The document discusses effective techniques for optimizing ProGuard configuration rules to reduce APK size. It outlines steps like removing duplicated and redundant rules, and using "-whyareyoukeeping" to analyze rules. This helps refine the configuration by only keeping necessary rules. The result was a 5.52% smaller APK size and 11.3% fewer methods. Care must be taken with libraries using reflection or dynamic naming. R8 is now the default compiler which handles ProGuard configs differently.

1. Ansgar Lin - Android team of Oath: Yahoo TW
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如何有效精簡ProGuard規則以達到
縮⼩小apk之⽬目的

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3. Effective ProGuard keep rules for smaller applications
(Google I/O ’18)
• https://www.youtube.com/watch?v=x9T5EYE-QWQ
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About the topic

4. • A most popular open source tool in the Android world.
• Shrink apk by removing unused code at run-time.
• Obfuscate code to provide minimal protections against reverse
engineering
• Add “-keep class * extends ClassA” into ProGuard configuration,
you can tell ProGuard don’t touch any subclass of ClassA
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What is ProGuard?
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What is ProGuard?
// In build.gradle
android {
buildTypes {
debug {
minifyEnabled true
proguardFiles getDefaultProguardFile('proguard-android.txt'),
'proguard-project.txt'
}
}
}

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What is ProGuard?
• A most popular open source tool in the Android world.
• Shrink apk by removing unused code at run-time.
• Obfuscate code to provide minimal protections against reverse
engineering
• Add “-keep class * extends ClassA” into ProGuard configuration,
you can tell ProGuard don’t touch any subclass of ClassA

7. 7
What is ProGuard?
// In build.gradle
android {
buildTypes {
debug {
minifyEnabled true
proguardFiles getDefaultProguardFile('proguard-android.txt'),
'proguard-project.txt'
}
}
}

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What is ProGuard?

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Following outline
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• Refinement steps & reasons
• Result
• Trouble shoot
• Q & A

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Step 1:
Remove duplicated rules

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ProGuard Work Flow - Read Configuration
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ProGuard Work Flow - Read Configuration
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ProGuard Work Flow - Read Configuration
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ProGuard Work Flow - Read Configuration
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ProGuard Work Flow - Read Configuration
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ProGuard Work Flow - Read Configuration
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ProGuard Work Flow - Read Configuration
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Refine ProGuard Configuration
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ProGuard Work Flow - Read Configuration
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proguard-android、proguard-default和proguard-android-optimize

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Refine ProGuard Configuration

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Step 2:
Remove redundant rules

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ProGuard Work Flow - Read Input
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ProGuard Work Flow - Read Input
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ProGuard Work Flow - Read Input
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ProGuard Work Flow - Read Input
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Won’t get ProGuard
= “-keep” on everything

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Refine ProGuard Configuration

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Step 3:
Use “-whyareyoukeeping”

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• “-keep class com.example.Blur”
—> “-whyareyoukeeping class com.example.Blur”
Refine ProGuard Configuration
com.example.Blur
is invoked by com.example.BlurView: doWorkA(int)
is invoked by com.example.BlurView: BlurView(android.content.Context)
is invoked by com.example.SelectActivity: onCreate(android.os.Bundle)
implements android.app.Activity: onCreate(android.os.Bundle)
is a library method.

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Foot note
• “-keep class com.example.Blur”
—> “-whyareyoukeeping class com.example.Blur”
Refine ProGuard Configuration
com.example.Blur
is invoked by com.example.BlurView: doWorkA(int)
is invoked by com.example.BlurView: BlurView(android.content.Context)
is invoked by com.example.SelectActivity: onCreate(android.os.Bundle)
implements android.app.Activity: onCreate(android.os.Bundle)
is a library method.

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Foot note
• “-keep class com.example.Blur”
—> “-whyareyoukeeping class com.example.Blur”
Refine ProGuard Configuration
com.example.Blur
is invoked by com.example.BlurView: doWorkA(int)
is invoked by com.example.BlurView: BlurView(android.content.Context)
is invoked by com.example.SelectActivity: onCreate(android.os.Bundle)
implements android.app.Activity: onCreate(android.os.Bundle)
is a library method.

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Foot note
• “-keep class com.example.Blur”
—> “-whyareyoukeeping class com.example.Blur”
Refine ProGuard Configuration
com.example.Blur
is invoked by com.example.BlurView: doWorkA(int)
is invoked by com.example.BlurView: BlurView(android.content.Context)
is invoked by com.example.SelectActivity: onCreate(android.os.Bundle)
implements android.app.Activity: onCreate(android.os.Bundle)
is a library method.

32. • “-keep class com.example.Blur”
—> “-whyareyoukeeping class com.example.Blur”
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Foot note
Refine ProGuard Configuration
com.example.Blur
is invoked by com.example.BlurView: doWorkA(int)
is invoked by com.example.BlurView: BlurView(android.content.Context)
is invoked by com.example.SelectActivity: onCreate(android.os.Bundle)
implements android.app.Activity: onCreate(android.os.Bundle)
is a library method.

33. • “-keep class com.example.Blur”
—> “-whyareyoukeeping class com.example.Blur”
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Foot note
Refine ProGuard Configuration
com.example.Blur
is invoked by com.example.BlurView: doWorkA(int)
is invoked by com.example.BlurView: BlurView(android.content.Context)
is invoked by com.example.SelectActivity: onCreate(android.os.Bundle)
implements android.app.Activity: onCreate(android.os.Bundle)
is a library method.

34. • “-keep class com.example.Blur”
—> “-whyareyoukeeping class com.example.Blur”
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Foot note
Refine ProGuard Configuration
com.example.Blur
is invoked by com.example.BlurView: doWorkA(int)
is invoked by com.example.BlurView: BlurView(android.content.Context)
is invoked by com.example.SelectActivity: onCreate(android.os.Bundle)
implements android.app.Activity: onCreate(android.os.Bundle)
is a library method.

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Foot note
• message from `-whyareyoukeeping`
• is a library class/method/field.
• is not been kept
• nothing
• is kept by a directive in the configuration.
Refine ProGuard Configuration

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Foot note
• message from `-whyareyoukeeping`
• is a library class/method/field.
• is not been kept
• nothing
• is kept by a directive in the configuration.
-keep class com.example.Blur
-whyareyoukeeping class com.example.Blur
Refine ProGuard Configuration

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The Result

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購物中⼼心 - APK size (M)
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0.9
5.52%

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購物中⼼心 - Method count
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12932
11.30%

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購物中⼼心 - Method count (com.yahoo.*)
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2294

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購物中⼼心 - Method count (com.google.*)
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9407

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Recap

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1. Remove duplicated rules
Refine ProGuard Configuration

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2. Remove redundant rules
Refine ProGuard Configuration

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Foot note
3. Use “-whyareyoukeeping”
• “-keep class com.example.Blur”
—> “-whyareyoukeeping class com.example.Blur”
Refine ProGuard Configuration

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Trouble shoot

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What should be careful?
Foot note
• 3-rd Library implements with reflection.
• Glide: initialization
• Parsing data with field names
• Gson + Retrofit: JSON model
• Anything implementation with static name.

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What should be careful?
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• 3-rd Library implements with reflection.
• Glide: initialization
• Parsing data with field names
• Gson + Retrofit: JSON model
• Anything implementation with static name.

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W/ProGuard: The class 'com.example.SampleActivity' is calling Class.forName to retrieve
the class 'com.exmaple.NoneExistClass', but the latter could not be found.
It may have been obfuscated or shrunk.
You should consider preserving the class with its original name,
with a setting like:
-keep class com.exmaple.NoneExistClass
W/System.err: java.lang.ClassNotFoundException: com.exmaple.NoneExistClass
at java.lang.Class.classForName(Native Method)
• Add “-addconfigurationdebugging”
What should be careful?

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W/ProGuard: The class 'com.example.SampleActivity' is calling Class.forName to retrieve
the class 'com.exmaple.NoneExistClass', but the latter could not be found.
It may have been obfuscated or shrunk.
You should consider preserving the class with its original name,
with a setting like:
-keep class com.exmaple.NoneExistClass
W/System.err: java.lang.ClassNotFoundException: com.exmaple.NoneExistClass
at java.lang.Class.classForName(Native Method)
• Add “-addconfigurationdebugging”
What should be careful?

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W/ProGuard: The class 'com.example.SampleActivity' is calling Class.forName to retrieve
the class 'com.exmaple.NoneExistClass', but the latter could not be found.
It may have been obfuscated or shrunk.
You should consider preserving the class with its original name,
with a setting like:
-keep class com.exmaple.NoneExistClass
W/System.err: java.lang.ClassNotFoundException: com.exmaple.NoneExistClass
at java.lang.Class.classForName(Native Method)
• Add “-addconfigurationdebugging”
Only use in debug version
What should be careful?

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• ClassNotFoundException
• NoSuchFieldException
• NoSuchMethodException
• RuntimeException
• UnsatisfiedLinkError
• IOException
• Add “-addconfigurationdebugging”
What should be careful?

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Foot note
W/ProGuard: The class 'com.example.SampleActivity' is calling Class.forName to retrieve
the class 'com.exmaple.NoneExistClass', but the latter could not be found.
It may have been obfuscated or shrunk.
You should consider preserving the class with its original name,
with a setting like:
-keep class com.exmaple.NoneExistClass
W/System.err: java.lang.ClassNotFoundException: com.exmaple.NoneExistClass
at java.lang.Class.classForName(Native Method)
• Add “-addconfigurationdebugging”
What should be careful?

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R8

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R8
Foot note
• Powered by Google
• Default enable after Android Studio(3.3)
• Java bytecode(.class) —> Dalvik bytecode(.dex)
• ProGuard configuration is acceptable.
• Changes:
• “-addconfigurationdebugging” will be ignored by default.
• Error detection while compiling.

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Your turn!
Foot note
• Start playing with ProGuard

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Q & A

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Reference
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• MCE 2014 - Eric Lafortune - ProGuard, Optimizer and
Obfuscator in the Android SDK
• Effective ProGuard keep rules for smaller applications
(Google I/O ’18)
• About ProGuard - Part 1