager manager = getAssets(); // Read a Bitmap from Assets try { InputStream open = manager.open("logo.png"); Bitmap bitmap = BitmapFactory.decodeStream(open); // Assign the bitmap to an ImageView in this layout ImageView view = (ImageView) findViewById(R.id.imageView1); view.setImageBitmap(bitmap); } catch (IOException e) { e.printStackTrace(); }
The
Resources class allows to access individual resources. An instance of Resources can get access via the getResources() method of the Context class. Resources is also used by other Android classes, for example the following code shows how to create a Bitmap file from a reference ID. BitmapFactory.decodeResource(getResources(), R.drawable.ic_action_search);
In your XML files, for example your layout files, you can refer to other resources via the
For example, if you want to refer to a color which is defined in a XML resource, you can refer to it via
@ sign. For example, if you want to refer to a color which is defined in a XML resource, you can refer to it via
@color/your_id. Or if you defined a "hello" string in an XML resource, you could access it via @string/hello.
The user interface for Activities is defined via layouts. The layout defines the included
A layout can be defined via Java code or via XML. In most cases the layout is defined as an XML file.
XML based layouts are defined via a resource file in the
If a
By conversion this will create and assign a new
Defining layouts via XML is usually the preferred way as this separates the programming logic from the layout definition. It also allows the definition of different layouts for different devices. You can also mix both approaches.
Views (widgets) and their properties. A layout can be defined via Java code or via XML. In most cases the layout is defined as an XML file.
XML based layouts are defined via a resource file in the
/res/layout folder. This file specifies the ViewGroups, Views, their relationship and their attributes for this specific layout. If a
View needs to be accessed via Java code, you have to give the View a unique ID via the android:id attribute. To assign a new ID to a View use @+id/yourvalue . The following shows an example in which a Button gets the button1 ID assigned. By conversion this will create and assign a new
yourvalue ID to the corresponding View. In your Java code you can later access a View via the method findViewById(R.id.yourvalue). Defining layouts via XML is usually the preferred way as this separates the programming logic from the layout definition. It also allows the definition of different layouts for different devices. You can also mix both approaches.
You have different options to install the Android development tools. The simplest way is to download a full packaged pre-configured Eclipse.
For other options please see Android installation
For other options please see Android installation
Google provides a pre-packaged and configured Eclipse based Android development environment. The following link allows to download a archive file which includes all required tools for Android development.
http://developer.android.com/sdk/index.htmlExtract the zip file and start Eclipse from the
eclipse folder via the eclipse native launcher, e.g. eclipse.exe under Windows.
The Android Development Tools (ADT) include an emulator to run an Android system. The emulator behaves like a real Android device (in most cases) and allows you to test your application without having a real device.
You can configure the version of the Android system you would like to run, the size of the SD card, the screen resolution and other relevant settings. You can define several of them with different configurations.
These devices are called Android Virtual Device and you can start several in parallel.
You can configure the version of the Android system you would like to run, the size of the SD card, the screen resolution and other relevant settings. You can define several of them with different configurations.
These devices are called Android Virtual Device and you can start several in parallel.
During the creation of an AVD you decide if you want an Android device or a Google device.
An AVD created for Android will contain the programs from the Android Open Source Project. An AVD created for the Google API's will also contain several Google applications, most notable the Google Maps application.
If you want to use functionality which is only provided via the Google API's, e.g. Google Maps you must run this application on an AVD with Google API's.
An AVD created for Android will contain the programs from the Android Open Source Project. An AVD created for the Google API's will also contain several Google applications, most notable the Google Maps application.
If you want to use functionality which is only provided via the Google API's, e.g. Google Maps you must run this application on an AVD with Google API's.
The following shortcuts are useful for working with the emulator.
Alt+Enter Maximizes the emulator. Nice for demos.
Ctrl+F11 changes the orientation of the emulator.
F8 Turns network on / off.
Alt+Enter Maximizes the emulator. Nice for demos.
Ctrl+F11 changes the orientation of the emulator.
F8 Turns network on / off.
The graphics of the emulator can use the native GPU of the computer. This makes the rendering in the emulator very fast. To enable this, add the
You can also set the
Android devices do not have to have hardware button. If you want to create such an AVD, add the
GPU Emulation property to the device configuration and set it to true. You can also set the
Enabled flag for Snapshots. This will save the state of the emulator and will let it start much faster. Unfortunately currently native GPU rendering and Snapshots do not work together. Android devices do not have to have hardware button. If you want to create such an AVD, add the
Hardware Back/Home keys property to the device configuration and set it to false.
To define an Android Virtual Device (ADV) open the AVD Manager dialog via → and press button.
Enter the values similar to the following screenshot.
Select the Enabled for Snapshots box. This will make the second start of the virtual device much faster. Afterwards press the button. This will create the AVD configuration and display it under the Virtual devices.
To test if your setup is correct, select your your new entry and press the button
After some time your AVD starts. Do not interrupt this startup process, as this might corrupt the AVD.
After the AVD started, you can use the AVD via the mouse and via the virtual keyboard of the emulator.
Enter the values similar to the following screenshot.
Select the Enabled for Snapshots box. This will make the second start of the virtual device much faster. Afterwards press the button. This will create the AVD configuration and display it under the Virtual devices.
To test if your setup is correct, select your your new entry and press the button
After some time your AVD starts. Do not interrupt this startup process, as this might corrupt the AVD.
After the AVD started, you can use the AVD via the mouse and via the virtual keyboard of the emulator.
Things are not always working as they should. You find a list of typical Android development problems and their solution under the following link: Solutions for common Android development problems .
The tutorials of this document have been developed and tested with Android 4.1, API Level 16. Please use this version for all tutorials in this tutorial. Higher versions of the API level should also work. A lower version of the Android API might also work, but if you face issues, try the recommended version.
The base package for the projects is always the same as the project name, e.g. if you are asked to create a project called de.vogella.android.example.test, then the corresponding package name is de.vogella.android.example.test.
The application name, which must be entered on the Android project generation wizard, will not be predefined. Choose a name you like.
The base package for the projects is always the same as the project name, e.g. if you are asked to create a project called de.vogella.android.example.test, then the corresponding package name is de.vogella.android.example.test.
The application name, which must be entered on the Android project generation wizard, will not be predefined. Choose a name you like.
The Android development tools show warnings, if you use hard-coded strings, for example in layout files. For real applications you should use String resource files. To simplify the creation of the examples, we use Strings directly. Please ignore the corresponding warnings.
This application is also available on the Android Marketplace under Android Temperature converter .
Alternatively you can also scan the following barcode with your Android smartphone to install it via the Google Play application.
Alternatively you can also scan the following barcode with your Android smartphone to install it via the Google Play application.
Select → → → → to create a new Android project.
Use Temperature Converter as Application name and de.vogella.android.temperature as project and package name.Select the latest Android SDK as Build SDK and
The next screen allow you to create a Launcher Icon for your application. Accept the defaults and press the button.
Select the BlankActivity template and press the button.
On the next dialog change Title attribute to Temperature Converter. Leave the rest as is.
Press the Finish button. The wizard may prompt you to install the Support library. If you are prompted, select to install it.
After the wizard finshes the following project should be created.
Use Temperature Converter as Application name and de.vogella.android.temperature as project and package name.Select the latest Android SDK as Build SDK and
API 14 as Minimum Required SDK. After entering this data, press the button. The next screen allow you to create a Launcher Icon for your application. Accept the defaults and press the button.
Select the BlankActivity template and press the button.
On the next dialog change Title attribute to Temperature Converter. Leave the rest as is.
Press the Finish button. The wizard may prompt you to install the Support library. If you are prompted, select to install it.
After the wizard finshes the following project should be created.
Android allows you to create static attributes, e.g. Strings or colors. These attributes can for example be used in your XML layout files or referred to via Java source code.
Select the
Select the Color entry in the following dialog and press the button. Enter
Add more attributes, this time of the
Switch to the XML representation and validate that the values are correct.
Select the
res/values/string.xml file and press the button. Select the Color entry in the following dialog and press the button. Enter
myColor as the name and #F5F5F5 as the value. Add more attributes, this time of the
String type. String attributes allow the developer to translate the application at a later point. Switch to the XML representation and validate that the values are correct.
name="app_name">Temparature Convertor name="hello_world">Hello world! name="menu_settings">Settings name="title_activity_main">Temparature Convertor name="myColor">#3399CC name="celsius" >to Celsius name="fahrenheit">to Fahrenheit name="calc">Calculate
Select the
The following shows a screenshot of the Palette side of this editor. from which you can drag and drop new user interface components into your layout. Please note that the Palette view changes frequently so your view might be a bit different.
You will now create the layout for your Android application.
Right-click on the existing Hello World! text object in the layout. Select from the popup menu to remove the text object.
Afterwards select the Text Fields section in the Palette and locate the Plain Text (via the tooltip).
All entries in the Text Fields section define text fields. The different entries define additional attribute for them, e.g. if a text field should only contain numbers.
Drag this onto the layout to create a text input field.
Afterwards select the Form Widgets section in the Palette and drag a RadioGroup entry into the layout. The number of radio buttons added to the radio button group depends on your version of Eclipse. Make sure there are two radio buttons by deleting or adding radio buttons to the group.
Drag a Button from the Form Widgets section into the layout.
The result should look like the following screenshot.
Switch to the XML tab of your layout file and verify that the file looks similar to the following listing. ADT changes the templates very fast, so your XML might look slighty different.
res/layout/activity_main.xml file and open the Android editor via a double-click. This editor allows you to create the layout via drag and drop or via the XML source code. You can switch between both representations via the tabs at the bottom of the editor. For changing the position and grouping elements you can use the Eclipse Outline View. The following shows a screenshot of the Palette side of this editor. from which you can drag and drop new user interface components into your layout. Please note that the Palette view changes frequently so your view might be a bit different.
You will now create the layout for your Android application.
Right-click on the existing Hello World! text object in the layout. Select from the popup menu to remove the text object.
Afterwards select the Text Fields section in the Palette and locate the Plain Text (via the tooltip).
All entries in the Text Fields section define text fields. The different entries define additional attribute for them, e.g. if a text field should only contain numbers.
Drag this onto the layout to create a text input field.
Afterwards select the Form Widgets section in the Palette and drag a RadioGroup entry into the layout. The number of radio buttons added to the radio button group depends on your version of Eclipse. Make sure there are two radio buttons by deleting or adding radio buttons to the group.
Drag a Button from the Form Widgets section into the layout.
The result should look like the following screenshot.
Switch to the XML tab of your layout file and verify that the file looks similar to the following listing. ADT changes the templates very fast, so your XML might look slighty different.
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >
android:id="@+id/editText1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:ems="10" >
android:id="@+id/radioGroup1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="@+id/editText1" >
android:id="@+id/radio0"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:checked="true"
android:text="RadioButton" />
android:id="@+id/radio1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="RadioButton" />
If you select a user interface component (an instance of
Open your layout file.
Use the right mouse click on the first radio button to assign the
From now on, I assume you are able to use the properties menu on user interface components. You can always either edit the XML file or modify the properties via right mouse click.
Set the
Assign
Set the
All your user interface components are contained in a layout. Assign a background color to this
Afterwards the background should change to the
Switch to the
View), you can change its properties via the Eclipse Properties View. Most of the properties can be changed via the right mouse menu. You can also edit properties of fields directly in XML. Changing properties in the XML file is much faster, if you know what you want to change. But the right mouse functionality is nice, if you are searching for a certain property. Open your layout file.
Use the right mouse click on the first radio button to assign the
celsius " String attribute to its text property. Assign the fahrenheit string attribute to the text property of the second radio button. From now on, I assume you are able to use the properties menu on user interface components. You can always either edit the XML file or modify the properties via right mouse click.
Set the
Checked property to true for the first RadioButton. Assign
calc to the text property of your button and assign the value onClick to the onClick property. Set the
Input type property to numberSigned and numberDecimal on the EditText. All your user interface components are contained in a layout. Assign a background color to this
Layout. Right-click on an empty space in Graphical Layout mode, then select → → . Select Color and then select myColor in the dialog. Afterwards the background should change to the
whitesmoke color. It might difficult to see the difference. Switch to the
activity_main.xml tab and verify that the XML is correct. xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/myColor" >
android:id="@+id/editText1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:ems="10"
android:inputType="numberSigned|numberDecimal"
>
android:id="@+id/radioGroup1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="@+id/editText1" >
android:id="@+id/radio0"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:checked="true"
android:text="@string/celsius" />
android:id="@+id/radio1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/fahrenheit" />
During the generation of your new Android project you specified that an
Change your
Activity called MainActivity should be created. The project wizard created the corresponding Java class. Change your
MainActivity class to the following isting. Note that the onClick will be called based on the OnClick property of your button. I use the same name as this is easier to remember. package de.vogella.android.temperature; import android.app.Activity; import android.os.Bundle; import android.view.View; import android.widget.EditText; import android.widget.RadioButton; import android.widget.Toast; public class MainActivity extends Activity { private EditText text; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); text = (EditText) findViewById(R.id.editText1); } // This method is called at button click because we assigned the name to the // "OnClick property" of the button public void onClick(View view) { switch (view.getId()) { case R.id.button1: RadioButton celsiusButton = (RadioButton) findViewById(R.id.radio0); RadioButton fahrenheitButton = (RadioButton) findViewById(R.id.radio1); if (text.getText().length() == 0) { Toast.makeText(this, "Please enter a valid number", Toast.LENGTH_LONG).show(); return; } float inputValue = Float.parseFloat(text.getText().toString()); if (celsiusButton.isChecked()) { text.setText(String .valueOf(convertFahrenheitToCelsius(inputValue))); celsiusButton.setChecked(false); fahrenheitButton.setChecked(true); } else { text.setText(String .valueOf(convertCelsiusToFahrenheit(inputValue))); fahrenheitButton.setChecked(false); celsiusButton.setChecked(true); } break; } } // Converts to celsius private float convertFahrenheitToCelsius(float fahrenheit) { return ((fahrenheit - 32) * 5 / 9); } // Converts to fahrenheit private float convertCelsiusToFahrenheit(float celsius) { return ((celsius * 9) / 5) + 32; } }
To start the Android Application, select your project, right click on it, and select → . If an emulator is not yet running, it will be started. Be patient, the emulator starts up very slowly.
Type in a number, select your conversion and press the button. The result should be displayed and the other option should get selected.
Type in a number, select your conversion and press the button. The result should be displayed and the other option should get selected.
After you run your application on the virtual device, you can start it again on the device. If you press the Home button you can select your application.
A layout manager is a subclass of
As of Android 4.0 the most relevant layout managers are
All layouts allow the developer to define attributes. Children can also define attributes which may be evaluated by their parent layout.
Children can specify there desired width and height via the following attributes.
Widgets can uses fixed sizes, e.g. with the
The
ViewGroup and is responsible for the layout of itself and its child Views. Android supports different default layout managers. As of Android 4.0 the most relevant layout managers are
LinearLayout, FrameLayout, RelativeLayout and GridLayout. All layouts allow the developer to define attributes. Children can also define attributes which may be evaluated by their parent layout.
AbsoluteLayoutLayout is deprecated and TableLayout can be implemented more effectively via GridLayout Children can specify there desired width and height via the following attributes.
Table 3. Width and height definition
| android:layout_width | Defines the width of the widget. |
|---|---|
| android:layout_height | Defines the height of the widget. |
Widgets can uses fixed sizes, e.g. with the
dp definition, for example 100dp. While dp is a fixed size it will scale with different device configurations. The
match_parent value tells the to maximize the widget in its parent. The wrap_content value tells the layout to allocate the minimum amount so that widget is rendered correctly. LinearLayout puts all its child elements into a single column or row depending on the android:orientation attribute. Possible values for this attribute are horizontal and vertical, horizontal is the default value. LinearLayout can be nested to achieve more complex layouts. LinearLayout supports assigning a weight to individual children via the android:layout_weight layout parameter. This value specifies how much of the extra space in the layout is allocated to the View. If for example you have two widgets and the first one defines a layout_weight of 1 and the second of 2, the first will get 1/3 of the available space and the other one 2/3. You can also set the layout_width to zero to have always a certain ratio. RelativeLayout allow to position the widget relative to each other. This allows for complex layouts. A simple usage for
RelativeLayout is if you want to center a single component. Just add one component to the RelativeLayout and set the android:layout_centerInParent attribute to true. "1.0"
GridLayout was introduced with Android 4.0. This layout allows you to organize a view into a Grid. GridLayout separates its drawing area into: rows, columns, and cells. You can specify how many columns you want for define for each
View in which row and column it should be placed and how many columns and rows it should use. If not specified GridLayout uses defaults, e.g. one column, one row and the position of a View depends on the order of the declaration of the Views.
The
Of course this
ScrollView class can be used to contain one View that might be to big too fit on one screen. ScrollView will is this case display a scroll bar to scroll the context. Of course this
View can be a layout which can then contain other elements.
Create an android project "de.vogella.android.scrollview" with the activity "ScrollView". Create the following layout and class.
The attribute "android:fillViewport="true"" ensures that the scrollview is set to the full screen even if the elements are smaller then one screen and the "layout_weight" tell the android system that these elements should be extended.
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fillViewport="true"
android:orientation="vertical" >
android:id="@+id/LinearLayout01"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
android:id="@+id/TextView01"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:paddingLeft="8dip"
android:paddingRight="8dip"
android:paddingTop="8dip"
android:text="This is a header"
android:textAppearance="?android:attr/textAppearanceLarge" >
android:id="@+id/TextView02"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_weight="1.0"
android:text="@+id/TextView02" >
android:id="@+id/LinearLayout02"
android:layout_width="wrap_content"
android:layout_height="wrap_content" >
package de.vogella.android.scrollview; import android.app.Activity; import android.os.Bundle; import android.view.View; import android.widget.TextView; public class ScrollView extends Activity {/** Called when the activity is first created. */@Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); TextView view = (TextView) findViewById(R.id.TextView02); String s=""; for (int i=0; i < 100; i++) { s += "vogella.com "; } view.setText(s); } }
The attribute "android:fillViewport="true"" ensures that the scrollview is set to the full screen even if the elements are smaller then one screen and the "layout_weight" tell the android system that these elements should be extended.
Fragments are components which run in the context of an Activity. A Fragment components encapsulate application code so that it is easier to reuse it and to support different sized devices.
Fragments have their own lifecycle and their own user interface. They can be defined via layout files or via coding.
If an Activity stops its Fragments will
also be stopped; if an Activity is destroyed its Fragments will also get destroyed.
If a Fragment component is defined in an XML layout file, the
The base class for Fragments is
The onCreateView() method is called by Android once the
The
Fragments can be dynamically added and removed from an Activity via
Fragments have their own lifecycle and their own user interface. They can be defined via layout files or via coding.
If an Activity stops its Fragments will
also be stopped; if an Activity is destroyed its Fragments will also get destroyed.
If a Fragment component is defined in an XML layout file, the
android:name attribute points to the corresponding class. The base class for Fragments is
android.app.Fragment. For special purposes you can also use more special classes, like ListFragment or DialogFragment. The onCreateView() method is called by Android once the
Fragment should create its user interface. Here you can inflate an layout via the inflate() method call of the Inflator object passed as a parameter to this method. . The
onStart() method is called once the Fragment gets visible. Fragments can be dynamically added and removed from an Activity via
Fragment transactions. This will add the action to the history stack of the Activity, i.e. this will allow to revert the Fragment changes in the Activity via the back button.
Fragments make it easy to re-use components in different layouts, e.g. you can build single-pane layouts for handsets (phones) and multi-pane layouts for tablets.
This is not limited to tablets; for example you can use Fragments also to support different layout for landscape and portrait orientation. But as tablets offer significantly more space you typically include more views into the layout and Fragments makes that easier.
The typical example is a list of items in an activity. On a tablet you see the details immediately on the same screen on the right hand side if you click on item. On a handset you jump to a new detail screen. The following discussion will assume that you have two Fragments (main and detail) but you can also have more. We will also have one main activity and one detailed activity. On a tablet the main activity contains both Fragments in its layout, on a handheld it only contains the main fragment.
To check for an fragment you can use the FragmentManager.
To create different layouts with Fragments you can:
The second approach is the most flexible and in general preferable way of using Fragments. In this case the main activity checks if the detail fragment is available in the layout. If the detailed fragment is there, the main activity tells the fragment that is should update itself. If the detail fragment is not available the main activity starts the detailed activity.
It is good practice that Fragments do not manipulate each other. For this purpose a
This is not limited to tablets; for example you can use Fragments also to support different layout for landscape and portrait orientation. But as tablets offer significantly more space you typically include more views into the layout and Fragments makes that easier.
The typical example is a list of items in an activity. On a tablet you see the details immediately on the same screen on the right hand side if you click on item. On a handset you jump to a new detail screen. The following discussion will assume that you have two Fragments (main and detail) but you can also have more. We will also have one main activity and one detailed activity. On a tablet the main activity contains both Fragments in its layout, on a handheld it only contains the main fragment.
To check for an fragment you can use the FragmentManager.
DetailFragment fragment = (DetailFragment) getFragmentManager(). findFragmentById(R.id.detail_frag); if (fragment==null || ! fragment.isInLayout()) { // start new Activity } else { fragment.update(...); }
To create different layouts with Fragments you can:
- Use one activity, which displays two Fragments for tablets and only one on handsets devices. In this case you would switch the Fragments in the activity whenever necessary. This requires that the fragment is not declared in the layout file as such Fragments cannot be removed during runtime. It also requires an update of the action bar if the action bar status depends on the fragment.
- Use separate activities to host each fragment on a handset. For example, when the tablet UI uses two Fragments in an activity, use the same activity for handsets, but supply an alternative layout that includes just one fragment. When you need to switch Fragments, start another activity that hosts the other fragment.
The second approach is the most flexible and in general preferable way of using Fragments. In this case the main activity checks if the detail fragment is available in the layout. If the detailed fragment is there, the main activity tells the fragment that is should update itself. If the detail fragment is not available the main activity starts the detailed activity.
It is good practice that Fragments do not manipulate each other. For this purpose a
Fragment typically implements an interface to get new data from its host Activity.
The following tutorial demonstrates how to use Fragments. The application will use layouts with different fragments depending on portrait and landscape mode.
In portrait mode the RssfeedActivity will show one Fragment. From this Fragments the user can navigate to another Activity which contains another Fragment.
In landscape mode RssfeedActivity will show both Fragments side by side.
In portrait mode the RssfeedActivity will show one Fragment. From this Fragments the user can navigate to another Activity which contains another Fragment.
In landscape mode RssfeedActivity will show both Fragments side by side.
Create a new Android project with the following data.
Table 4. Android project
| Property | Value |
|---|---|
| Application Name | RSS Reader |
| Project Name | com.example.android.rssfeed |
| Package name | com.example.android.rssfeed |
| Template | BlankActivity |
| Activity | RssfeedActivity |
| Layout | activity_rssfeed |
Create or change the following layout files in the
Create a new layout file called
Create a new layout file called
Change the existing
res/layout/ folder. Create a new layout file called
fragment_rssitem_detail.xml. This layout file will be used by the DetailFragment.
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
android:id="@+id/detailsText"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="center_horizontal|center_vertical"
android:layout_marginTop="20dip"
android:text="Default Text"
android:textAppearance="?android:attr/textAppearanceLarge"
android:textSize="30dip" />
Create a new layout file called
fragment_rsslist_overview.xml. This layout file will be used by the MyListFragment.
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
Change the existing
activity_rssfeed.xml file. This layout will be the default layout for RssfeedActivity and shows two Fragments.
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal" >
android:id="@+id/listFragment"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="match_parent"
android:layout_marginTop="?android:attr/actionBarSize"
class="com.example.android.rssfeed.MyListFragment" >
android:id="@+id/detailFragment"
android:layout_width="0dp"
android:layout_weight="2"
android:layout_height="match_parent"
class="com.example.android.rssfeed.DetailFragment" >
The
RssfeedActivity class remains unmodified. package com.example.android.rssfeed; import android.app.Activity; import android.os.Bundle; public class RssfeedActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_rssfeed); } }
Create now the
Create the
Create the
Fragment classes. Create the
DetailFragment class. package com.example.android.rssfeed; import android.app.Fragment; import android.os.Bundle; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.TextView; public class DetailFragment extends Fragment { @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View view = inflater.inflate(R.layout.fragment_rssitem_detail, container, false); return view; } public void setText(String item) { TextView view = (TextView) getView().findViewById(R.id.detailsText); view.setText(item); } }
Create the
MyListFragment class. Despite its name it will not display a list of items, it will just have a button which allow to send the current time to the details fragment. package com.example.android.rssfeed; import android.app.Fragment; import android.content.Intent; import android.os.Bundle; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.Button; public class MyListFragment extends Fragment { @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View view = inflater.inflate(R.layout.fragment_rsslist_overview, container, false); Button button = (Button) view.findViewById(R.id.button1); button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { updateDetail(); } }); return view; } // May also be triggered from the Activity public void updateDetail() { String newTime = String.valueOf(System.currentTimeMillis()); DetailFragment fragment = (DetailFragment) getFragmentManager() .findFragmentById(R.id.detailFragment); if (fragment != null && fragment.isInLayout()) { fragment.setText(newTime); } } }
The RssfeedActivity should use a special layout files in portrait mode. For this reason create the
In portrait mode Android will check the
Therefore create the following
Also create the
res/layout-port folder. In portrait mode Android will check the
layout-port folder for fitting layout files. If Android does not find a fitting layout file it uses the layout folder. Therefore create the following
activity_rssfeed.xml layout file in the res/layout-port folder.
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
android:id="@+id/listFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="?android:attr/actionBarSize"
class="com.example.android.rssfeed.MyListFragment" />
Also create the
activity_detail.xml layout file. This layout will be used in the DetailActivity. Please note that we could have create this file also in the res/layout folder, but it is only used in portrait mode hence we place it into this folder.
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
android:id="@+id/detailFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
class="com.example.android.rssfeed.DetailFragment" />
Create a new
Ensure that you also register this Activity in the
Activity called DetailActivity with the following class. package com.example.android.rssfeed; import android.app.Activity; import android.content.res.Configuration; import android.os.Bundle; import android.widget.TextView; public class DetailActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // Need to check if Activity has been switched to landscape mode // If yes, finished and go back to the start Activity if (getResources().getConfiguration().orientation == Configuration.ORIENTATION_LANDSCAPE) { finish(); return; } setContentView(R.layout.activity_detail); Bundle extras = getIntent().getExtras(); if (extras != null) { String s = extras.getString("value"); TextView view = (TextView) findViewById(R.id.detailsText); view.setText(s); } } }
Ensure that you also register this Activity in the
AndroidManifest.xml file.
Adjust the List Fragment to display the
Activity in case the other Fragment is not present in the layout. package com.example.android.rssfeed; import android.app.Fragment; import android.content.Intent; import android.os.Bundle; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.Button; public class MyListFragment extends Fragment { @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View view = inflater.inflate(R.layout.fragment_rsslist_overview, container, false); Button button = (Button) view.findViewById(R.id.button1); button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { updateDetail(); } }); return view; } // May also be triggered from the Activity public void updateDetail() { String newTime = String.valueOf(System.currentTimeMillis()); DetailFragment fragment = (DetailFragment) getFragmentManager() .findFragmentById(R.id.detailFragment); if (fragment != null && fragment.isInLayout()) { fragment.setText(newTime); } else { Intent intent = new Intent(getActivity().getApplicationContext(), DetailActivity.class); intent.putExtra("value", newTime); startActivity(intent); } } }
Run your example. If you run the application in portrait mode you should see only one
Fragment. Use Ctrl+F11 to switch the orientation. In horizontal mode you see two Fragments. If you press the button in portrait mode the a new DetailActivity is started and shows the current time. In horizontal mode you see both Fragments.
The ActionBar is located at the top of the Activity that may display the
The following picture show the ActionBar of a typical Google Application with interactive items and a navigation bar.
Activity title, navigation modes, and other interactive items. The following picture show the ActionBar of a typical Google Application with interactive items and a navigation bar.
The application can also open a menu which shows actions via a popup menu. This
The following picture highlights the hardware button and the resulting menu as popup.
One of the reasons why the ActionBar is superior to the
OptionsMenu is only available if the phone has a hardware Options button. Even if the hardware button is available, it is recommended to use the ActionBar, which is available for phones as of Android 4.0. The following picture highlights the hardware button and the resulting menu as popup.
One of the reasons why the ActionBar is superior to the
OptionsMenu, if that it is clearly visible, while the OptionsMenu is only shown on request and the user may not recognize that options are available.
The menu is typically created as an XML resource. To create one select your project, right click on it and select → → → .
Select the Menu option, enter the filename of your choice and press the Finish button.
This will create a new menu file in the
In your Activity you can assign this menu to the ActionBar via the
Select the Menu option, enter the filename of your choice and press the Finish button.
This will create a new menu file in the
res/menu folder of your project. Open this file and select the Layout tab of the Android editor. Via the button you can add new entries. In your Activity you can assign this menu to the ActionBar via the
onCreateOptionsMenu() method. The MenuInflator class allows to inflate menu entries defined in XML to the menu. MenuInflator can get accessed via the getMenuInflator() method in your Activity @Override public boolean onCreateOptionsMenu(Menu menu) { MenuInflater inflater = getMenuInflater(); inflater.inflate(R.menu.mainmenu, menu); return true; }
The
onCreateOptionsMenu() method is only called once. If you want to change the menu later have to call invalidateOptionsMenu() method. Afterwards onCreateOptionsMenu() is called again.
If a menu entry is selected then the
onOptionsItemSelected() method is called. As parameter you receive the menu entry which was selected so that you can react differently to different menu entries. @Override public boolean onOptionsItemSelected(MenuItem item) { switch (item.getItemId()) { case R.id.menuitem1: Toast.makeText(this, "Menu Item 1 selected", Toast.LENGTH_SHORT) .show(); break; case R.id.menuitem2: Toast.makeText(this, "Menu item 2 selected", Toast.LENGTH_SHORT) .show(); break; default: break; } return true; }
The ActionBar also shows an icon of your application. You can also add an action to this icon. If you select this icon the
As of Android 4.1 this code is not required anymore, you can simply set the parentActivityName in the
onOptionsItemSelected() method will be called with the value android.R.id.home. The recommendation is to return to the main Activity in your program. // If home icon is clicked return to main Activity case android.R.id.home: Intent intent = new Intent(this, OverviewActivity.class); intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); startActivity(intent); break;
As of Android 4.1 this code is not required anymore, you can simply set the parentActivityName in the
AndroidManifest.mf file, pointing to the parent Activity.
You can also add a custom
View to the ActionBar. The following code snippet demonstrates that. @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); ActionBar actionBar = getActionBar(); // add the custom view to the action bar actionBar.setCustomView(R.layout.actionbar_view); actionBar.setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM | ActionBar.DISPLAY_SHOW_HOME); }
A contextual action mode activates a temporary ActionBar that overlays the application ActionBar for the duration of a particular sub-task.
The contextual action mode is typically activated by selecting an item or by long clicking on it.
To implemented this, call the
The contextual action mode is typically activated by selecting an item or by long clicking on it.
To implemented this, call the
startActionMode() method on a View or on your Activity. This method gets an ActionMode.Callback object which is responsible for the lifecycle of the contextual ActionBar.
You can also assign a context menu to a
If possible the contextual action mode should be preferred over a context menu.
A context menu for a view is registered via the
View. A context menu is also activated if the user "long presses" the view. If possible the contextual action mode should be preferred over a context menu.
A context menu for a view is registered via the
registerForContextMenu(view) method. The onCreateContextMenu() method is called every time a context menu is activated as the context menu is discarded after its usage. The Android platform may also add options to your View, e.g. EditText provides context options to select text, etc.
This chapter will demonstrate how to create items in the ActionBar and react to the selection of the user.
Create a project called de.vogella.android.socialapp with the
Create a project called de.vogella.android.socialapp with the
Activity called OverviewActivity.
Create a new Menu XML resource called
Press the button and select the Item entry. Maintain a entry similar to the following screenshot. Via the
Add a similar entry to the menu with the ID attribute set to "@+id/menuitem2", and the Title attribute set to "Test". Also set the
The resulting XML will look like the following.
mainmenu.xml. Open the mainmenu.xml file and select the Layout tab of the Android editor. Press the button and select the Item entry. Maintain a entry similar to the following screenshot. Via the
ifRoom attribute you define that the menu entry is displayed in the ActionBar if there is sufficient space available. Add a similar entry to the menu with the ID attribute set to "@+id/menuitem2", and the Title attribute set to "Test". Also set the
ifRoom flag. The resulting XML will look like the following.
"1.0"
>
Change your
OverviewActivity class to the following. package de.vogella.android.socialapp; import android.app.Activity; import android.os.Bundle; import android.view.Menu; import android.view.MenuInflater; import android.view.MenuItem; import android.widget.Toast; public class OverviewActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_overview); } @Override public boolean onCreateOptionsMenu(Menu menu) { MenuInflater inflater = getMenuInflater(); inflater.inflate(R.menu.mainmenu, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { switch (item.getItemId()) { case R.id.menuitem1: Toast.makeText(this, "Menu Item 1 selected", Toast.LENGTH_SHORT) .show(); break; case R.id.menuitem2: Toast.makeText(this, "Menu item 2 selected", Toast.LENGTH_SHORT) .show(); break; default: break; } return true; } }
Run your application. As there is enough space in the ActionBar otherwise you may see the Overflow menu or you have to use the menu button on your phone. If you select one item, you should see a small info message.
Add a
Create a new menu XML resource with the
Change your
If you run this example and long press the
EditText element your main.xml layout file.
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
android:id="@+id/myView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10" >
Create a new menu XML resource with the
contextual.xml file name. Change your
Activity to the following. package de.vogella.android.socialapp; import android.app.Activity; import android.os.Bundle; import android.view.ActionMode; import android.view.Menu; import android.view.MenuInflater; import android.view.MenuItem; import android.widget.Toast; public class OverviewActivity extends Activity { protected Object mActionMode; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); // Define the contextual action mode View view = findViewById(R.id.myView); view.setOnLongClickListener(new View.OnLongClickListener() { // Called when the user long-clicks on someView public boolean onLongClick(View view) { if (mActionMode != null) { return false; } // Start the CAB using the ActionMode.Callback defined above mActionMode = OverviewActivity.this .startActionMode(mActionModeCallback); view.setSelected(true); return true; } }); } @Override public boolean onCreateOptionsMenu(Menu menu) { MenuInflater inflater = getMenuInflater(); inflater.inflate(R.menu.mainmenu, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { Toast.makeText(this, "Just a test", Toast.LENGTH_SHORT).show(); return true; } private ActionMode.Callback mActionModeCallback = new ActionMode.Callback() { // Called when the action mode is created; startActionMode() was called public boolean onCreateActionMode(ActionMode mode, Menu menu) { // Inflate a menu resource providing context menu items MenuInflater inflater = mode.getMenuInflater(); // Assumes that you have "contexual.xml" menu resources inflater.inflate(R.menu.contextual, menu); return true; } // Called each time the action mode is shown. Always called after // onCreateActionMode, but // may be called multiple times if the mode is invalidated. public boolean onPrepareActionMode(ActionMode mode, Menu menu) { return false; // Return false if nothing is done } // Called when the user selects a contextual menu item public boolean onActionItemClicked(ActionMode mode, MenuItem item) { switch (item.getItemId()) { case R.id.toast: Toast.makeText(OverviewActivity.this, "Selected menu", Toast.LENGTH_LONG).show(); mode.finish(); // Action picked, so close the CAB return true; default: return false; } } // Called when the user exits the action mode public void onDestroyActionMode(ActionMode mode) { mActionMode = null; } }; }
If you run this example and long press the
EditText widget, your contextual ActionBar is displayed.
Fragments can also be used in combination with the ActionBar for navigation. For this your main
The ActionBar allows to add tabs to it via the
Fragment> implements TabListener { private Fragment mFragment; private final Activity mActivity; private final String mTag; private final ClassActivity needs to implement a TabListener which is responsible for moving between the tabs. The ActionBar allows to add tabs to it via the
newTab() method. The following code shows such an Activity. It uses two Fragments, called DetailFragment and ImageFragment. At this point you should be able to create these two Fragments yourself. package de.vogella.android.fragment; import android.app.ActionBar; import android.app.ActionBar.Tab; import android.app.ActionBar.TabListener; import android.app.Activity; import android.app.Fragment; import android.app.FragmentTransaction; import android.os.Bundle; public class MainActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); // setup action bar for tabs ActionBar actionBar = getActionBar(); actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); actionBar.setDisplayShowTitleEnabled(false); Tab tab = actionBar .newTab() .setText("First tab") .setTabListener(new MyTabListener(this, "artist", DetailFragment.class)); actionBar.addTab(tab); tab = actionBar .newTab() .setText("Second Tab") .setTabListener(new MyTabListener (this, "album", ImageFragment.class)); actionBar.addTab(tab); } public static class MyTabListener extends
/** * Constructor used each time a new tab is created. * * @param activity * The host Activity, used to instantiate the fragment * @param tag * The identifier tag for the fragment * @param clz * The fragment's Class, used to instantiate the fragment */
public MyTabListener(Activity activity, String tag, Class
Eclipse provides a perspective for interacting with your Android (virtual) device and your Android application program. Select → → → to open this perspective. It includes several
Views which can also be used independently and allows for example the application to place calls and send SMS to the device. It also allows the application to set the current geo position and allows you to perform a performance trace of your application.
You can see the log (including System.out.print() statements) via the LogCat view.
In general there are you restrictions how to deploy an Android application to your device. You can use USB, email yourself the application or use one of the many Android markets to install the application. The following describes the most common ones.
Turn on USB Debugging on your device in the settings. Select in the settings of your device → , then enable USB debugging.
You may also need to install the a driver for your mobile phone. Linux and Mac OS usually work out of the box while an Windows OS typically requires the installation of a driver.
For details please see Developing on a Device . Please note that the Android version you are developing for must be the installed version on your phone.
If you have only one device connected and no emulator running, the Android develoment tools will automatically deploy to this device. If you have several connected you can selected which one shoudl be used.
You may also need to install the a driver for your mobile phone. Linux and Mac OS usually work out of the box while an Windows OS typically requires the installation of a driver.
For details please see Developing on a Device . Please note that the Android version you are developing for must be the installed version on your phone.
If you have only one device connected and no emulator running, the Android develoment tools will automatically deploy to this device. If you have several connected you can selected which one shoudl be used.
Android application must be signed before they can get installed on an Android device. During development Eclipse signs your application automatically with a debug key.
If you want to install your application without the Eclipse IDE you can right click on it and select → .
This wizard allows to use an existing key or to create a new one.
Please note that you need to use the same signature key in Google Play (Google Market) to update your application. If you loose the key you will NOT be able to update your application ever again.
Make sure to backup your key.
If you want to install your application without the Eclipse IDE you can right click on it and select → .
This wizard allows to use an existing key or to create a new one.
Please note that you need to use the same signature key in Google Play (Google Market) to update your application. If you loose the key you will NOT be able to update your application ever again.
Make sure to backup your key.
Android allow to install applications also directly. Just click on a link which points to an .apk file, e.g. in an email attachment or on a webpage. Android will prompt you if you want to install this application.
This requires a setting on the Android device which allows the installation of non-market application. Typically this setting can be found under the "Security" settings.
This requires a setting on the Android device which allows the installation of non-market application. Typically this setting can be found under the "Security" settings.
Google Play requires a one time fee, currently 25 Dollar. After that the developer can directly upload his application and the required icons, under Google Play Publishing .
Google performs some automatic scanning of applications, but no approval process is in place. All application, which do not contain malware, will be published. Usually a few minutes after upload, the application is available.
Google performs some automatic scanning of applications, but no approval process is in place. All application, which do not contain malware, will be published. Usually a few minutes after upload, the application is available.
Before posting questions, please see the vogella FAQ. If you have questions or find an error in this article please use the www.vogella.com Google Group. I have created a short list how to create good questions which might also help you.
Android ListView and ListActivity
Android SQlite Database
Android Widgets
Android Live Wallpaper
Android Services
Android Location API and Google Maps
Android Intents
Android and Networking
Android Homepage
Android Developer Homepage
Android Issues / Bugs
Android Google Groups
Android Live Folder
Android SQlite Database
Android Widgets
Android Live Wallpaper
Android Services
Android Location API and Google Maps
Android Intents
Android and Networking
Android Homepage
Android Developer Homepage
Android Issues / Bugs
Android Google Groups
Android Live Folder
vogella Training Android and Eclipse Training from the vogella team
Android Tutorial Introduction to Android Programming
GWT Tutorial Program in Java and compile to JavaScript and HTML
Eclipse RCP Tutorial Create native applications in Java
JUnit Tutorial Test your application
Git Tutorial Put everything you have under distributed version control system
Android Tutorial Introduction to Android Programming
GWT Tutorial Program in Java and compile to JavaScript and HTML
Eclipse RCP Tutorial Create native applications in Java
JUnit Tutorial Test your application
Git Tutorial Put everything you have under distributed version control system
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