Developing In Eclipse, with ADT

The Android Development Tools (ADT) plugin for Eclipse adds powerful extensions to the Eclipse integrated development environment. It allows you to create and debug Android applications easier and faster. If you use Eclipse, the ADT plugin gives you an incredible boost in developing Android applications:

  • It gives you access to other Android development tools from inside the Eclipse IDE. For example, ADT lets you access the many capabilities of the DDMS tool: take screenshots, manage port-forwarding, set breakpoints, and view thread and process information directly from Eclipse.
  • It provides a New Project Wizard, which helps you quickly create and set up all of the basic files you'll need for a new Android application.
  • It automates and simplifies the process of building your Android application.
  • It provides an Android code editor that helps you write valid XML for your Android manifest and resource files.
  • It will even export your project into a signed APK, which can be distributed to users.

To begin developing Android applications in the Eclipse IDE with ADT, you first need to download the Eclipse IDE and then download and install the ADT plugin. To do so, follow the steps given in Installing the ADT Plugin.

If you are already developing applications using a version of ADT earlier than 0.9, make sure to upgrade to the latest version before continuing. See the guide to Updating Your ADT Plugin.

Note: This guide assumes you are using the latest version of the ADT plugin. While most of the information covered also applies to previous versions, if you are using an older version, you may want to consult this document from the set of documentation included in your SDK package (instead of the online version).

Creating an Android Project

The ADT plugin provides a New Project Wizard that you can use to quickly create a new Android project (or a project from existing code). To create a new project:

  1. Select File > New > Project.
  2. Select Android > Android Project, and click Next.
  3. Select the contents for the project:
    • Enter a Project Name. This will be the name of the folder where your project is created.
    • Under Contents, select Create new project in workspace. Select your project workspace location.
    • Under Target, select an Android target to be used as the project's Build Target. The Build Target specifies which Android platform you'd like your application built against.

      Unless you know that you'll be using new APIs introduced in the latest SDK, you should select a target with the lowest platform version possible.

      Note: You can change your the Build Target for your project at any time: Right-click the project in the Package Explorer, select Properties, select Android and then check the desired Project Target.

    • Under Properties, fill in all necessary fields.
      • Enter an Application name. This is the human-readable title for your application — the name that will appear on the Android device.
      • Enter a Package name. This is the package namespace (following the same rules as for packages in the Java programming language) where all your source code will reside.
      • Select Create Activity (optional, of course, but common) and enter a name for your main Activity class.
      • Enter a Min SDK Version. This is an integer that indicates the minimum API Level required to properly run your application. Entering this here automatically sets the minSdkVersion attribute in the <uses-sdk> of your Android Manifest file. If you're unsure of the appropriate API Level to use, copy the API Level listed for the Build Target you selected in the Target tab.
  4. Click Finish.

Tip: You can also start the New Project Wizard from the New icon in the toolbar.

Once you complete the New Project Wizard, ADT creates the following folders and files in your new project:

Includes your stub Activity Java file. All other Java files for your application go here.
<Android Version>/ (e.g., Android 1.1/)
Includes the android.jar file that your application will build against. This is determined by the build target that you have chosen in the New Project Wizard.
This contains the Java files generated by ADT, such as your file and interfaces created from AIDL files.
This is empty. You can use it to store raw asset files.
A folder for your application resources, such as drawable files, layout files, string values, etc. See Application Resources.
The Android Manifest for your project. See The AndroidManifest.xml File.
This file contains project settings, such as the build target. This files is integral to the project, as such, it should be maintained in a Source Revision Control system. It should never be edited manually — to edit project properties, right-click the project folder and select "Properties".

Creating an AVD

An Android Virtual Device (AVD) is a device configuration for the emulator that allows you to model real world devices. In order to run an instance of the emulator, you must create an AVD.

To create an AVD from Eclipse:

  1. Select Window > Android SDK and AVD Manager, or click the Android SDK and AVD Manager icon in the Eclipse toolbar.

  2. In the Virtual Devices panel, you'll see a list of existing AVDs. Click New to create a new AVD.
  3. Fill in the details for the AVD.

    Give it a name, a platform target, an SD card size, and a skin (HVGA is default).

    Note: Be sure to define a target for your AVD that satisfies your application's Build Target (the AVD platform target must have an API Level equal to or greater than the API Level that your application compiles against).

  4. Click Create AVD.

Your AVD is now ready and you can either close the SDK and AVD Manager, create more AVDs, or launch an emulator with the AVD by selecting a device and clicking Start.

For more information about AVDs, read the Android Virtual Devices documentation.

Running Your Application

Running your application from Eclipse will usually require just a couple clicks, whether you're running it on the emulator or on an attached device. The information below describes how to get set up and run your application from Eclipse.

Running on the emulator

Before you can run your application on the Android Emulator, you must create an AVD.

To run (or debug) your application, select Run > Run (or Run > Debug) from the Eclipse menu bar. The ADT plugin will automatically create a default launch configuration for the project. Eclipse will then perform the following:

  1. Compile the project (if there have been changes since the last build).
  2. Create a default launch configuration (if one does not already exist for the project).
  3. Install and start the application on an emulator (or device), based on the Deployment Target defined by the run configuration.

    By default, Android run configurations use an "automatic target" mode for selecting a device target. For information on how automatic target mode selects a deployment target, see Automatic and manual target modes below.

If debugging, the application will start in the "Waiting For Debugger" mode. Once the debugger is attached, Eclipse will open the Debug perspective.

To set or change the launch configuration used for your project, use the launch configuration manager. See Creating a Run Configuration for information.

Be certain to create multiple AVDs upon which to test your application. You should have one AVD for each platform and screen type with which your application is compatible. For instance, if your application compiles against the Android 1.5 (API Level 3) platform, you should create an AVD for each platform equal to and greater than 1.5 and an AVD for each screen type you support, then test your application on each one.

Running on a device

Before you can run your application on a device, you must perform some basic setup for your device:

  • Declare your application as debuggable in your manifest
  • Enable USB Debugging on your device
  • Ensure that your development computer can detect your device when connected via USB

Read Setting up a Device for Development for more information.

Once set up and your device is connected via USB, install your application on the device by selecting Run > Run (or Run > Debug) from the Eclipse menu bar.

Creating a Run Configuration

The run configuration specifies the project to run, the Activity to start, the emulator or connected device to use, and so on. When you first run a project as an Android Application, ADT will automatically create a run configuration. The default run configuration will launch the default project Activity and use automatic target mode for device selection (with no preferred AVD). If the default settings don't suit your project, you can customize the launch configuration or even create a new.

To create or modify a launch configuration, follow these steps as appropriate for your Eclipse version:

  1. Open the run configuration manager.
    • In Eclipse 3.3 (Europa), select Run > Open Run Dialog (or Open Debug Dialog)
    • In Eclipse 3.4 (Ganymede), select Run > Run Configurations (or Debug Configurations)
  2. Expand the Android Application item and create a new configuration or open an existing one.
    • To create a new configuration:
      1. Select Android Application and click the New launch configuration icon above the list (or, right-click Android Application and click New).
      2. Enter a Name for your configuration.
      3. In the Android tab, browse and select the project you'd like to run with the configuration.
    • To open an existing configuration, select the configuration name from the list nested below Android Application.
  3. Adjust your desired launch configuration settings.

    In the Target tab, consider whether you'd like to use Manual or Automatic mode when selecting an AVD to run your application. See the following section on Automatic and manual target modes).

    You can specify any emulator options to the Additional Emulator Command Line Options field. For example, you could add -scale 96dpi to scale the AVD's screen to an accurate size, based on the dpi of your computer monitor. For a full list of emulator options, see the Android Emulator document.

Automatic and manual target modes

By default, a run configuration uses the automatic target mode in order to select an AVD. In this mode, ADT will select an AVD for the application in the following manner:

  1. If there's a device or emulator already running and its AVD configuration meets the requirements of the application's build target, the application is installed and run upon it.
  2. If there's more than one device or emulator running, each of which meets the requirements of the build target, a "device chooser" is shown to let you select which device to use.
  3. If there are no devices or emulators running that meet the requirements of the build target, ADT looks at the available AVDs. If one meets the requirements of the build target, the AVD is used to launch a new emulator, upon which the application is installed and run.
  4. If all else fails, the application will not be run and you will see a console error warning you that there is no existing AVD that meets the build target requirements.

However, if a "preferred AVD" is selected in the run configuration, then the application will always be deployed to that AVD. If it's not already running, then a new emulator will be launched.

If your run configuration uses manual mode, then the "device chooser" is presented every time that your application is run, so that you can select which AVD to use.

Signing your Applications

As you begin developing Android applications, understand that all Android applications must be digitally signed before the system will install them on an emulator or an actual device. There are two ways to do this: with a debug key (for immediate testing on an emulator or development device) or with a private key (for application distribution).

The ADT plugin helps you get started quickly by signing your .apk files with a debug key, prior to installing them on an emulator or development device. This means that you can quickly run your application from Eclipse without having to generate your own private key. No specific action on your part is needed, provided ADT has access to Keytool.However, please note that if you intend to publish your application, you must sign the application with your own private key, rather than the debug key generated by the SDK tools.

Please read Signing Your Applications, which provides a thorough guide to application signing on Android and what it means to you as an Android application developer. The document also includes a guide to exporting and signing your application with the ADT's Export Wizard.

Working with Library Projects

An Android library project is a development project that holds shared Android source code and resources. Other Android application projects can reference the library project and, at build time, include its compiled sources in their .apk files. Multiple application projects can reference the same library project and any single application project can reference multiple library projects.

If you have source code and resources that are common to multiple application projects, you can move them to a library project so that it is easier to maintain across applications and versions. Here are some common scenarios in which you could make use of library projects:

  • If you are developing multiple related applications that use some of the same components, you could move the redundant components out of their respective application projects and create a single, reuseable set of the same components in a library project.
  • If you are creating an application that exists in both free and paid versions, you could move the part of the application that is common to both versions into a library project. The two dependent projects, with their different package names, will reference the library project and provide only the difference between the two application versions.

Structurally, a library project is similar to a standard Android application project. For example, it includes a manifest file at the project root, as well as src/, res/ and similar directories. The project can contain the same types of source code and resources as a standard Android project, stored in the same way. For example, source code in the library project can access its own resources through its R class.

However, a library project differs from an standard Android application project in that you cannot compile it directly to its own .apk or run it on the Android platform. Similarly, you cannot export the library project to a self-contained JAR file, as you would do for a true library. Instead, you must compile the library indirectly, by referencing the library from a dependent application's build path, then building that application.

When you build an application that depends on a library project, the SDK tools compile the library and merge its sources with those in the main project, then use the result to generate the .apk. In cases where a resource ID is defined in both the application and the library, the tools ensure that the resource declared in the application gets priority and that the resource in the library project is not compiled into the application .apk. This gives your application the flexibility to either use or redefine any resource behaviors or values that are defined in any library.

To organize your code further, your application can add references to multiple library projects, then specify the relative priority of the resources in each library. This lets you build up the resources actually used in your application in a cumulative manner. When two libraries referenced from an application define the same resource ID, the tools select the resource from the library with higher priority and discard the other.

ADT lets you add references to library projects and set their relative priority from the application project's Properties. As shown in Figure 2, below, once you've added a reference to a library project, you can use the Up and Down controls to change the ordering, with the library listed at the top getting the higher priority. At build time, the libraries are merged with the application one at a time, starting from the lowest priority to the highest.

Note that a library project cannot itself reference another library project and that, at build time, library projects are not merged with each other before being merged with the application. However, note that a library can import an external library (JAR) in the normal way.

The sections below describe how to use ADT to set up and manage library your projects. Once you've set up your library projects and moved code into them, you can import library classes and resources to your application in the normal way.

Development requirements

Android library projects are a build-time construct, so you can use them to build a final application .apk that targets any API level and is compiled against any version of the Android library.

However, to use library projects, you need to update your development environment to use the latest tools and platforms, since older releases of the tools and platforms do not support building with library projects. Specifically, you need to download and install the versions listed below:

Table 1. Minimum versions of SDK tools and plaforms on which you can develop library projects.

Component Minimum Version
SDK Tools r6 (or higher)
Android 2.2 platformr1 (or higher)
Android 2.1 platformr2 (or higher)
Android 2.0.1 platformnot supported
Android 2.0 platformnot supported
Android 1.6 platformr3 (or higher)
Android 1.5 platformr4 (or higher)
ADT Plugin0.9.7 (or higher)

You can download the tools and platforms using the Android SDK and AVD Manager, as described in Adding SDK Components. To install or update ADT, use the Eclipse Updater as described in ADT Plugin for Eclipse.

Setting up a library project

A library project is a standard Android project, so you can create a new one in the same way as you would a new application project. Specifically, you can use the New Project Wizard, as described in Creating an Android Project, above.

When you are creating the library project, you can select any application name, package, and set other fields as needed, as shown in the diagram below. Click Finish to create the project in the workspace.

Next, set the project's Properties to indicate that it is a library project:

  1. In the Package Explorer, right-click the library project and select Properties.
  2. In the Properties window, select the "Android" properties group at left and locate the Library properties at right.
  3. Select the "is Library" checkbox and click Apply.
  4. Click OK to close the Properties window.

The new project is now marked as a library project. You can begin moving source code and resources into it, as described in the sections below.

You can also convert an existing application project into a library. To do so, simply open the Properties for the project and select the "is Library" checkbox. Other application projects can now reference the existing project as a library project.

Figure 1. Marking a project as an Android library project.

Creating the manifest file

A library project's manifest file must declare all of the shared components that it includes, just as would a standard Android application. For more information, see the documentation for AndroidManifest.xml.

For example, the TicTacToeLib example library project declares the Activity GameActivity:

    <activity android:name="GameActivity" />

Referencing a library project from an application

If you are developing an application and want to include the shared code or resources from a library project, you can do so easily by adding a reference to the library project in the application project's Properties.

To add a reference to a library project, follow these steps:

  1. In the Package Explorer, right-click the dependent project and select Properties.
  2. In the Properties window, select the "Android" properties group at left and locate the Library properties at right.
  3. Click Add to open the Project Selection dialog.
  4. From the list of available library projects, select a project and click OK.
  5. When the dialog closes, click Apply in the Properties window.
  6. Click OK to close the Properties window.

As soon as the Properties dialog closes, Eclipse rebuilds the project, including the contents of the library project.

The figure below shows the Properties dialog that lets you add library references and move them up and down in priority.

Figure 2. Adding a reference to a library project in the properties of an application project.

If you are adding references to multiple libraries, note that you can set their relative priority (and merge order) by selecting a library and using the Up and Down controls. The tools merge the referenced libraries with your application starting from lowest priority (bottom of the list) to highest (top of the list). If more than one library defines the same resource ID, the tools select the resource from the library with higher priority. The application itself has highest priority and its resources are always used in preference to identical resource IDs defined in libraries.

Declaring library components in the the manifest file

In the manifest file of the application project, you must add declarations of all components that the application will use that are imported from a library project. For example, you must declare any <activity>, <service>, <receiver>, <provider>, and so on, as well as <permission>, <uses-library>, and similar elements.

Declarations should reference the library components by their fully-qualified package names, where appropriate.

For example, the TicTacToeMain example application declares the library Activity GameActivity like this:

    <activity android:name="" />

For more information about the manifest file, see the documentation for AndroidManifest.xml.

Development considerations

As you develop your library project and dependent applications, keep the points listed below in mind.

Resource conflicts

Since the tools merge the resources of a library project with those of a dependent application project, a given resource ID might be defined in both projects. In this case, the tools select the resource from the application, or the library with highest priority, and discard the other resource. As you develop your applications, be aware that common resource IDs are likely to be defined in more than one project and will be merged, with the resource from the application or highest-priority library taking precedence.

Using prefixes to avoid resource conflicts

To avoid resource conflicts for common resource IDs, consider using a prefix or other consistent naming scheme that is unique to the project (or is unique across all projects).

No export of library project to JAR

A library cannot be distributed as a binary file (such as a jar file). This is because the library project is compiled by the main project to use the correct resource IDs.

A library project can include a JAR library

You can develop a library project that itself includes a JAR library, however you need to manually edit the dependent application project's build path and add a path to the JAR file.

A library project can depend on an external JAR library

You can develop a library project that depends on an external library (for example, the Maps external library). In this case, the dependent application must build against a target that includes the external library (for example, the Google APIs Add-On). Note also that both the library project and the dependent application must declare the external library their manifest files, in a <uses-library> element.

Library project can not include raw assets

The tools do not support the use of raw asset files in a library project. Any asset resources used by an application must be stored in the assets/ directory of the application project itself.

Targeting different Android platform versions in library project and application project

A library is compiled as part of the dependent application project, so the API used in the library project must be compatible with the version of the Android library used to compile the application project. In general, the library project should use an API level that is the same as — or lower than — that used by the application. If the library project uses an API level that is higher than that of the application, the application project will fail to compile. It is perfectly acceptable to have a library that uses the Android 1.5 API (API level 3) and that is used in an Android 1.6 (API level 4) or Android 2.1 (API level 7) project, for instance.

No restriction on library package name

There is no requirement for the package name of a library to be the same as that of applications that use it.

Multiple R classes in gen/ folder of application project

When you build the dependent application project, the code of any libraries is compiled and merged to the application project. Each library has its own R class, named according to the library's package name. The R class generated from the resources of the main project and of the library is created in all the packages that are needed including the main project’s package and the libraries’ packages.

Testing a library project

There are two recommended ways of setting up testing on code and resources in a library project:

  • You can set up a test project that instruments an application project that depends on the library project. You can then add tests to the project for library-specific features.
  • You can set up a set up a standard application project that depends on the library and put the instrumentation in that project. This lets you create a self-contained project that contains both the tests/instrumentations and the code to test.

Library project storage location

There are no specific requirements on where you should store a library project, relative to a dependent application project, as long as the application project can reference the library project by a relative link. You can place the library project What is important is that the main project can reference the library project through a relative link.

Migrating library projects to ADT 0.9.8

This section provides information about how to migrate a library project created with ADT 0.9.7 to ADT 0.9.8 (or higher). The migration is needed only if you are developing in Eclipse with ADT and assumes that you have also upgraded to SDK Tools r7 (or higher).

The way that ADT handles library projects has changed between ADT 0.9.7 and ADT 0.9.8. Specifically, in ADT 0.9.7, the src/ source folder of the library was linked into the dependent application project as a folder that had the same name as the library project. This worked because of two restrictions on the library projects:

  • The library was only able to contain a single source folder (excluding the special gen/ source folder), and
  • The source folder was required to have the name src/ and be stored at the root of the project.

In ADT 0.9.8, both of those restrictions were removed. A library project can have as many source folders as needed and each can have any name. Additionally, a library project can store source folders in any location of the project. For example, you could store sources in a src/java/ directory. In order to support this, the name of the linked source folders in the main project are now called <library-name>_<folder-name> For example: MyLibrary_src/ or MyLibrary_src_java/.

Additionally, the linking process now flags those folders in order for ADT to recognize that it created them. This will allow ADT to automatically migrate the project to new versions of ADT, should they contain changes to the handling of library projects. ADT 0.9.7 did not flag the linked source folders, so ADT 0.9.8 cannot be sure whether the old linked folders can be removed safely. After upgrading ADT to 0.9.8, you will need to remove the old linked folders manually in a simple two-step process, as described below.

Before you begin, make sure to create a backup copy of your application or save the latest version to your code version control system. This ensures that you will be able to easily revert the migration changes in case there is a problem in your environment.

When you first upgrade to ADT 0.9.8, your main project will look as shown below, with two linked folders (in this example, MyLibrary and MyLibrary_src — both of which link to MyLibrary/src. Eclipse shows an error on one of them because they are duplicate links to a single class.

To fix the error, remove the linked folder that does not contain the _src suffix.

  1. Right click the folder that you want to remove (in this case, the MyLibrary folder) and choose Build Path > Remove from Build Path, as shown below.
  2. Next, When asked about unlinking the folder from the project, select Yes, as shown below.

This should resolve the error and migrate your library project to the new ADT environment.

Eclipse Tips

Executing arbitrary Java expressions in Eclipse

You can execute arbitrary code when paused at a breakpoint in Eclipse. For example, when in a function with a String argument called "zip", you can get information about packages and call class methods. You can also invoke arbitrary static methods: for example, entering android.os.Debug.startMethodTracing() will start dmTrace.

Open a code execution window, select Window > Show View > Display from the main menu to open the Display window, a simple text editor. Type your expression, highlight the text, and click the 'J' icon (or CTRL + SHIFT + D) to run your code. The code runs in the context of the selected thread, which must be stopped at a breakpoint or single-step point. (If you suspend the thread manually, you have to single-step once; this doesn't work if the thread is in Object.wait().)

If you are currently paused on a breakpoint, you can simply highlight and execute a piece of source code by pressing CTRL + SHIFT + D.

You can highlight a block of text within the same scope by pressing ALT +SHIFT + UP ARROW to select larger and larger enclosing blocks, or DOWN ARROW to select smaller blocks.

Here are a few sample inputs and responses in Eclipse using the Display window.

Input Response
zip (java.lang.String) /work/device/out/linux-x86-debug/android/app/
zip.endsWith(".zip") (boolean) true
zip.endsWith(".jar") (boolean) false

You can also execute arbitrary code when not debugging by using a scrapbook page. Search the Eclipse documentation for "scrapbook".

Running DDMS Manually

Although the recommended way to debug is to use the ADT plugin, you can manually run DDMS and configure Eclipse to debug on port 8700. (Note: Be sure that you have first started DDMS).

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