Proguarding the New Way

Proguarding your builds is relatively easy and should always be done. Although device storage and data plans nowadays are not as constrained as they used to be, that still doesn’t mean we should ‘abuse’ the users resources because we were too lazy to add a few lines of code to our project.

Believe it or not, there are two different ways to proguard a build. The old way and the secret way. Officially, the secret way doesn’t really exist (this is the only ‘official’ reference I can find, it’s been marked as ‘incubating’ for at least the last year or two), in the Android documentation on proguarding a project, the old way is still referenced.

I can’t remember how I came across this new set of APIs, but ever since then it’s what I’ve used and it hasn’t let me down.

Old way

This is the way you are probably used to seeing. (NOTE: consumerProguardFiles should only be used in library modules so that it can expose its rules to an app module. proguardFiles should only be used in an app module. Both do not need to be defined in the same config).

This will, minify (proguard) your build, strip out any unused resources and use the applied rule files to prevent any breakages.

buildTypes {
  release {
    minifyEnabled true
    shrinkResources true
    proguardFiles getDefaultProguardFiles('proguard-android-optimize.txt', proguard-rules.pro)
    consumerProguardFiles 'consumer-rules.pro'
  }
}

New (secret-ish) way

Introducing the ‘new’ (not really) postprocessing block. It basically does the same as the above, but in a more defined and scoped way. You also have access to a more fine grained config. (NOTE: In library modules, removeUnusedResources should always be set to false, you’ll get a warning if you set it to true, read the warning, it’ll explain) The proguardFiles line from the above has been split up into proguardFiles which is your app specific rules and an optimizeCode flag which if set to true will apply the proguard-android-optimize.txt rules as-well.

buildTypes {
  release {
    postprocessing {
      proguardFiles 'proguard-rules.pro'
      consumerProguardFiles 'consumer-rules.pro'
      removeUnusedResources = true
      removeUnusedCode = true
      optimizeCode = true
      obfuscate = true
    }
  }
}