ProGuard — shrinking, optimization, obfuscation, and preverification of Java bytecode.

Proguard optimizes the bytecode, removes unused codes, and obfuscates the classes, fields, methods with shorter names. Optimization operates with java bytecode. Since android runs on Dalvik bytecode which is converted from java bytecode, some optimizations usually doesn’t work well ( So you should be careful ).

The obfuscated code makes your APK difficult to reverse engineer, which is the main reason why most of the developers choose proguard.

Proguard can sometimes break your code up since it renames almost everything. Be sure to thoroughly test your app before release, especially after changing proguard config.

Prevent Obfuscation In Some Classes

Every app has some kind of data classes, models, or some important classes which they cannot be obfuscated. In such circumstances, we cannot let proguard to rename or remove any fields of those classes. It’s a safe bet to add a @Keep annotation on the whole class or methods, or a wildcard rule on proguard-rules.pro.

1 – @Keep Annotation:

Denotes that the annotated element should not be renamed when the code is minified at build time. This is typically used on methods and classes that are accessed only via reflection so a compiler may think that the code is unused.

@Keep
  public void foo() {
      ...
  }
 

Note that: This annotation is available only when using the Annotations Support Library.

2 – Using ProGuard, keep class fields with wildcard:

-keepclassmembers class com.my.package.** {
    public protected <fields>;
    private *** string*;
}

Tips & Tricks in Proguard

• Proguard does not obfuscate the class names and public methods called in AndroidManifest.xml by default. So you don’t have to add ‘keep’in those classes.
• Android Analyser can help you a lot while deciding which rules to add in proguard. Yet, to prevent unexpected crashes, be sure to test your release app in depth at the end.
• To create released apk, change your directory in terminal then add the following snippet and run.

  ./gradlew assembleRelease

• Finally If you are building library and want to change your release lib name, add the following line to your build-gradle(module: app) in android {} part.

  project.archivesBaseName = "SomeExample";
  

  Some useful Q&As:

  https://stackoverflow.com/questions/35321742/android-proguard-most-aggressive-optimizations

  https://stackoverflow.com/questions/33958972/how-to-obfuscate-everything-but-public-method-names-and-attributes-with-proguard

  https://stackoverflow.com/questions/30526173/obfuscate-private-fields-using-proguard

  https://stackoverflow.com/questions/23365021/how-to-tell-proguard-to-keep-private-fields-without-specifying-each-field

  https://stackoverflow.com/questions/17040220/how-to-tell-proguard-to-obfuscate-method-and-class-names

  https://stackoverflow.com/questions/27948088/hiding-package-name-using-proguard-but-keeping-certain-methods-in-a-class-public?rq=1

  https://stackoverflow.com/questions/33958972/how-to-obfuscate-everything-but-public-method-names-and-attributes-with-proguard

  https://stackoverflow.com/questions/35321742/android-proguard-most-aggressive-optimizations

  PS: Great Documentation in Turkish: https://medium.com/android-t%C3%BCrkiye/android-proguard-kullan%C4%B1m%C4%B1-700affa6625c