The Extensions SDK is what makes features like Photo Picker possible on older Android versions.
Project Mainline is a way for Google to deliver updates to some critical system components through the Google Play Services framework and the Google Play Store. Each Mainline module is delivered as either an APK file, an APEX file, or an APK-in-APEX. When a Mainline module is being updated, the user sees a “Google Play System Update” (GPSU) notification on their device. Effectively, to deliver updates to critical components, Google has bypassed the need to wait for an OEM to roll out an update, choosing to do the task itself. The company has now released the first public version of the Extension SDK, and it’s delivered to devices via a system module.
The biggest utility of the extension SDK for developers is the ability to bring the new Photo Picker API to devices running Android 11 and newer, despite being a feature that launched with Android 13. Google also says that developers will be able to implement AdServices APIs to get ready for testing the Android Privacy Sandbox that’s expected to launch in beta later this year. It’s an example of how the Extension SDK can be used to backport features to older Android versions without requiring a full system update.
Developers can check what version of the Extension SDK is installed on a user’s device by querying the extension version at runtime in the same way they would check other device attributes, such as build version. The AdServices API has been added in Extension SDK version 4, but Photo Picker has been there since version 2.
In the case of developers who are using Android Studio Flamingo or newer, they will be able to automatically generate the correct version checks for APIs that have launched via the Extension SDK. It’s entirely optional, but may help developers implement new features as they become available.You can read more about SDK Extensions and the documentation on the Privacy Sandbox Beta and the photo picker.