Recently when I enabled Proguard in my program like the following:

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

I faced the problem that it tooks like for ever for the process of transformClassesAndResourcesWithProguardForRelease. This problem happens when you have multiple libraries need to be Proguard/Dexguard. Add the line multiDexEnabled true in to your gradle defaultConfig will fix this problem.

How to apply Proguard/Dexguard

Proguard/Dexguard shrink and obsfucate resources and codes by scanning and looping up the dependencies. It will do everything it thinks necessary. To apply proguard, simple change minifyEnabled in the module/app you want to apply to be true. Android will apply for Proguard automatically.

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buildTypes {
    release {
        minifyEnabled true
    }
}

Based on the article I wrote: Decode Android Project from APK, we know that revise engineers can easily decode codes and get your source files. there are a number of possible vulnerabilities for unprotected mobile applications, such as insertion of malware, intellectual property theft, priacy and data theft. Therefore, we can use ProGuard or DexGuard to protect. This is a way to apply multiple obfuscation and encryption to make our source codes unreadable.

If an Android App not doing encryption or obfuscation, an APK (Android application package) is easily be decoded. A reverse engineer can see its source codes and XML files.

Here is the procedure how to decoding .apk files to get source files.

1. Go to project, Build -> Build APK(s). After .apk file is generated, click “locate” to the path of the file.
2. Create a new folder, let’s call it “decode”.