The Gradle build system in Android Studio makes it easy to include external binaries or other library modules to your build as dependencies. The dependencies can be located on your machine or in a remote repository, and any transitive dependencies they declare are automatically included as well.

This page describes how to use dependencies with your Android project, including details about behaviors and configurations that are specific to the Android plugin for Gradle. For a deeper conceptual guide to Gradle dependencies, you should also see the ​​Gradle guide for dependency management​​​—but remember that your Android project must use only the ​​dependency configurations​​ defined on this page.

Dependency types

To add a dependency to your project, specify a dependency configuration such as ​​compile​​ in the ​​dependencies​​ block of your ​​build.gradle​​For example, the following ​​build.gradle​​

apply plugin: 'com.android.application'

android { ... }
dependencies {
    // Dependency on a local library module
    compile project(":mylibrary")

    // Dependency on local binaries
    compile fileTree(dir: 'libs', include: ['*.jar'])

    // Dependency on a remote binary
    compile 'com.example.android:app-magic:12.3'
}

Each of these request a different kind of dependency as follows:

Local library module dependency


compile project(':mylibrary')


This declares a dependency on an 

​​Android library module​​ named "mylibrary" (this name must match the library name defined as an 

​​include​​ in your 

​​​settings.gradle​​​ file). It requires the build system to compile the library module with your app module and include the resulting AAR file in your APK.


Local binary dependency


compile fileTree(dir: 'libs', include: ['*.jar'])

Because Gradle reads paths relative to the ​​build.gradle​​ file, this tells the build system to add all JAR files inside your project's​​module_name/libs/​​

Alternatively, you specify individual files as follows:

compile files('libs/foo.jar', 'libs/bar.jar')

Remote binary dependency


compile 'com.example.android:app-magic:12.3'

This is actually shorthand for the following:

compile group: 'com.example.android', name: 'app-magic', version: '12.3'

This declares a dependency on version 12.3 of the "app-magic" library, inside the "code.example.android" namespace group.

Note: Remote dependencies like this require that you declare the appropriate ​​remote repositories​​ where Gradle should look for the library. If the library does not already exist locally, Gradle pulls it from the remote site when the build requires it (such as when you click Sync Project with Gradle Files 

Android添加构建依赖项Add Build Dependencies_Gradle

 or when you run a build).

Library dependency configurations

Inside the ​​dependencies​​ block, you can declare a library dependency using one of several different dependency configurations (such as ​​compile​​Note: Although the ​​Java Plugin for Gradle​​ offers dependency configurations that are similar to those defined below, you cannot use them in your Android projects—only the following configurations are compatible with the Android plugin for Gradle.

If you're using Android plugin for Gradle 3.0.0 or higher, you should use the new ​​implementation​​, ​​api​​, ​​compileOnly​​, and ​​runtimeOnly​​ dependency configurations. They work similarly to the configurations described below, but they improve build speeds on multi-module projects by allowing you to restrict whether Gradle transitively exports a dependency to other modules. To learn more, read ​​​Use the new dependency configurations​​​.​​compile​​

Gradle adds the dependency to the compilation classpath and to the APK. ​​apk​​

Note: You can use ​​apk​​

​​provided​​

Gradle adds the dependency to the compilation classpath only (it is not added to the APK). This is useful when you're creating an  ​​​Android library module​​​ and you need the dependency during compilation, but it's optional to have present at runtime. That is, if you use this configuration, then your library module must include a runtime condition to check whether the dependency is available, and then gracefully change its behavior so it can still function if it's not provided. This helps reduce the size of the final APK by not adding transient dependencies that aren't critical. You might also use this in an Android app module when your dependency is a JAR file that you need at compile-time and that you can safely assume is already available at runtime (and therefore you don't want to copy it into your APK). Or perhaps you want to compile against the JAR specified with the ​​provided​​ configuration, but use the ​​apk​​Note: If you're creating an Android app module, you cannot use ​​provided​​

The above configurations apply to your project's main source set, which is applied to all build variants. If you instead want to declare a dependency for only a specific ​​build variant​​​ source set or for a ​​testing source set​​, you must capitalize the configuration name and prefix it with the name of the build variant or testing source set.

For example, to add a ​​compile​​

dependencies {
    freeCompile 'com.google.firebase:firebase-ads:9.8.0'
}

However, if you want to add a dependency for a variant that combines a product flavor and a build type, then you must initialize the configuration name in the ​​configurations​​ block. The following sample adds an ​​apk​​

configurations {
    // Initializes a placeholder for the freeDebugApk dependency configuration.
    freeDebugApk {}
}

dependencies {
    freeDebugApk fileTree(dir: 'libs', include: ['*.jar'])
}

To add ​​compile​​

dependencies {
    // Adds a remote binary dependency only for local tests.
    testCompile 'junit:junit:4.12'

    // Adds a remote binary dependency only for the instrumented test APK.
    androidTestCompile 'com.android.support.test.espresso:espresso-core:2.2.2'
}

And if your ​​library module provides multiple variants​​, you can add different library variants to different app variants like this:

dependencies {
  // Adds the 'debug' varaint of the library to the debug varaint of the app
  debugCompile project(path: ':my-library-module', configuration: 'debug')

  // Adds the 'release' varaint of the library to the release varaint of the app
  releaseCompile project(path: ':my-library-module', configuration: 'release')
}

If you're using Android plugin for Gradle 3.0.0 or higher, the plugin automatically matches each variant of your app with corresponding variants of its local library module dependencies for you. That is, you should no longer target specific variants of local module dependencies, as shown above. To learn more, read ​​Use variant-aware dependency management​​.

For more information, see ​​Java Plugin dependency management​​.

Remote repositories

When your dependency is something other than a local library or file tree, Gradle looks for the files in whichever online repositories are specified in the​​repositories​​ block of your ​​build.gradle​​By default, new Android Studio projects declare JCenter as the repository location in the project's top-level ​​build.gradle​​

allprojects {
    repositories {
        jcenter()
    }
}

If you want something from the Maven central repository, then add ​​mavenCentral()​​, or for a local repository use ​​mavenLocal()​​:

allprojects {
    repositories {
        jcenter()
        mavenCentral()
        mavenLocal()
    }
}

Or you can declare specific Maven or Ivy repositories as follows:

allprojects {
    repositories {
        maven {
            url "https://repo.example.com/maven2"
        }
        maven {
            url "file://local/repo/"
        }
        ivy {
            url "https://repo.example.com/ivy"
        }
    }
}

For more information, see the ​​Gradle Repositories guide​​.

Google's Maven repository

The most recent versions of the following Android libraries are available from Google's Maven repository:

You can see all available artifacts at ​​Google's Maven repository index​​​ (see below for ​​programmatic access​​).

To add one of these libraries to your build, include Google's Maven repository in your top-level ​​build.gradle​​

allprojects {
    repositories {
        google()

        // If you're using a version of Gradle lower than 4.1, you must instead use:
        // maven {
        //     url 'https://maven.google.com'
        // }
        // An alternative URL is 'https://dl.google.com/dl/android/maven2/'
    }
}

Then add the desired library to your module's ​​dependencies​​ block. For example, the ​​​appcompat library​​ looks like this:

dependencies {
    compile 'com.android.support:appcompat-v7:27.1.1'
}

However, if you're trying to use an older version of the above libraries and your dependency fails, then it's not available in the Maven repository and you must instead get the library from the offline repository.

Programmatic access

For programmatic access to Google's Maven artifacts, you can get an XML list of artifact groups from ​​maven.google.com/master-index.xml​​. Then, for any group, you can view its library names and versions at:

maven.google.com/group_path/group-index.xml

For example, libraries in the android.arch.lifecycle group are listed at ​​maven.google.com/android/arch/lifecycle/group-index.xml​​.

You can also download the POM and JAR files at:

maven.google.com/group_path/library/version/library-version.ext

For example: ​​maven.google.com/android/arch/lifecycle/compiler/1.0.0/compiler-1.0.0.pom​​.

Offline repository from SDK Manager

For libraries not available from the Google Maven repository (usually older library versions), you must download the offline Google Repository package from the ​​SDK Manager​​.

Then you can add these libraries to your ​​dependencies​​The offline libraries are saved in ​​android_sdk/extras/​​.

Dependency order

The order in which you list your dependencies indicates the priority for each: the first library is higher priority than the second, the second is higher priority than the third, and so on. This order is important in the event that ​​resources are merged​​​ or ​​manifest elements are merged​​ into your app from the libraries.

For example, if your project declares the following:

  • Dependency on 

​​LIB_A​​

  •  and 

​​LIB_B​​

  • And 

​​LIB_A​​

  •  depends on 

​​LIB_C​​

  •  and 

​​LIB_D​​

  • And 

​​LIB_B​​

  •  also depends on 

​​LIB_C​​

Then, the flat dependency order will be as follows:

​​LIB_A​​​​LIB_D​​​​LIB_B​​​​LIB_C​​This ensures that both ​​LIB_A​​ and ​​LIB_B​​ can override ​​LIB_C​​; and ​​LIB_D​​ is still higher priority than ​​LIB_B​​ because ​​LIB_A​​ (which depends on it) has higher priority than ​​LIB_B​​.

For more information about how manifests from different project sources/dependencies are merged, see ​​Merge Multiple Manifest Files​​.

View the dependency tree

Some direct dependencies may have dependencies of their own. These are called transitive dependencies. Rather than requiring you to manually declare each transitive dependency, Gradle automatically gathers and adds them for you. To visualize both the direct and transitive dependencies of your project, the Android plugin for Gradle provides a Gradle task that generates a dependency tree for each ​​build variant​​​ and ​​testing source set​​.

To run the task, proceed as follows:

  1. Select View > Tool Windows > Gradle (or click Gradle in the tool windows bar).
  2. Expand AppName and double-click androidDependencies. After Gradle executes the task, the Run window should open to display the output.

The following sample output shows the dependency tree for the debug build variant, and includes the local library module dependency and remote dependency from the previous example.

Executing tasks: [androidDependencies]:app:androidDependencies debug /** * Both the library module dependency and remote binary dependency are listed * with their transitive dependencies. */ +--- MyApp:mylibrary:unspecified | \--- com.android.support:appcompat-v7:27.1.1 | +--- com.android.support:animated-vector-drawable:27.1.1 | | \--- com.android.support:support-vector-drawable:27.1.1 | | \--- com.android.support:support-v4:27.1.1 | | \--- LOCAL: internal_impl-27.1.1.jar | +--- com.android.support:support-v4:27.1.1 | | \--- LOCAL: internal_impl-27.1.1.jar | \--- com.android.support:support-vector-drawable:27.1.1 | \--- com.android.support:support-v4:27.1.1 | \--- LOCAL: internal_impl-27.1.1.jar \--- com.android.support:appcompat-v7:27.1.1 +--- com.android.support:animated-vector-drawable:27.1.1 | \--- com.android.support:support-vector-drawable:27.1.1 | \--- com.android.support:support-v4:27.1.1 | \--- LOCAL: internal_impl-27.1.1.jar +--- com.android.support:support-v4:27.1.1 | \--- LOCAL: internal_impl-27.1.1.jar \--- com.android.support:support-vector-drawable:27.1.1 \--- com.android.support:support-v4:27.1.1 \--- LOCAL: internal_impl-27.1.1.jar ...

For more information about managing dependencies in Gradle, see ​​Dependency Management Basics​​ in the Gradle User Guide.