Android Asset Packaging Tool 2.0 (AAPT2) release notes

Version 2.9

Added sparse resource type encoding, which encodes resource entries that are sparse with a binary search tree representation. Only available when minSdkVersion >= API O or resource qualifier of resource types is >= v26 (or whatever API level O becomes). Enabled with --enable-sparse-encoding flag.

Adds an optimization pass that supports:
- stripping out any density assets that do not match the --target-densities list of densities.
- resource deduping when the resources are dominated and identical (already happens during link phase but this covers apps built with aapt).
- new sparse resource type encoding with the --enable-sparse-encoding flag if possible (minSdkVersion >= O or resource qualifier >= v26).

Adds shared library support. Build a shared library with the --shared-lib flag. Build a client of a shared library by simply including it via -I.

Fixes bug where psuedolocalization auto-translated strings marked 'translateable="false"'.

Transition XML versioning: Adds a new flag --no-version-transitions to disable automatic versioning of Transition XML resources.

Duplicate resource filtering: removes duplicate resources in dominated configurations that are always identical when selected at runtime. This can be disabled with --no-resource-deduping.

Configuration Split APK support: supports splitting resources that match a set of configurations to a separate APK which can be loaded alongside the base APK on API 21+ devices. This is done using the flag --split path/to/split.apk:<config1>[,<config2>,...].
SDK version resource filtering: Resources with an SDK version qualifier that is unreachable at runtime due to the minimum SDK level declared by the AndroidManifest.xml are stripped.

Pseudo-localization: generates pseudolocalized versions of default strings when the --pseudo-localize option is specified.
Legacy mode: treats some class of errors as warnings in order to be more compatible with AAPT when --legacy is specified.
Compile directory: treats the input file as a directory when --dir is specified. This will emit a zip of compiled files, one for each file in the directory. The directory must follow the Android resource directory structure (res/values-[qualifiers]/file.ext).

Automatic attribute versioning: adds version qualifiers to resources that use attributes introduced in a later SDK level. This can be disabled with --no-auto-version.
Min SDK resource filtering: removes resources that can't possibly be selected at runtime due to the application's minimum supported SDK level.