Behavior changes: apps targeting API 29+

Android 10 includes updated system behavior changes that may affect your app. The changes listed in this document apply exclusively to apps that are targeting API 29 or higher. If your app sets targetSdkVersion to "29" or higher, you should modify your app to support these behaviors properly, where applicable.

Make sure to also review the list of behavior changes that affect all apps running on Android 10.

Updates to non-SDK interface restrictions

To help ensure app stability and compatibility, the platform started restricting which non-SDK interfaces your app can use in Android 9 (API level 28). Android 10 includes updated lists of restricted non-SDK interfaces based on collaboration with Android developers and the latest internal testing. Our goal is to make sure that public alternatives are available before we restrict non-SDK interfaces.

If you will not be targeting Android 10 (API level 29), some of these changes might not immediately affect you. However, while you can currently use non-SDK interfaces that are part of the greylist (depending on your app's target API level), using any non-SDK method or field always carries a high risk of breaking your app.

If you are unsure if your app uses non-SDK interfaces, you can test your app to find out. If your app relies on non-SDK interfaces, you should begin planning a migration to SDK alternatives. Nevertheless, we understand that some apps have valid use cases for using non-SDK interfaces. If you cannot find an alternative to using a non-SDK interface for a feature in your app, you should request a new public API.

To learn more, see Updates to non-SDK interface restrictions in Android 10 and see Restrictions on non-SDK interfaces.

Shared memory

Ashmem has changed the format of dalvik maps in /proc/<pid>/maps, affecting apps that directly parse the maps file. Application developers should test the /proc/<pid>/maps format on devices that run Android 10 or higher and parse accordingly if the app depends on dalvik map formats.

Apps targeting Android 10 cannot directly use ashmem (/dev/ashmem) and must instead access shared memory via the NDK’s ASharedMemory class. In addition, apps cannot make direct IOCTLs to existing ashmem file descriptors and must instead use either the NDK’s ASharedMemory class or the Android Java APIs for creating shared memory regions. This change increases security and robustness when working with shared memory, improving performance and security of Android overall.

Removed execute permission for app home directory

Untrusted apps that target Android 10 cannot invoke exec() on files within the app's home directory. This execution of files from the writable app home directory is a W^X violation. Apps should load only the binary code that's embedded within an app's APK file.

In addition, apps that target Android 10 cannot in-memory modify executable code from files which have been opened with dlopen(). This includes any shared object (.so) files with text relocations.

Android runtime only accepts system-generated OAT files

The Android runtime (ART) no longer invokes dex2oat from the application process. This change means that the ART will only accept OAT files that the system has generated.

Enforcing AOT correctness in ART

In the past, the ahead-of-time (AOT) compilation performed by the Android Runtime (ART) could cause runtime crashes if the classpath environment was not the same at compile time and runtime. Android 10 and higher always require these environment contexts to be the same, resulting in the following changes in behavior:

• Custom class loaders—that is, class loaders written by apps, unlike class loaders from the dalvik.system package—aren't AOT-compiled. This is because ART cannot know about customized class lookup implementation at runtime.
• Secondary dex files—that is, the dex files loaded manually by apps not in the primary APK—are AOT-compiled in the background. This is because first-use compilation might be too expensive, leading to unwanted latency before execution. Note that for apps, adopting splits and moving away from secondary dex files is recommended.
• Shared libraries in Android (the entries <library> and <uses-library> in an Android manifest) are implemented using a different class loader hierarchy than the one used in previous versions of the platform.

Permissions changes for fullscreen intents

Apps that target Android 10 or higher and use notifications with fullscreen intents must request the USE_FULL_SCREEN_INTENT permission in their app's manifest file. This is a normal permission, so the system automatically grants it to the requesting app.

If an app that targets Android 10 or higher attempts to create a notification with a fullscreen intent without requesting the necessary permission, the system ignores the fullscreen intent and outputs the following log message:

Package your-package-name: Use of fullScreenIntent requires the USE_FULL_SCREEN_INTENT permission

Support for foldables

Android 10 has changes that support foldables and large screen devices.

When an app runs on Android 10, the onResume() and onPause() methods work differently. When multiple apps appear at the same time in multi-window or multi-display mode, all the focusable top activities in visible stacks are in the resumed state, but only one of them, the "topmost resumed" activity, actually has focus. When running on versions earlier than Android 10, only a single activity in the system can be resumed at a time, all other visible activities are paused.

Do not confuse "focus" with the "topmost resumed" activity. The system assigns priorities to activities based on z-order to give higher priority to the activities that the user interacted with last. An activity can be top-resumed, but not have focus (for example, if the notification shade is expanded).

In Android 10 (API level 29) and later, you can subscribe to the onTopResumedActivityChanged() callback to be notified when your activity acquires or loses the topmost resumed position. This is the equivalent of the resumed state before Android 10 and can be useful as a hint if your app is using exclusive or singleton resources that might need to be shared with other apps.

The behavior of the resizeableActivity manifest attribute has also changed. If an app sets resizeableActivity=false in Android 10 (API level 29) or later, it might be put in compatibility mode when the available screen size changes, or if the app moves from one screen to another.

Apps can use the android:minAspectRatio attribute, introduced in Android 10, to indicate the screen ratios that your app supports.

Starting with version 3.5, Android Studio's emulator tool includes 7.3" and 8" virtual devices for testing your code with larger screens.

For more information, see Building apps for Foldables.

java.io.FileChannel.map() changes

Starting in Android 10, FileChannel.map() isn't supported for non-standard files, like /dev/zero, whose size cannot be changed using truncate(). Previous versions of Android swallowed the errno returned by truncate(), but Android 10 throws an IOException. If you need the old behavior, you must use native code.