What is the difference between AAB and APK in the context of Android app building?

AAB (Android App Bundle) is a new publishing format that includes all the compiled code and resources of the app but defers APK generation and signing to the upload stage in Google Play. Google Play then uses this bundle to generate and serve optimized APKs for specific devices, containing only the necessary resources (e.g., for a particular screen density or CPU architecture).

APK (Android Package Kit) is the traditional package format for Android. It contains all the app's code, resources, and manifest in a single compressed file. APKs are created at build time and can be installed directly on an Android device.

Key differences:

• Purpose: AAB for publishing on Google Play (or other stores), APK for distribution and direct installation.
• Size: APK often contains redundant resources, whereas AAB allows generating size-optimized APKs for specific devices.
• APK generation: In the case of AAB, APKs are generated by Google Play based on the bundle. For APK, it is generated at build time by the developer.
• Dynamic modules: AAB better supports dynamic feature modules (on-demand features).
• Resource splitting: AAB allows using App Bundle Splitting to deliver only the necessary resources.

Overall, AAB is the preferred format for publishing on Google Play as it provides better size optimization and greater flexibility in delivering features to users.