ProGuard and R8 optimization in Android Kotlin

Introduction

ProGuard and R8 help make your Android app smaller and faster by removing unused code and optimizing what remains.

When you want to reduce the size of your app before publishing it.

When you want to protect your app code from easy copying or reverse engineering.

When you want to improve app performance by removing unnecessary parts.

When you want to shrink and optimize your app automatically during build.

When you want to keep your app secure and efficient for users.

Syntax

Android Kotlin

android {
    buildTypes {
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

minifyEnabled true turns on code shrinking and optimization.

proguardFiles lists the configuration files for rules to keep or remove code.

Examples

Disables code shrinking and optimization, useful for debugging.

Android Kotlin

minifyEnabled false

Enables shrinking with custom ProGuard rules file.

Android Kotlin

minifyEnabled true
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'my-proguard-rules.pro'

Typical setup for release build with R8 optimization and ProGuard rules.

Android Kotlin

buildTypes {
    release {
        minifyEnabled true
        proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
    }
}

Sample App

This example shows a simple Android app with ProGuard and R8 enabled for release builds. The ProGuard rules keep the main activity so it is not removed. When you build the release version, unused code is removed and the app size is smaller.

Android Kotlin

plugins {
    id 'com.android.application'
    id 'org.jetbrains.kotlin.android'
}

android {
    namespace 'com.example.proguarddemo'
    compileSdk 33

    defaultConfig {
        applicationId 'com.example.proguarddemo'
        minSdk 21
        targetSdk 33
        versionCode 1
        versionName '1.0'
    }

    buildTypes {
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

// proguard-rules.pro
# Keep MainActivity class
-keep class com.example.proguarddemo.MainActivity { *; }

// MainActivity.kt
package com.example.proguarddemo

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import android.widget.TextView

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val textView = TextView(this)
        textView.text = "Hello ProGuard and R8!"
        setContentView(textView)
    }
}

Important Notes

R8 is the default code shrinker and optimizer in Android Studio now, replacing ProGuard but still using ProGuard rules.

Always test your app after enabling minify to make sure important code is not removed.

You can add custom rules in proguard-rules.pro to keep code needed by reflection or libraries.

Summary

ProGuard and R8 help shrink and optimize your Android app code.

Enable minifyEnabled true in release build to activate them.

Use ProGuard rules files to control what code to keep or remove.