docs/html/tools/projects/index.jd

page.title=Managing Projects Overview
@jd:body

 <div id="qv-wrapper">
    <div id="qv">
      <h2>In this document</h2>

      <ol>
        <li><a href="#ProjectFiles">Android Project Files</a></li>
        <li><a href="#ApplicationModules">Android Application Modules</a></li>

        <li><a href="#LibraryModules">Library Modules</a>
          <ol>
            <li><a href="#considerations">Development considerations</a></li>
          </ol>
        </li>

        <li><a href="#TestModules">Test Modules</a></li>

        <li><a href="#testing">Testing a Library Module</a></li>
      </ol>
    </div>
  </div>

  <p>An Android <em>project</em> contains everything that defines your Android app, from app
  source code to build configurations and test code. The SDK tools require that your projects
  follow a specific structure so it can compile and package your application correctly.
  If you're using Android Studio, it takes care of all this for you.</p>

  <p>A <em>module</em> is the first level of containment within a project that encapsulates
  specific types of source code files and resources. There are several types of modules
  with a project:</p>

  <dl>

    <dt><strong>Android Application Modules</strong></dt>

    <dd>An Android Application Module is the container for your application's source code, resource
    files, and application level settings, such as the module-level build file, resource  files, and
    Android Manifest file. The application module contents are eventually
    built into the <code>.apk</code> file that gets installed on a device.</dd>

    <dt><strong>Test Modules</strong></dt>

    <dd>These modules contain code to test your application projects and are built into
    test applications that run on a device. By default, Android Studio creates the
    <em>androidTest</em> module for inserting JUnit tests. </dd>

    <dt><strong>Library Modules</strong></dt>

    <dd>These modules 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 modules cannot be installed onto a device, however, they are
    pulled into the <code>.apk</code> file at build time.</dd>


    <dt><strong>App Engine Modules</strong></dt>

    <dd>Android Studio lets you easily add a cloud backend to your application. A backend allows you
    to implement functionality such as backing up user data to the cloud, serving content to client
    apps, real-time interactions, sending push notifications through Google Cloud Messaging for
    Android (GCM), and more. App Engine modules are App Engine java Servlet Module for backend
    development, App Engine java Endpoints Module to convert server-side Java code annotations into
    RESTful backend APIs, and App Engine Backend with Google Cloud Messaging to send push notifications
    from your server to your Android devices. </dd>

  </dl>

  <p>When you use the Android development tools to create a new project and the module, 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 Android Studio or the {@code android} tool to
  generate your module. As your application grows in complexity, you might require new kinds of
  resources, directories, and files.</p>

<p class="note"><strong>Note:</strong> Project folders and files apply across the entire Android
project and override similar module file settings.</p>




  <h2 id="ProjectFiles">Android Project Files</h2>

  <p>Android Studio project files and settings provide project-wide settings that apply across all
  modules in the project.  </p>

	<dl>
   <dt><code>.idea</code></dt>

   <dd>Directory for IntelliJ IDEA settings.</dd>


   <dt><code>app</code></dt>

   <dd>Application module directories and files. </dd>


   <dt><code>build</code></dt>

   <dd>This directory stories the build output for all project modules.</dd>


    <dt><code>gradle</code></dt>

    <dd>Contains the gradler-wrapper files. </dd>


    <dt><code>.gitignore</code></dt>

    <dd>Specifies the untracked files that Git should ignore.</dd>


    <dt><code>build.gradle</code></dt>

    <dd>Customizable properties for the build system. You can edit this file to specify the default
    build settings used by the application modules and also set the location of your keystore and key alias
    so that the build tools can sign your application when building in release mode. This file is
    integral to the project, so maintain it in a source revision control system. </dd>

    <dt><code>gradle.properties</code></dt>

    <dd>Project-wide Gradle settings.</dd>


    <dt><code>gradlew</code></dt>

    <dd>Gradle startup script for Unix.</dd>


    <dt><code>gradlew.bat</code></dt>

    <dd>Gradle startup script for Windows. </dd>

   <dt><code>local.properties</code></dt>

   <dd>Customizable computer-specific properties for the build system, such as the path to the SDK
   installation. Because the content of the file is specific to the local installation of the SDK,
   the <code>local.properties</code> should not be maintained in a source revision control system. </dd>


    <dt><code><project>.iml</code></dt>

    <dd>Module file created by the IntelliJ IDEA to store module information.</dd>

    <dt><code>settings.gradle</code></dt>

    <dd>Specifies the sub-projects to build.</dd>

  </dl>


  <h2 id="ApplicationModules">Android Application Modules</h2>

  <p>Android Application Modules are the modules that eventually get built into the <code>.apk</code>
  files based on your build settings. They contain things such as application source code and resource
  files. Most code and resource files are generated for you by default, while others should be created if
  required. The following directories and files comprise an Android application module:</p>

  <dl>

    <dt><code>build/</code></dt>

    <dd>Contains build folders for the specified build variants. Stored in the main application module.</dd>


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

    <dd>Contains private libraries. Stored in the main application module.</dd>




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

    <dd>Contains your stub Activity file, which is stored at
    <code>src<em>/main/java/<namespace.applicationname>/ActivityName></em>.java</code>. All other source
    code files (such as <code>.java</code> or <code>.aidl</code> files) go here as well.</dd>

     <dl>
       <dt><code>androidTest/</code></dt>

       <dd>Contains the instrumentation tests. For more information, see the
       <a href="{@docRoot}tools/testing/index.html">Android Test documentation</a>.</dd>

       <dt><code>main/java/com.&gt;project&lt;.&gt;app&lt;</code></dt>

       <dd>Contains Java code source for the app activities.</dd>

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

       <dd>Contains native code using the Java Native Interface (JNI). For more information, see the
       <a href="{@docRoot}tools/sdk/ndk/index.html">Android NDK documentation</a>.</dd>

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

       <dd>Contains the Java files generated by Android Studio, such as your <code>R.java</code> file and
       interfaces created from AIDL files.</dd>

       <dt><code>main/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 {@link android.content.res.AssetManager}. For example, this is a good
       location for textures and game data.</dd>

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

       <dd>Contains application resources, such as drawable files, layout files, and string values
       in the following directories. 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 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 is essentially the same as
           saving them in the <code>assets/</code> directory. The only difference is how 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 define resources by XML element type. 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
           defined within the XML files 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>

      <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>

   </dl>

   <dt><code>.gitignore/</code></dt>

   <dd>Specifies the untracked files ignored by git.</dd>

   <dt><code>app.iml/</code></dt>

   <dd>IntelliJ IDEA module</dd>

   <dt><code>build.gradle</code></dt>

   <dd>Customizable properties for the build system. You can edit this file to override default
    build settings used by the manifest file and also set the location of your keystore and key alias
    so that the build tools can sign your application when building in release mode. This file is
    integral to the project, so maintain it in a source revision control system. </dd>

    <dt><code>proguard-rules.pro</code></dt>

    <dd>ProGuard settings file. </dd>


  </dl>



  <h2 id="LibraryModules">Library Module</h2>

  <div class="sidebox-wrapper">
    <div class="sidebox">
      <h2>Library module 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 module. The TicTacToeMain
      application uses code and resources from an example library module called TicTacToeLib.</p>

      <p>To download the sample applications and run them as modules in
      your environment, use the <em>Android SDK Manager</em> to download the "Samples for
      SDK API 8" (or later) module 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 module</em> is a development module that holds shared Android
    source code and resources. Other Android application modules can reference the library module
    and, at build time, include its compiled sources in their <code>.apk</code> files. Multiple
    application modules can reference the same library module and any single application module
    can reference multiple library modules.</p>

    <p class="note"><strong>Note:</strong> You need SDK Tools r14 or newer to use the new library
    module feature that generates each library module into its own JAR file.
    You can download the tools and platforms using the
    <em>Android SDK Manager</em>, as described in
    <a href="{@docRoot}tools/help/sdk-manager.html">SDK tools help</a>.</p>

    <p>If you have source code and resources that are common to multiple Android projects, you
    can move them to a library module so that it is easier to maintain across applications and
    versions. Here are some common scenarios in which you could make use of library modules:</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 module and create a
      single, reusable set of the same components in a library module.</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 module. The two
      dependent modules, with their different package names, will reference the library module
      and provide only the difference between the two application versions.</li>
    </ul>

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

    <p>However, a library module differs from a standard Android application module 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 module 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 module, the SDK tools compile the
    library into a temporary JAR file and use it in the main module, then uses 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 module 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
    modules, 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 modules to your Android application module,
    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>Library modules can reference other library modules and can import an external library
    (JAR) in the normal way.</p>

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

  <p>As you develop your library modules 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 module with those of a dependent application
  module, a given resource ID might be defined in both modules. 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 module (or is unique across all project modules).</p></li>

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

  <p>A library cannot be distributed as a binary file (such as a JAR file). This will be added in a
  future version of the SDK Tools.</p></li>

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

  <p>You can develop a library module that itself includes a JAR library; however you need to
  manually edit the dependent application modules's build path and add a path to the JAR file.</p></li>

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

  <p>You can develop a library module 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 module 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 modules 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 module. Any asset resources
  used by an application must be stored in the <code>assets/</code> directory of the application
  module 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 module</strong></p>

  <p>A library is compiled as part of the dependent application module, so the API used in the
  library module must be compatible with the version of the Android library used to compile the
  application module. In general, the library module should use an <a href=
  "{@docRoot}guide/topics/manifest/uses-sdk-element.html#ApiLevels">API level</a> that is the same as &mdash; or lower
  than &mdash; that used by the application. If the library module uses an API level that is
  higher than that of the application, the application module 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) module, for instance.</p></li>

  <li> <p><strong>No restriction on library module 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 module creates its own R class </strong></p>

  <p>When you build the dependent application modules, library modules are compiled and
  merged with the application module. 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
  module and the library module is created in all the packages that are needed including the main
  module's package and the libraries' packages.</p></li>

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

  <p>There are no specific requirements on where you should store a library module, relative to a
  dependent application module, as long as the application module can reference the library
  module by a relative link. What is important is that the main
  module can reference the library module 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}tools/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. </p>

  <p>The test projects are now automatically part of the app source folder. When a new application
  module is created, Android Studio creates the <code>src/androidTest</code> source set. This
  source set contains tests for the default configuration and is combined with the <em>debug</em>
  build type to generate a test application. </p>

  <img src="{@docRoot}images/tools/studio-androidtest-folder.png">
  <p class="img-caption"><strong>Figure 1.</strong> androidTest Folder.</p>

  <p class="note"><strong>Note:</strong> The <code>src/androidTest</code> source set may not be
  created for every type of available module template. If this source set is not created, you
  can just create it for that module.</p>

  <p>For each product flavor, create a test folder specific to that product flavor.  </p>

  <dl>
    <dt><code>src/main/</code></dt>
    <dd><code>src/androidTest/</code></dt>

    <dt><code>src/productFlavor1/</code></dt>
    <dd><code>src/testproductFlavor1/</code></dd>

    <dt><code>src/productFlavor2/</code></dt>
    <dd><code>src/testproductFlavor2/</code></dd>

  </dl>

  <p>The test manifests are always generated so a manifest in a test source set is optional.</p>

  <p>The test applications run against the <em>debug</em> build type.  This can be configured
  using the <code>testBuildType</code> property in the build file.</p>


  <p>For more information, see the
  <a href="{@docRoot}tools/testing/index.html">Testing</a> section.</p>


  <h2 id="testing">Testing a Library Module</h2>

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

  <ul>
    <li>You can set up a <a href="{@docRoot}tools/testing/testing_otheride.html">test
    module</a> that instruments an application module that depends on the library module. You
    can then add tests to the module for library-specific features.</li>

    <li>You can set up a standard application module that depends on the library and put
    the instrumentation in that module. This lets you create a self-contained module that
    contains both the tests/instrumentations and the code to test.</li>
  </ul>