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.

Delivery option Behavior Sample use-case Getting started
Install-time delivery Feature modules that don’t configure any of the delivery options described above are downloaded at app install, by default. This is an important behavior because it means that you can adopt advanced delivery options gradually. For example, you can benefit from modularizing your app’s features and enable on demand delivery only after you’ve fully implemented on demand downloads using the Play Core library.

In addition, your app can request to uninstall features at a later time. So, if you require certain features at app install, but not after that, you can reduce install size by requesting to remove the feature from the device.

If the app has certain training activities, such as an interactive guide on how to buy and sell items in the marketplace, you can include that feature at app install, by default.

However, to reduce the installed size of the app, the app can request to delete the feature after the user has completed the training.

Modularize your app using feature modules that configure no advanced delivery options.

To learn how to reduce the installed size of your app by removing certain feature modules that the user may no longer need, read Manage installed modules.

On demand delivery Allows your app to request and download feature modules as needed. If only 20% of those who use the marketplace app post items for sale, a good strategy to reduce the initial download size for the majority of users is to make the functionality for taking pictures, including an item description, and placing an item for sale available as an on demand download. That is, you can configure the feature module for the selling functionality of the app to be downloaded only when a user shows interest in placing items for sale onto the marketplace.

Additionally, if the user no longer sells items after a certain period of time, the app can reduce its installed sized by requesting to uninstall the feature.

Create a feature module and configure on demand delivery. Your app can then use the Play Core library to request to download the module on demand.
Conditional delivery Allows you to specify certain user device requirements, such as hardware features, locale, and minimum API level to determine whether a modularized feature is downloaded at app install. If the marketplace app has global reach, you might need to support payment methods that are popular in only certain regions or locals. In order to reduce the initial app download size, you can create separate feature modules for processing certain types of payment methods and have them installed conditionally on a user’s device based on their registered locale. Create a feature module and configure conditional delivery.
Instant delivery Google Play Instant allows users to interact with your app without needing to install the app on their device. Instead, they can experience your app through the "Try Now" button on the Google Play Store or a URL that you create. This form of delivering content makes it easier for you to increase engagement with your app.

With instant delivery, you can utilize Google Play Instant to allow your users to instantly experience certain features of your app without installation.

Consider a game that include the first few levels of the game in a lightweight feature module. You can instant-enable that module so that users can instantly experience the game through a URL link or “Try Now" button, without app installation. Create a feature module and configure instant delivery. Your app can then use the Play Core library to request to download the module on demand.

Keep in mind, modularizing your app features using feature modules is only the first step. To support Google Play Instant, the download size of the base module of your app and a given instant-enabled feature must satisfy strict size restrictions. To learn more, read Enable instant experiences by reducing app or game size.

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():

Kotlin

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()

Java

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:

A screenshot of the APK Analyzer inspecting the contents of a compiled resource file.

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.

Attribute Description
<manifest
...
This is your typical <manifest> block.
xmlns:dist="http://schemas.android.com/apk/distribution" Specifies a new dist: XML namespace that’s described further below.
split="split_name" When Android Studio builds your app bundle, it includes this attribute for you. So, you should not include or modify this attribute yourself.

Defines the name of the module, which your app specifies when requesting an on demand module using the Play Core Library.

How Gradle determines the value for this attribute:

By default, when you create a feature module using Android Studio, The IDE uses what you specify as its Module name to identify the module as a Gradle subproject in your Gradle settings file.

When you build your app bundle, Gradle uses the last element of the subproject path to inject this manifest attribute in the module’s manifest. For example, if you create a new feature module in the MyAppProject/features/ directory and specified "dynamic_feature1" as its Module name, the IDE adds ':features:dynamic_feature1' as a subproject in your settings.gradle file. When building your app bundle, Gradle then injects <manifest split="dynamic_feature1"> in the module’s manifest.

android:isFeatureSplit="true | false"> When Android Studio builds your app bundle, it includes this attribute for you. So, you should not include or modify this attribute manually.

Specifies that this module is a feature module. Manifests in the base module and configuration APKs either omit this attribute or set it to false.

<dist:module This new XML element defines attributes that determine how the module is packaged and distributed as APKs.
dist:instant="true | false" Specifies whether the module should be available through Google Play Instant as an instant experience.

If your app includes one or more instant-enabled feature modules, you must also instant-enable the base module. When using Android Studio 3.5 or higher, the IDE does this for you when you create an instant-enabled feature module.

You can’t set this XML element to true while also setting <dist:on-demand/>. However, you can still request on demand downloads of your instant-enabled feature modules as instant experiences using the Play Core Library. When a user downloads and installs your app, the device downloads and installs your app's instant-enabled feature modules, along with the base APK, by default.

dist:title="@string/feature_name" Specifies a user-facing title for the module. For example, the device may display this title when it requests download confirmation.

You need to include the string resource for this title in the base module’s module_root/src/source_set/res/values/strings.xml file.

<dist:fusing dist:include="true | false" />
</dist:module>
Specifies whether to include the module in multi-APKs that target devices running Android 4.4 (API level 20) and lower.

Additionally, when you use bundletool to generate APKs from an app bundle, only feature modules that set this property to true are included in the universal APK—which is a monolithic APK that includes code and resources for all device configurations your app supports.

<dist:delivery> Encapsulates options that customizes module delivery, as shown below. Keep in mind, each feature module must configure only one type of these custom delivery options.
<dist:install-time> Specifies that the module should be available at install time. This is the default behavior for feature modules that do not specify another type of custom delivery option.

To learn more about install-time downloads, read Configure install-time delivery.

This node is can also specify conditions that limit the module to devices that meet certain requirements, such as device features, user country, or minimum API level. To learn more, read Configure conditional delivery.

<dist:removable dist:value="true | false" />

When unset or set to false, bundletool will fuse install-time modules into the base module when generating split APKs from the bundle. Because there will be fewer split APKs as a result of fusing, this setting may improve your app's performance.

When removable is set to true: install-time modules will not be fused into the base module. Set to true if you want to uninstall modules in the future. However, configuring too many modules to be removable might increase the install time for your app.

Defaults to false. It's only necessary to set this value in the manifest if you want to disable fusing for a feature module.

Note: This feature is only available when using Android Gradle plugin 4.2 or when using bundletool v1.0 from the command line.

</dist:install-time>  
<dist:on-demand/> Specifies that the module should be available as an on demand download. That is, the module is not available at install time, but your app may request to download it later.

To learn more about on demand downloads, read Configure on demand delivery.

</dist:delivery>
<application
android:hasCode="true | false">
...
</application>
If the feature module generates no DEX files—that is, it contains no code that is later compiled into the DEX file format—you must do the following (otherwise, you may get runtime errors):
  1. Set android:hasCode to "false" in the feature module's manifest.
  2. Add the following to your base module's manifest:
    <application
      android:hasCode="true"
      tools:replace="android:hasCode">
      ...
    </application>
    

Additional resources

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

Blog posts

Videos