How to minify a Flutter app with Proguard?

Question

I already made a Flutter app. The release apk is about 14MB. I searched methods to minify this and found this ons: https://flutter.io/android-release/#enabling-proguard

But my question is, how can I get to know all my used additional libraries for step 1? Are there any commands to know them or is it just all the dependencies that I added to the pubspec.yaml ?

How do I need to implement them in this file /android/app/proguard-rules.pro?

Answer 1

First, we will enable shrinking and obfuscation in the build file. Find build.gradle file which sits inside /android/app/ folder and add lines in bold

android {

    ...

    buildTypes {

        release {

            signingConfig signingConfigs.debug     

            minifyEnabled true
            useProguard true

            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro' 

        }
    }
}

Next we will create a configuration which will preserve entire Flutter wrapper code. Create /android/app/proguard-rules.pro file and insert inside:

#Flutter Wrapper
-keep class io.flutter.app.** { *; }
-keep class io.flutter.plugin.**  { *; }
-keep class io.flutter.util.**  { *; }
-keep class io.flutter.view.**  { *; }
-keep class io.flutter.**  { *; }
-keep class io.flutter.plugins.**  { *; }

Answer 2

I will leave this answer here as an addition for any poor soul that has to deal with this issue and encounters this thread.

As of December 2021 with the latest Android Sdk, Studio and Flutter versions, if you try to douseProguard true it will not work because it's obsolete. Sadly, Gradle will not tell you this, instead, you will get an error like this:

A problem occurred evaluating project ':app'.

> No signature of method: build_7cqkbrda1q788z3b02yxbvrx9.android() is applicable for argument types: (build_7cqkbrda1q788z3b02yxbvrx9$_run_closure2) values: [build_7cqkbrda1q788z3b02yxbvrx9$_run_closure2@41108b15]

Which as you can see it is complete gibberish and not useful. The secret is to just not use useProguard at all. By default Flutter is setup to use R8 which handles minification now on Android.

Here is a so post about this for reference: Gradle : DSL element 'useProguard' is obsolete and will be removed soon