Prepare for release

This page describes the properties and options you should set to prepare your library project for publication using the Android Gradle plugin (AGP). Even if you have already set some of these properties at the outset of creating your library, we recommend reviewing the following guidance to optimize your settings.

Choose a namespace

Android libraries need to declare a namespace so that they can generate a unique R class when their resources are compiled. This namespace should closely match the library’s root class package to avoid confusion when users import regular classes from the library as well as its R class.

Starting with AGP 7.0, you can set the namespace in the app’s build.gradle file as shown in the following code example:

android {
  namespace = 'com.example.library'
}

android {
  namespace = "com.example.library"
}

If you set the namespace in the build.gradle file and no other data needs to be specified, then the library doesn't need a manifest file. This is recommended because it removes the need to parse the manifest file during build steps and sync.

The namespace is purely a developer-facing property of the library. It has nothing to do with the application’s identity that is set using the applicationId property. In previous versions of AGP, both the applicationId property (for an app) and the namespace property (for a library) could be set using the manifest’s package attribute, which led to confusion. Note that a library project does not have an applicationId; it is a property of an application only.

Choose a minSdkVersion value

Choosing a minSdkVersion for your library is an important aspect of publishing your library. The minSdkVersion should reflect the minimum version of Android that your code can support.

Be aware of the following considerations when choosing a minSdkVersion:

• Choosing a low minSdkVersion generally allows for wider distribution of your library. A library’s code is generally not executed unless the application calls it explicitly. An application can still run on a version of Android that is lower than required by a library dependency—if the library is not essential to core app functionality—by doing runtime checks before calling the library. Therefore, setting a library’s minSdkVersion low enough that it can be embedded in apps, and called when possible, will likely help you reach more users.
• Choosing a high minSdkVersion might prevent applications from including the library. The manifest merger, which is a step in AGP that merges manifest files from the application and from its dependencies, enforces that no dependencies have a higher minSdkVersion than the application.
• Choosing a high minSdkVersion might prompt app developers to disable manifest merger safety checks, which causes issues later in the build process. Because the manifest merger prevents application projects from including libraries with a higher minSdkVersion than the app itself, app developers might disable the safety checks of the manifest merger to minimize build errors. However, this risks true incompatibility issues downstream.
• It might be necessary to choose a high minSdkVersion in special cases where a library’s manifest includes a broadcast receiver or some other mechanism by which its code is triggered automatically. In these cases, choosing a high minSdkVersion ensures that code can run. Alternatively, you can disable the automated behavior so that the app can opt in to executing the library after doing the right checks.

Note that to allow for embedding in apps, a library should use the RequiresApi annotation to indicate to its callers that they need to do runtime checks. Android Lint uses the RequiresApi information for its inspections. For more resources on using annotations to improve your API code and APIs, see Improve code inspection with annotations.

Set up AAR metadata

An Android library is packaged in the form of an Android Archive (AAR) file. AAR metadata consists of properties that help AGP consume libraries. If your library is consumed by an incompatible configuration, and AAR metadata is set up, users are presented with an error message to help them resolve the issue.

AAR metadata does not contain properties that are important at runtime and therefore are not typically found in compiled Android applications.

Choose a minCompileSdk value

Starting with version 4.1, AGP supports minCompileSdk. This indicates the minimum compileSdk that consuming projects can use. If your library contains manifest entries, or resources that make use of newer platform attributes, you probably need to set this value.

The minCompileSdk value can be set in the defaultConfig{}, productFlavors{}, and buildTypes{} blocks in the module-level build.gradle file.

android {
  defaultConfig {
    aarMetadata {
      minCompileSdk = 29
    }
  }
  productFlavors {
    foo {
      ...
      aarMetadata {
        minCompileSdk = 30
      }
    }
  }
}

android {
  defaultConfig {
    aarMetadata {
      minCompileSdk = 29
    }
  }
  productFlavors {
    register("foo") {
      ...
      aarMetadata {
        minCompileSdk = 30
      }
    }
  }
}

If you set minCompileSdk in multiple places, Gradle prioritizes the settings locations as follows during the build process:

1. buildTypes{}

2. productFlavors{}

3. defaultConfig{}

So in the above example, where minCompileSdk is defined in both defaultConfig{} and productFlavors{}, productFlavors{} is prioritized and minCompileSdk is set to 30. To learn more about how Gradle prioritizes settings when combining code and resources, see Build with source sets.

Enable test fixtures

Test fixtures are commonly used to set up the code being tested, or facilitate the tests of a component. Starting with version 7.1, AGP can create test fixtures for library projects (in addition to application and dynamic-feature projects.)

When publishing a library that others consume, consider creating test fixtures for your API. Test fixtures can be turned on in the module-level build.gradle file:

android {
  testFixtures {
    enable = true
  }
}

android {
  testFixtures {
    enable = true
  }
}

When you turn on test fixtures, Gradle automatically creates a src/testFixtures source set where you can write test fixtures. See the TestFixtures API reference doc for more options.

For more information, refer to the Gradle’s documentation about using test fixtures.