“minifyEnabled” vs “shrinkResources” - what's

Question

Background

According to the "Resource Shrinking" webpage of Andriod documentations (here), you can minimize the app's size via the build.gradle file, by using these lines:

android {
    ...

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

And, they say that when using it, it will also tell you how much is saved in the process:

When you enable shrinkResources, building your app should display output like the following during the build:

... Removed unused resources: Binary resource data reduced from 2570KB to 1711KB: Removed 33%

The questions

I can't find out the answers to those questions:

1. When using Android-Studio itself to create the signed app, where can I find the information of how much was saved and which files were removed/modified?
2. What exactly does "shrinkResources" do that "minifyEnabled" don't? And why do "shrinkResources" depend on "minifyEnabled" ?
3. Do any of those options affect the size and/or quality of image files?
4. Isn't Proguard responsible of shrinking source code? I ask this because it says "you have to enable minifyEnabled in order to turn on code shrinking,"

Answer 1

• shrinkResources is useful to reduce the dimension of your generated APK, stripping out any unused resource.
• minifiedEnabled simply runs Proguard which helps android plugin to package the APK without unused code, in order to shrink it

Answer 2

Let's see

When using Android-Studio itself to create the signed app, where can I find the information of how much was saved and which files were removed/modified?

Those are gonna be in the gradle log. Inside Android studio I believe those are shown in the Messages window (next to Android, Run, TODO windows).

What exactly does "shrinkResources" do that "minifyEnabled" don't? And why do "shrinkResources" depend on "minifyEnabled" ?

minify runs ProGuard. shrink remove resources that ProGuard flagged as unused.

Do any of those options affect the size and/or quality of image files?

No!

Isn't Proguard responsible of shrinking source code? I ask this because it says "you have to enable minifyEnabled in order to turn on code shrinking,"

ProGuard shrinks CODE ONLY; shrinkResources it's just the stuff from the /res/ folder. shrinkResources depends on the log output from ProGuard to run. ProGuard is the one who actually analyses the code to know what is unused.

edit:

I've just found a very nice blog post. CommonsWare posted it on some other stackOverlow question: http://cyrilmottier.com/2014/08/26/putting-your-apks-on-diet/

it explains it perfectly your follow up question:

why would one depend on the other?

from the post:

Proguard works on the Java side. Unfortunately, it doesn’t work on the resources side. As a consequence, if an image my_image in res/drawable is not used, Proguard only strips it’s reference in the R class but keeps the associated image in place.

that means, that shrinkResources only compares if a drawable is in the folder but not on the R class.

Answer 3

The answers to the questions 2 and 4 can be found in this video from Android Dev Summit 2015 along with some other useful information on this topic.

An overview of the points discussed were:

• shrinkResources is taken into account only if minifyEnabled is true

• minifyEnabled shrinks code, while shrinkResources shrinks resources that are not referenced from the code

• By default shrinkResources runs in safe mode. If you switch it to strict you can provide tools:keep and tools:discard flags manually to influence the resource shrinking.