Doc change: adding Projects section of dev guide

page.title=Creating and Managing Projects

@jd:body

 <div id="qv-wrapper">

    <div id="qv">

      <h2>In this document</h2>

      <ol>

        <li><a href="#ApplicationProjects">Android Projects</a></li>

        <li><a href="#LibraryProjects">Library Projects</a></li>

        <li><a href="#TestProjects">Test Projects</a></li>

      </ol>

    </div>

  </div>

  <p>Projects act as containers for storing things such as code and resource files. The SDK tools

  expect your projects to follow a specific structure so it can compile and package your

  application correctly, so it is highly recommended that you create them with Eclipse and ADT or

  with the <code>android</code> tool on the command line. There are three types of projects, and

  they all share the same general structure but differ in function:</p>

  <dl>

    <dt><strong>Android Projects</strong></dt>

    <dd>An Android project is the container for your application's source code, resource files, and

    files such as the Ant build and Android Manifest file. An application project is the main type

    of project and the contents are eventually built into an <code>.apk</code> file that you install on a

    device.</dd>

    <dt><strong>Test Projects</strong></dt>

    <dd>These projects contain code to test your application projects and are built into

    applications that run on a device.</dd>

    <dt><strong>Library Projects</strong></dt>

    <dd>These projects contain shareable Android source code and resources that you can reference

    in Android projects. This is useful when you have common code that you want to reuse. 

    Library projects cannot be installed onto a device, however, they are

    pulled into the <code>.apk</code> file at build time.</dd>

  </dl>

  <p>When you use the Android development tools to create a new project, the essential files and

  folders will be created for you. There are only a handful of files and folders generated for you,

  and some of them depend on whether you use the Eclipse plugin or the {@code android} tool to

  generate your project. As your application grows in complexity, you might require new kinds of

  resources, directories, and files.</p>

  <h2 id="ApplicationProjects">Android Projects</h2>

  <p>Android projects are the projects that eventually get built into an <code>.apk</code> file that you install

  onto a device. They contain things such as application source code and resource files.

  Some are generated for you by default, while others should be created if

  required. The following directories and files comprise an Android project:</p>

  <dl>

    <dt><code>src/</code></dt>

    <dd>Contains your stub Activity file, which is stored at

    <code>src<em>/your/package/namespace/ActivityName</em>.java</code>. All other source code

     files (such as <code>.java</code> or <code>.aidl</code> files) go here as well.</dd>

    <dt><code>bin</code></dt>

    <dd>Output directory of the build. This is where you can find the final <code>.apk</code> file and other

    compiled resources.</dd>

    <dt><code>jni</code></dt>

    <dd>Contains native code sources developed using the Android NDK. For more information, see the

    <a href="{@docRoot}sdk/ndk/index.html">Android NDK documentation</a>.</dd>

    <dt><code>gen/</code></dt>

    <dd>Contains the Java files generated by ADT, such as your <code>R.java</code> file and

    interfaces created from AIDL files.</dd>

    <dt><code>assets/</code></dt>

    <dd>This is empty. You can use it to store raw asset files. Files that you save here are

    compiled into an <code>.apk</code> file as-is, and the original filename is preserved. You can navigate this

    directory in the same way as a typical file system using URIs and read files as a stream of

    bytes using the the {@link android.content.res.AssetManager}. For example, this is a good

    location for textures and game data.</dd>

    <dt><code>res/</code></dt>

    <dd>

      Contains application resources, such as drawable files, layout files, and string values. See

      <a href="{@docRoot}guide/topics/resources/index.html">Application Resources</a> for more

      information.

      <dl>

        <dt><code>anim/</code></dt>

        <dd>For XML files that are compiled into animation objects. See the <a href=

        "{@docRoot}guide/topics/resources/animation-resource.html">Animation</a> resource

        type.</dd>

        <dt><code>color/</code></dt>

        <dd>For XML files that describe colors. See the <a href=

        "{@docRoot}guide/topics/resources/color-list-resource.html">Color Values</a> resource

        type.</dd>

        <dt><code>drawable/</code></dt>

        <dd>For bitmap files (PNG, JPEG, or GIF), 9-Patch image files, and XML files that describe

        Drawable shapes or a Drawable objects that contain multiple states (normal, pressed, or

        focused). See the <a href=

        "{@docRoot}guide/topics/resources/drawable-resource.html">Drawable</a> resource type.</dd>

        <dt><code>layout/</code></dt>

        <dd>XML files that are compiled into screen layouts (or part of a screen). See the <a href=

        "{@docRoot}guide/topics/resources/layout-resource.html">Layout</a> resource type.</dd>

        <dt><code>menu/</code></dt>

        <dd>For XML files that define application menus. 

        See the <a href="{@docRoot}guide/topics/resources/menu-resource.html">Menus</a>

        resource type.</dd>

        <dt><code>raw/</code></dt>

        <dd>For arbitrary raw asset files. Saving asset files here instead of in the

        <code>assets/</code> directory only differs in the way that you access them. These files

        are processed by aapt and must be referenced from the application using a resource

        identifier in the {@code R} class. For example, this is a good place for media, such as MP3

        or Ogg files.</dd>

        <dt><code>values/</code></dt>

        <dd>For XML files that are compiled into many kinds of resource. Unlike other resources in

        the <code>res/</code> directory, resources written to XML files in this folder are not

        referenced by the file name. Instead, the XML element type controls how the resources is

        defined within them are placed into the {@code R} class.</dd>

        <dt><code>xml/</code></dt>

        <dd>For miscellaneous XML files that configure application components. For example, an XML

        file that defines a {@link android.preference.PreferenceScreen}, {@link

        android.appwidget.AppWidgetProviderInfo}, or <a href=

        "{@docRoot}reference/android/app/SearchManager.html#SearchabilityMetadata">Searchability

        Metadata</a>. See <a href="{@docRoot}guide/topics/resources/index.html">Application Resources</a>

        for more information about configuring these application components.</dd>

      </dl>

    </dd>

    <dt><code>libs/</code></dt>

    <dd>Contains private libraries.</dd>

    <dt><code>AndroidManifest.xml</code></dt>

    <dd>The control file that describes the nature of the application and each of its components.

    For instance, it describes: certain qualities about the activities, services, intent receivers,

    and content providers; what permissions are requested; what external libraries are needed; what

    device features are required, what API Levels are supported or required; and others. See the

    <a href="{@docRoot}guide/topics/manifest/manifest-intro.html">AndroidManifest.xml</a>

    documentation for more information</dd>

    <dt><code>build.properties</code></dt>

    <dd>Customizable properties for the build system. You can edit this file to override default

    build settings used by Ant and provide a pointer to your keystore and key alias so that the

    build tools can sign your application when built in release mode. If you use Eclipse, this file

    is not used.</dd>

    <dt><code>build.xml</code></dt>

    <dd>The Ant build file for your project. This is only applicable for projects that

    you create on the command line.</dd>

    <dt><code>default.properties</code></dt>

    <dd>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. Do not edit

    the file manually.</dd>

  </dl>

  <h2 id="LibraryProjects">Library Projects</h2>

  <div class="sidebox-wrapper">

    <div class="sidebox">

      <h2>Library project example code</h2>

      <p>The SDK includes an example application called <code>TicTacToeMain</code> that shows how a dependent

      application can use code and resources from an Android Library project. The TicTacToeMain

      application uses code and resources from an example library project called TicTacToeLib.</p>

      <p>To download the sample applications and run them as projects in

      your environment, use the <em>Android SDK and AVD Manager</em> to download the "Samples for

      SDK API 8" component into your SDK.</p>

      <p>For more information and to browse the code of the samples, see

      the <a href="{@docRoot}resources/samples/TicTacToeMain/index.html">TicTacToeMain

      application</a>.</p>

    </div>

  </div>

    <p>An Android <em>library project</em> 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 <code>.apk</code> files. Multiple

    application projects can reference the same library project and any single application project

    can reference multiple library projects.</p>

    <p>If you have source code and resources that are common to multiple Android 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:</p>

    <ul>

      <li>If you are developing multiple related applications that use some of the same components,

      you move the redundant components out of their respective application projects and create a

      single, reuseable set of the same components in a library project.</li>

      <li>If you are creating an application that exists in both free and paid versions. You 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.</li>

    </ul>

    <p>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 <code>src/</code>,

    <code>res/</code> 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 <code>R</code> class.</p>

    <p>However, a library project differs from an standard Android application project in that you

    cannot compile it directly to its own <code>.apk</code> and run it on an Android device.

    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 in the dependent application and building that application.</p>

    <p>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 <code>.apk</code>. 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 <code>.apk</code>.

    This gives your application the flexibility to either use or redefine any resource behaviors or

    values that are defined in any library.</p>

    <p>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.</p>

    <p>Once you have added references to library projects to your Android project, 

    you can set their relative priority. At build time, the

    libraries are merged with the application one at a time, starting from the lowest priority to

    the highest.</p>

    <p>Note that a library project cannot itself reference another library project and that, at

    build time, library projects are <em>not</em> 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.</p>

  <h3 id="libraryReqts">Development requirements</h3>

  <p>Android library projects are a build-time construct, so you can use them to build a final

  application <code>.apk</code> that targets any API level and is compiled against any version of

  the Android library.</p>

  <p>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:</p>

  <p class="table-caption"><strong>Table 1.</strong> Minimum versions of SDK tools and platforms on

  which you can develop library projects.</p>

  <table>

    <tr>

      <th>Component</th>

      <th>Minimum Version</th>

    </tr>

    <tr>

      <td>SDK Tools</td>

      <td>r6 (or higher)</td>

    </tr>

    <tr>

      <td>Android 2.2 platform</td>

      <td>r1 (or higher)</td>

    </tr>

    <tr>

      <td>Android 2.1 platform</td>

      <td>r2 (or higher)</td>

    </tr>

    <tr>

      <td style="color:gray">Android 2.0.1 platform</td>

      <td style="color:gray"><em>not supported</em></td>

    </tr>

    <tr>

      <td style="color:gray">Android 2.0 platform</td>

      <td style="color:gray"><em>not supported</em></td>

    </tr>

    <tr>

      <td>Android 1.6 platform</td>

      <td>r3 (or higher)</td>

    </tr>

    <tr>

      <td>Android 1.5 platform</td>

      <td>r4 (or higher)</td>

    </tr>

    <tr>

      <td>ADT Plugin</td>

      <td>0.9.7 (or higher)</td>

    </tr>

  </table>

  <p>You can download the tools and platforms using the <em>Android SDK and AVD Manager</em>, as

  described in <a href="{@docRoot}sdk/adding-components.html">Adding SDK Components</a>.</p>

  <h3 id="considerations">Development considerations</h3>

  <p>As you develop your library project and dependent applications, keep the points listed below

  in mind:</p>

  <ul>

  <li><p><strong>Resource conflicts</strong></p>

  <p>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.</p>

  </li>

  <li><p><strong>Use prefixes to avoid resource conflicts</strong></p>

  <p>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).</p></li>

  <li><p><strong>You cannot export a library project to a JAR file</strong></p>

  <p>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.</p></li>

  <li><p><strong>One library project cannot reference another</strong></p>

  <p>A library cannot depend on another library</p></li>

  <li><p><strong>A library project can include a JAR library</strong></p>

  <p>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.</p></li>

  <li><p><strong>A library project can depend on an external JAR library</strong></p>

  <p>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 in their manifest

  files, in a <a href=

  "{@docRoot}guide/topics/manifest/uses-library-element.html"><code>&lt;uses-library&gt;</code></a>

  element.</p></li>

  <li><p><strong>Library project cannot include AIDL files</strong></p>

  <p>The tools do not support the use of AIDL files in a library project. Any AIDL files used by an

  application must be stored in the application project itself.</p></li>

  <li> <p><strong>Library projects cannot include raw assets</strong></p>

  <p>The tools do not support the use of raw asset files (saved in the <code>assets/</code> directory)

  in a library project. Any asset resources

  used by an application must be stored in the <code>assets/</code> directory of the application

  project itself. However, resource files saved in the

  <code>res/</code> directory are supported.</p></li>

  <li><p><strong>Platform version must be lower than or equal to the Android project</strong></p>

  <p>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 <a href=

  "{@docRoot}guide/appendix/api-levels.html">API level</a> that is the same as &mdash; 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 not 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.</p></li>

  <li> <p><strong>No restriction on library package names</strong></p>

  <p>There is no requirement for the package name of a library to be the same as that of

  applications that use it.</p></li>

  <li><p><strong>Each library project creates its own R class </strong></p>

  <p>When you build the dependent application project, library projects are compiled and

  merged with the application project. Each library has its own <code>R</code> class, named according

  to the library's package name. The <code>R</code> class generated from main

  project and the library project is created in all the packages that are needed including the main

  project's package and the libraries' packages.</p></li>

  <li><p><strong>Library project storage location</strong></p>

  <p>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. What is important is that the main

  project can reference the library project through a relative link.</p></li>

  </ul>

  <h2 id="TestProjects">Test Projects</h2>

  <p>Test projects contain Android applications that you write using the 

  <a href="{@docRoot}guide/topics/testing/index.html">Testing and

  Instrumentation framework</a>. The framework is an extension of the JUnit test framework and adds

  access to Android system objects. The file structure of a test project is the same as an

  Android project.</p>

  <dl>

    <dt><code>src/</code></dt>

    <dd>Includes your test source files. Test projects do not require an Activity <code>.java</code>

    file, but can include one.</dd>

    <dt><code>gen/</code></dt>

    <dd>This contains the Java files generated by ADT, such as your <code>R.java</code> file and

    interfaces created from AIDL files.</dd>

    <dt><code>assets/</code></dt>

    <dd>This is empty. You can use it to store raw asset files.</dd>

    <dt><code>res/</code></dt>

    <dd>A folder for your application resources, such as drawable files, layout files, string

    values, etc. See <a href="{@docRoot}guide/topics/resources/index.html">Application

    Resources</a>.</dd>

    <dt><code>AndroidManifest.xml</code></dt>

    <dd>The Android Manifest for your project. See <a href=

    "{@docRoot}guide/topics/manifest/manifest-intro.html">The AndroidManifest.xml File</a>. Test

    Projects have a special <a href=

    "{@docRoot}guide/topics/manifest/instrumentation-element.html">

    <code>&lt;instrumentation&gt;</code></a>

    element that connects the test project with the application project.</dd>

    <dt><code>build.properties</code></dt>

    <dd>Customizable properties for the build system. You can edit this file to override default

    build settings used by Ant and provide a pointer to your keystore and key alias so that the

    build tools can sign your application when built in release mode.</dd>

    <dt><code>build.xml</code></dt>

    <dd>The Ant build file for your project.</dd>

    <dt><code>default.properties</code></dt>

    <dd>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".</dd>

  </dl>For more information, see the <a href=

  "{@docRoot}guide/developing/testing/index.html">Testing</a> section.

  <h2>Testing a library project</h2>

  <p>There are two recommended ways of setting up testing on code and resources in a library

  project:</p>

  <ul>

    <li>You can set up a <a href="{@docRoot}guide/developing/testing/testing_otheride.html">test

    project</a> that instruments an application project that depends on the library project. You

    can then add tests to the project for library-specific features.</li>

    <li>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.</li>

  </ul>

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