Proguard : Shrink, obfuscate, and optimize your app

Proguard : Shrink, obfuscate, and optimize your app

To make your app as small as possible, you should enable shrinking in your release build to remove unused code and resources. When enabling shrinking, you also benefit from obfuscation, which shortens the names of your app’s classes and members, and optimization, which applies more aggressive strategies to further reduce the size of your app. This page describes how R8 performs these compile-time tasks for your project and how you can customize them.

When you build you project using Android Gradle plugin 3.4.0 or higher, the plugin no longer uses ProGuard to perform compile-time code optimization. Instead, the plugin works with the R8 compiler to handle the following compile-time tasks:

• Code shrinking (or tree-shaking): detects and safely removes unused classes, fields, methods, and attributes from your app and its library dependencies (making it a valuable tool for working around the 64k reference limit). For example, if you use only a few APIs of a library dependency, shrinking can identify library code that your app is not using and remove only that code from your app. To learn more, go to the section about how to shrink your code.
• Resource shrinking: removes unused resources from your packaged app, including unused resources in your app’s library dependencies. It works in conjunction with code shrinking such that once unused code has been removed, any resources no longer referenced can be safely removed as well. To learn more, go to the section about how to shrink your resources.
• Obfuscation: shortens the name of classes and members, which results in reduced DEX file sizes. To learn more, go to the section about how to obfuscate your code.
• Optimization: inspects and rewrites your code to further reduce the size of your app’s DEX files. For example, if R8 detects that the else {} branch for a given if/else statement is never taken, R8 removes the code for the else {} branch. To learn more, go to the section about code optimization.

Enable shrinking, obfuscation, and optimization

When you use Android Studio 3.4 or Android Gradle plugin 3.4.0 and higher, R8 is the default compiler that converts your project’s Java bytecode into the DEX format that runs on the Android platform. However, when you create a new project using Android Studio, shrinking, obfuscation, and code optimization is not enabled by default. That’s because these compile-time optimizations increase the build time of your project and might introduce bugs if you do not sufficiently customize which code to keep.

So, it’s best to enable these compile-time tasks when building the final version of your app that you test prior to publishing. To enable shrinking, obfuscation, and optimization, include the following in your project-level build.gradle file.

android {
    buildTypes {
        release {
            // Enables code shrinking, obfuscation, and optimization for only
            // your project's release build type.
            minifyEnabled true

            // Enables resource shrinking, which is performed by the
            // Android Gradle plugin.
            shrinkResources true

            // Includes the default ProGuard rules files that are packaged with
            // the Android Gradle plugin. To learn more, go to the section about
            // R8 configuration files.
            proguardFiles getDefaultProguardFile(
                    'proguard-android-optimize.txt'),
                    'proguard-rules.pro'
        }
    }
    ..

}

Source :https://developer.android.com/studio/build/shrink-code

Adding “Don’t Warn” Rules

“Don’t warn” rules tell Android Studio to ignore warnings. This can be dangerous, but if you know for sure that you’re not using a part of the code, it can come in handy. They work by specifying the package name. * is a wildcard – it doesn’t include sub-packages, whereas ** includes sub-packages. The rules for ProGuard go into the proguard-rules.pro file.

Add the following to the end of the proguard-rules.pro file to ignore warnings for the org.slf4j package:

-dontwarn org.slf4j.**