Getting Started with ProGuard

Nov 28 2018 , Kotlin 1.2, Android 4.4, Android Studio 3 Kotlin 1.2, Android 4.4, Android Studio 3

In this Android tutorial, you’ll learn how to strip down your app size by making use of ProGuard – an app shrinking and obfuscation tool. By Kolin Stürt.

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Getting Started with ProGuard

30 mins

Adding Annotations

With the Annotations Support Library, you can add @Keep to methods and classes you want to preserve. This is a great feature because it acts like documentation. The ProGuard information sits above your method as opposed to being in a separate file. Adding @Keep on a class will preserve the entire class. Adding @Keep on a method or field will keep the name of the method or field as-is.

In the BN.kt file, add a @Keep annotation to the top of the GO object.

Build and run the app. You should now see the bubbles again. This time, if you analyze the APK, you’ll see the secret gradient numbers are not so obvious:

Obfuscated code
Even if you follow those methods to the GO companion object, the numbers that are apparently returned are not the real ones. You tricked em!
Obfuscated code

You’re becoming a pro at ProGuard!

Where To Go From Here

You survived a crash course on ProGuard. Download the final project using the Download Materials button at the top or bottom of this tutorial.

You looked at how ProGuard has problems with reflection. ProGuard also has issues when you call a method from JNI (Java Native Interface). If you’re working with JNI, check out solutions in the JNI training article.

An Android Library (AAR) is able to make use of a transparent method that retrieves published keep rules automatically. See consumerProguardFiles on how to take advantage of this.

The makers of ProGuard, GuardSquare, have a commercial solution called DexGuard. It offers more protection than obfuscation. DexGuard encrypts the classes and strings as well as assets and resource files. It also provides app and device integrity checking which is important for keeping spammers out of your app.

While Android Studio comes with ProGuard built in, Google has been developing R8, which aims to be a drop-in replacement. It’s a new code shrinking and obfuscation tool that could replace ProGuard in the future. Check out Google’s R8 page for more information.

If you have any questions or comments, please join the discussion below!