Overview of Play Feature Delivery

Google Play’s app serving model uses Android App Bundles to generate and serve optimized APKs for each user’s device configuration, so users download only the code and resources they need to run your app.

Play Feature Delivery uses advanced capabilities of app bundles, allowing certain features of your app to be delivered conditionally or downloaded on demand. To do that, first you need to separate these features from your base app into feature modules.

Feature module build configuration

When you create a new feature module using Android Studio, the IDE applies the following Gradle plugin to the module’s build.gradle file.

// The following applies the dynamic-feature plugin to your feature module.
// The plugin includes the Gradle tasks and properties required to configure and build
// an app bundle that includes your feature module.

plugins {
  id 'com.android.dynamic-feature'
}

Many of the properties available to the standard application plugin are also available to your feature module. The following sections describe the properties you should and shouldn’t include in your feature module’s build configuration.

What not to include in the feature module build configuration

Because each feature module depends on the base module, it also inherits certain configurations. So, you should omit the following in the feature module’s build.gradle file:

• Signing configurations: App bundles are signed using signing configurations that you specify in the base module.
• The minifyEnabled property: You can enable code shrinking for your entire app project from only the base module’s build configuration. So, you should omit this property from feature modules. You can, however, specify additional ProGuard rules for each feature module.
• versionCode and versionName: When building your app bundle, Gradle uses app version information that the base module provides. You should omit these properties from your feature module’s build.gradle file.

Establish a relationship to the base module

When Android Studio creates your feature module, it makes it visible to the base module by adding the android.dynamicFeatures property to the base module’s build.gradle file, as shown below:

// In the base module’s build.gradle file.
android {
    ...
    // Specifies feature modules that have a dependency on
    // this base module.
    dynamicFeatures = [":dynamic_feature", ":dynamic_feature2"]
}

Additionally, Android Studio includes the base module as a dependency of the feature module, as shown below:

// In the feature module’s build.gradle file:
...
dependencies {
    ...
    // Declares a dependency on the base module, ':app'.
    implementation project(':app')
}

Specify additional ProGuard rules

Although only the base module’s build configuration may enable code shrinking for your app project, you can provide custom ProGuard rules with each feature module using the proguardFiles property, as shown below.

android.buildTypes {
     release {
         // You must use the following property to specify additional ProGuard
         // rules for feature modules.
         proguardFiles 'proguard-rules-dynamic-features.pro'
     }
}

Note that these ProGuard rules are merged with those from other modules (including the base module) at build time. So, while each feature module may specify a new set of rules, those rules apply to all modules in the app project.

Deploy your app

While you're developing your app with support for feature modules, you can deploy your app to a connected device like you normally would by selecting Run > Run from the menu bar (or by clicking Run in the toolbar).

If your app project includes one or more feature modules, you can choose which features to include when deploying your app by modifying your existing run/debug configuration as follows:

1. Select Run > Edit Configurations from the menu bar.
2. From the left panel of the Run/Debug Configurations dialog, select your desired Android App configuration.
3. Under Dynamic features to deploy in the General tab, check the box next to each feature module you want to include when deploying your app.
4. Click OK.

By default, Android Studio doesn't deploy your app using app bundles to deploy your app. Instead, the IDE builds and installs APKs to your device that are optimized for deployment speed, rather than APK size. To configure Android Studio to instead build and deploy APKs and instant experiences from an app bundle, modify your run/debug configuration.

Use feature modules for custom delivery

A unique benefit of feature modules is the ability to customize how and when different features of your app are downloaded onto devices running Android 5.0 (API level 21) or higher. For example, to reduce the initial download size of your app, you can configure certain features to be either downloaded as needed on demand or only by devices that support certain capabilities, such as the ability to take pictures or support augmented reality features.

Although you get highly optimized downloads by default when you upload your app as an app bundle, the more advanced and customizable feature delivery options require additional configuration and modularization of your app’s features using feature modules. That is, feature modules provide the building blocks for creating modular features that you can configure to each be downloaded as needed.

Consider an app that allows your users to buy and sell goods in an online marketplace. You can reasonably modularize each of the following functionalities of the app into separate feature modules:

• Account login and creation
• Browsing the marketplace
• Placing an item for sale
• Processing payments

The table below describes the different delivery options that feature modules support, and how they might be used to optimize the initial download size of the sample marketplace app.

Building a URI for a resource

If you want to access a resource stored in a feature module using a URI, here’s how to generate a feature module resource URI using Uri.Builder():

val uri = Uri.Builder()
                .scheme(ContentResolver.SCHEME_ANDROID_RESOURCE)
                .authority(context.getPackageName()) // Look up the resources in the application with its splits loaded
                .appendPath(resources.getResourceTypeName(resId))
                .appendPath(String.format("%s:%s",
                  resources.getResourcePackageName(resId), // Look up the dynamic resource in the split namespace.
                  resources.getResourceEntryName(resId)
                  ))
                .build()

String uri = Uri.Builder()
                .scheme(ContentResolver.SCHEME_ANDROID_RESOURCE)
                .authority(context.getPackageName()) // Look up the resources in the application with its splits loaded
                .appendPath(resources.getResourceTypeName(resId))
                .appendPath(String.format("%s:%s",
                  resources.getResourcePackageName(resId), // Look up the dynamic resource in the split namespace.
                  resources.getResourceEntryName(resId)
                  ))
                .build().toString();

Each part of the path to the resource is constructed at run time, ensuring that the correct namespace is generated after the split APKs have been loaded.

As an example of how the URI is generated, suppose you have an app and feature modules with these names:

• App package name: com.example.my_app_package
• Feature's resources package name: com.example.my_app_package.my_dynamic_feature

If the resId in the code snippet above refers to a raw file resource named “my_video” in your feature module, then the Uri.Builder() code above would output the following:

android.resource://com.example.my_app_package/raw/com.example.my_app_package.my_dynamic_feature:my_video

This URI can then be used by your app to access the feature module’s resource.

To validate the paths in your URI, you can use the APK Analyzer to inspect your feature module APK and determine the package name:

Figure 2. Use the APK Analyzer to inspect the package name in a compiled resource file.

Considerations for feature modules

With feature modules, you can improve build speed and engineering velocity and extensively customize delivery of your app's features to reduce your app's size. However, there are some constraints and edge cases to keep in mind when using feature modules:

• Installing 50 or more feature modules on a single device, via conditional or on-demand delivery, might lead to performance issues. Install-time modules, which are not configured as removable, are automatically included in the base module and only count as one feature module on each device.
• Limit the number of modules you configure as removable for install-time delivery to 10 or fewer. Otherwise, the download and install time of your app might increase.
• Only devices running Android 5.0 (API level 21) and higher support downloading and installing features on demand. To make your feature available to earlier versions of Android, enable Fusing when you create a feature module.
• Enable SplitCompat, so that your app has access to downloaded feature modules that are delivered on demand.
• Feature modules should not specify activities in their manifest with android:exported set to true. That's because there's no guarantee that the device has downloaded the feature module when another app tries to launch the activity. Additionally, your app should confirm that a feature is downloaded before trying to access its code and resources. To learn more, read Manage installed modules.
• Because Play Feature Delivery requires you to publish your app using an app bundle, make sure that you're aware of app bundle known issues.

Feature module manifest reference

When creating a new feature module using Android Studio, the IDE includes most of the manifest attributes that the module requires to behave like a feature module. Additionally, some attributes are injected by the build system at compile time, so you needn’t specify or modify them yourself. The following table describes the manifest attributes that are important to feature modules.

Additional resources

To learn more about using feature modules, try the following resources.

Blog posts

• New features to help you develop, release, and grow your business on Google Play
• The latest Android App Bundle updates including the additional languages API
• Patchwork Plaid — A modularization story

Videos

• Customizable Delivery with the App Bundle and Easy Sharing of Test Builds
• New Tools to Optimize Your App's Size and Boost Installs on Google Play