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tree: aba8fc10cb1fe7b62292f4ad9d86e007dae0fe6a
  1. java/
  2. .bazelrc
  3. .gitignore
  4. BUILD
  5. MODULE.bazel
  6. proguard-android-optimize.txt
  7. proguard-rules.pro
  8. README.md
  9. WORKSPACE.bzlmod
examples/r8-optimized/README.md

R8 Optimized Android App Example

This example demonstrates how to build and optimize a simple Android application using R8.

What is R8 and Why Use It?

R8 is the code shrinker, optimizer, and dexer for Android developed by Google. In a single step, R8 handles:

  • Code Shrinking (Tree Shaking): Detects and safely removes unused classes, methods, fields, and attributes from your application and third-party dependencies.
  • Code Optimization: Inspects and rewrites code to improve runtime performance, inline methods, remove dead branches, and eliminate unused arguments.
  • Name Obfuscation: Renames types and members with short names to minimize DEX size.
  • Resource Shrinking: When paired with shrink_resources = True, removes unused Android resources that are no longer referenced after code shrinking.
  • Dexing: Directly converts Java bytecode to optimized Android DEX format.

Using R8 significantly reduces APK/AAB download and install sizes and memory footprint, decreases app startup time, and keeps method counts within optimal limits.

For in-depth details on configuring ProGuard/R8 keep rules and optimization flags, see docs/r8-optimization.md.

Building the Targets

Ensure that the ANDROID_HOME environment variable is set to the path of your Android SDK:

export ANDROID_HOME=/path/to/android/sdk

1. Build the Optimized APK (android_binary)

To build the standalone optimized APK:

bazel build //:r8_app

Output: bazel-bin/r8_app.apk

2. Build the Optimized Android App Bundle (android_application)

To build the optimized Android App Bundle (AAB):

bazel build //:r8_app_bundle

Output: bazel-bin/r8_app_bundle_unsigned.aab

3. Fast Incremental Installation with Mobile-Install

To build and install the application directly onto a connected Android device or running emulator:

bazel mobile-install //:r8_app

Configuration Files

  • BUILD: Defines the android_binary (r8_app) and android_application (r8_app_bundle) targets with proguard_specs and shrink_resources = True.
  • proguard-rules.pro: App-specific keep rules for preserving entry points like MainActivity.
  • proguard-android-optimize.txt: Default Android optimization rules for R8.
  • .bazelrc: Flags and settings needed to build the app with rules_android.