About Dynamic Delivery

Google Play’s app serving model, called Dynamic Delivery, uses Android AppBundles to generate and serve optimized APKs for each user’sdevice configuration, so users download only the code and resources they need torun your app. You no longer have to build, sign, and manage multiple APKs tosupport different devices, and users get smaller, more optimized downloads.

Most app projects won’t require much effort to build app bundles that supportserving optimized split APKs with Dynamic Delivery. For example,if you already organize your app’s code andresourcesaccording to established conventions, simply build signed Android AppBundles using Android Studio or usingthe command line, and upload them to GooglePlay. Dynamic Delivery then becomes an automaticbenefit.

To support advanced capabilities of Dynamic Delivery, such as configuringcertain features of your app to be delivered conditionally or downloaded ondemand, read the section on how to customize featuredelivery.

Dynamic Delivery with split APKs

A fundamental component of Dynamic Delivery is the split APK mechanismavailable on Android 5.0 (API level 21) and higher. Split APKs are verysimilar to regular APKs—they include compiled DEX bytecode, resources, and anAndroid manifest. However, the Android platform is able to treat multipleinstalled split APKs as a single app. That is, you can install multiple splitAPKs that have access to common code and resources, and appear as oneinstalled app on the device.

The benefit of split APKs is the ability to break up a monolithic APK—that is,an APK that includes code and resources for all features and deviceconfigurations your app supports—into smaller, discrete packages that areinstalled on a user’s device as required.

For example, one split APK may include the code and resources for anadditional feature that only a few of your users need, while another split APKincludes resources for only a specific language or screen density. Each ofthese split APKs is downloaded and installed when the user requests itor it’s required by the device.

The following describes the different types of APKs that may be installedtogether on a device to form your full app experience. You’ll learn how toconfigure your app project to support these APKs in later sections on this page.

• Base APK: This APK contains code and resources that all other splitAPKs can access and provides the basic functionality for your app. When auser requests to download your app, this APK is downloaded and installedfirst. That’s because only the base APK’s manifest contains a fulldeclaration of your app’s services, content providers,permissions, platform version requirements, and dependencies on systemfeatures. Google Play generates the base APK for your app from yourproject’s app (or base) module. If you are concerned with reducing your app’sinitial download size, it’s important to keep in mind that all code andresources included in this module are included in your app’s base APK.
• Configuration APKs: Each of these APKs includes native libraries andresources for a specific screen density, CPU architecture, or language.When a user downloads your app, their device downloads and installs onlythe configuration APKs that target their device. Each configuration APKis a dependency of either a base APK or dynamic feature APK. That is,they are downloaded and installed along with the APK they provide codeand resources for. Unlike the base and dynamic feature modules, you don'tcreate a separate module for configuration APKs. If you use standard practicesto organize alternative, configuration-specific resourcesfor your base and dynamic feature modules, Google Play automaticallygenerates configuration APKs for you.
• Dynamic feature APKs: Each of these APKs contains code and resources for afeature of your app that you modularize using dynamic feature modules. ThroughDynamic Delivery, you can then customize how and when that feature is downloadedonto a device. For example, using the Play CoreLibrary, dynamic APKsmay be installed on demand after the base APK is installed on the device toprovide additional functionality to the user. Consider a chat app that downloadsand installs the ability to capture and send photos only when the user requeststo use that functionality. Because dynamic features may not be available atinstall time, you should include any common code and resources in the base APK.That is, your dynamic feature should assume that code and resources of only thebase APK are available at install time. Google Play generates dynamic featureAPKs for your app from your project’s dynamic feature modules.
  Consider an app with three dynamic feature modules and support for multipledevice configurations. Figure 1 below illustrates what the dependency tree forthe app’s various APKs may look like. Note that the base APK forms the head ofthe tree, and all other APKs depend on the base APK. (If you're curious abouthow the modules for these APKs are represented in an Android App Bundle,see The Android App Bundle format.)

Figure 1. Dependency tree for an app served using split APKs

Keep in mind, you don’t need to build these APKs yourself—Google Play does itfor you using a single signed app bundle you build with Android Studio. Tolearn more about the app bundle format and how to build one, go toBuild, deploy, and upload Android App Bundles.

Devices running Android 4.4 (API level 19) and lower

Because devices running Android 4.4 (API level 19) and lower don’t supportdownloading and installing split APKs, Google Play instead serves thosedevices a single APK, called a multi-APK, that’s optimized for the device'sconfiguration. That is, multi-APKs represent your full app experience but do notinclude unnecessary code and resources—such as those for other screen densitiesand CPU architectures.

They do, however, include resources for all languages thatyour app supports. This allows, for example, users to change your app'spreferred language setting without having to download a different multi-APK.

Multi-APKs do not have the ability to later download dynamic features moduleson demand. To include a dynamic module in this APK, you must either disableOn-demand or enable Fusing whencreating the dynamic feature module.

Keep in mind, with Dynamic Delivery, you don't need to build, sign,upload, and manage APKs for each device configuration your app supports. Youstill build and upload only a single app bundle for your entire app, and GooglePlay takes care of the rest for you. So whether or not you plan to supportdevices running Android 4.4 or lower, Dynamic Delivery provides a flexibleserving mechanism for both you and your users.

Modularize your app

Modularizing your app is the process of separating logical components of yourapp project into discrete modules.

Reorganizing your app’s functionality into these discrete components takescareful consideration and time. However, modularization provides your projectwith the following benefits:

• Develop in parallel: By separating logical components of your app intomodules, different teams or individuals in your organization can take ownershipof each module and work on them with fewer merge conflicts or disruptions toother teams. Additionally, if you have logic that’s used in various parts ofyour app, you can use library modules) to promote code reuse andencapsulation.
• Improve build times: Build systems, such as the Android Studio buildsystem using Gradle, are optimized for projects that are organized intomodules. For example, if you enable Gradle’s parallel projectexecutionoptimization on a workstation includes a multi-core processor, the buildsystem is able to build multiple modules in parallel and significantlyreduce build times. The more modular your project is, the more significantthe build performance improvement becomes.
• Customize feature delivery: Modularizing your app’s features as dynamicfeature modules is a requirement to take advantage of Dynamic Delivery’s customdelivery options, such as on demand, conditional, andinstant delivery. Creating on demand dynamic features requires more effort andpossible refactoring of your app. So, consider carefully which of your app’sfeatures would benefit the most from being modularized into dynamic featuresand benefiting from custom delivery options.
  Modularizing your project by app features takes time and consideration to doproperly. When you do decide to begin modularizing your app, you should firstconfigure your base modulewith the properties necessary to support modular features. Then, you cangradually modularize your app’s features without changing the current behaviorof your app by configuring dynamic feature modules for at-installdelivery.

Use dynamic feature modules for custom delivery

A unique benefit of Dynamic Delivery is the ability to customize how and whendifferent 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 ofyour app, you can configure certain features to be either downloaded as neededon demand or only by devices that support certain capabilities, such as theability to take pictures or support augmented reality features.

Although you get highly optimized downloads by default when you upload your appas an app bundle, the more advanced and customizable feature delivery optionsrequire additional configuration and modularization of your app’s features usingdynamic feature modules. That is, dynamic feature modules provide the buildingblocks for creating modular features that you can configure to each bedownloaded as needed.

Consider an app that allows your users to buy and sell goods in an onlinemarketplace. You can reasonably modularize each of the following functionalitiesof the app into separate dynamic 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 dynamic featuremodules support, and how they might be used to optimize the initial downloadsize of the sample marketplace app.

Dynamic feature module manifest

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

<application
  android:hasCode="true"
  tools:replace="android:hasCode">
  …
</application>

Note: Dynamic feature modules should not specify activities in their manifest withandroid:exported set totrue. That's because there's no guarantee that the devicehas downloaded the dynamic feature module when another app tries to launch theactivity. Additionally, your app should confirm that a dynamic feature isdownloaded before trying to access its code and resources. To learn more, readManage installed modules.

Test Dynamic Delivery

The best way to test Dynamic Delivery is through the Google Play Store. That'sbecause a lot of the benefits of Dynamic Delivery rely on deferring optimizedAPK generation, signing, and serving to the Play Store. So, whether youinclude basic support for Dynamic Delivery by uploading an app bundle orconfigure custom delivery options, you should use the following methods to testyour app with Dynamic Delivery"

• Share your app with a URL.This is the fastest way to upload your app bundle and share your app as aGoogle Play Store link with trusted testers. Additionally, this is the fastestway to test custom delivery options, such as downloading features on demand.
• Set up an open, closed, or internal test.This method provides structured test channels and is a good way to test thefinal release version of your app before you roll it out to external users.

Considerations for dynamic features

If you want to publish an app that includes dynamic feature modules to aproduction track, keep the following considerations in mind:

• Only devices running Android 5.0 (API level 21) and higher supportdownloading and installing dynamic features on demand. To make your dynamicfeature available to earlier versions of Android, make sure to enableFusing when you create a dynamic feature module.
• Make sure youenable SplitCompat,so that your app has immediate access to downloaded dynamic feature modules.
• If the download size for your dynamic feature is large, your app needs toobtain user confirmationbefore it can download the dynamic feature module to a device.
• Dynamic feature modules should not specify activities in their manifest withandroid:exported set totrue. That's because there's no guarantee that the devicehas downloaded the dynamic feature module when another app tries to launch theactivity. Additionally, your app should confirm that a dynamic feature isdownloaded before trying to access its code and resources. To learn more, readManage installed modules.
• Because dynamic delivery requires you to publish your app using an app bundle,make sure that you're aware of app bundleknown issues.

Additional resources

To learn more about using supporting Dynamic Delivery, try the followingresource.

Samples

• PlayCore API sample,a sample app that demonstrates usage of the PlayCore API to request anddownload dynamic features.

Blog posts

• What a new publishing format means for the future of Android
• Patchwork Plaid — A modularization story
• Google Santa Tracker — Moving to an Android App Bundle
• The latest Android App Bundle updates including the additional languages API

Videos

• Top 7 Takeaways for Android App Bundles

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