ProGuard and R8 optimization in Android Kotlin - Build, Publish & Deploy

Build & Publish - ProGuard and R8 optimization

Performance Impact

Using ProGuard and R8 helps your Android app run faster and use less memory. They remove unused code and shrink your app, which means the app loads quicker and uses less battery. This helps keep your app smooth at 60 frames per second, especially on older devices.

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How to Optimize for 60fps Rendering

Enable R8 in your build to automatically shrink and optimize your code. Use minifyEnabled true in your build.gradle. Keep your ProGuard rules simple and only keep what you need. Avoid keeping large libraries if unused. Test your app after shrinking to catch any missing code that might cause crashes.

Impact on App Bundle Size and Startup Time

ProGuard and R8 reduce your app size by removing unused classes and methods. Smaller apps download faster and start quicker. This improves user experience and reduces data usage. A smaller app bundle also means faster installation and less storage used on the device.

iOS vs Android Differences

ProGuard and R8 are Android-specific tools. iOS apps use different tools like Bitcode and Swift compiler optimizations. Android requires code shrinking because apps often include many libraries. iOS apps are usually smaller by default but use different app thinning methods.

Store Review Guidelines and Requirements

Google Play requires apps to be signed and optimized for performance. Using R8 and ProGuard helps meet performance guidelines by reducing app size and improving speed. Make sure your app does not remove code needed for Google Play services or analytics, or it may fail review.

Self Check

Your app takes 5 seconds to load this screen. What's likely wrong?

• You might not have enabled R8 or ProGuard, so your app is too large and slow to start.
• Your ProGuard rules might be too strict, removing needed code causing crashes or delays.
• You could have unused libraries bloating your app size and slowing startup.

Key Result

Using ProGuard and R8 in Android Kotlin projects reduces app size and memory use, improving startup speed and smooth 60fps UI performance. Proper configuration ensures faster downloads and passes Google Play performance guidelines.

Practice

1. What is the main purpose of enabling minifyEnabled true in your Android app's release build?

easy

A. To automatically generate UI layouts

B. To increase the app's debug information for easier troubleshooting

C. To disable ProGuard and R8 optimizations

D. To shrink and optimize the app code by removing unused parts

Solution

1. Step 1: Understand the role of minifyEnabled

   Setting minifyEnabled true activates code shrinking and optimization tools like ProGuard and R8.

2. Step 2: Identify the effect on app code

   These tools remove unused code and optimize the remaining code to reduce app size and improve performance.

3. Final Answer:

   To shrink and optimize the app code by removing unused parts -> Option D

4. Quick Check:

   minifyEnabled true = shrink and optimize [OK]

Hint: minifyEnabled true means code shrinking is ON [OK]

Common Mistakes:

• Thinking it increases debug info instead of reducing code
• Confusing minifyEnabled with disabling optimizations
• Assuming it generates UI layouts automatically

2. Which of the following is the correct way to specify a ProGuard rules file in your build.gradle for release builds?

easy

A. proguardFiles 'proguard-rules.txt'

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

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

D. minifyEnabled false

Solution

1. Step 1: Recall the standard syntax for ProGuard files

   The correct syntax uses getDefaultProguardFile for the default file and then adds custom rules.

2. Step 2: Match the correct order and file names

   proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro' correctly calls getDefaultProguardFile('proguard-android-optimize.txt') and then adds 'proguard-rules.pro'.

3. Final Answer:

   proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro' -> Option C

4. Quick Check:

   Correct ProGuard file syntax = proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro' [OK]

Hint: Default file uses getDefaultProguardFile() [OK]

Common Mistakes:

• Swapping file names or forgetting getDefaultProguardFile()
• Setting minifyEnabled false disables ProGuard
• Using wrong file extensions like .txt instead of .pro

3. Given this ProGuard rule:

-keep class com.example.MyClass { *; }

What will happen to MyClass during code shrinking?

medium

A. It will be kept intact with all its members

B. It will be removed if unused

C. Only its public methods will be kept

D. It will be renamed but removed if unused

Solution

1. Step 1: Understand the -keep rule

   The -keep directive tells ProGuard to keep the specified class and its members without removing or renaming them.

2. Step 2: Analyze the rule syntax

   The rule -keep class com.example.MyClass { *; } means keep the entire class and all its members intact.

3. Final Answer:

   It will be kept intact with all its members -> Option A

4. Quick Check:

   -keep class = keep all members [OK]

Hint: -keep means keep class and members intact [OK]

Common Mistakes:

• Thinking -keep removes unused classes
• Assuming only public methods are kept
• Confusing renaming with removal

4. You enabled minifyEnabled true but your app crashes at runtime due to missing classes. What is the most likely cause?

medium

A. You set minifyEnabled false by mistake

B. You forgot to add -keep rules for classes used via reflection

C. You used the wrong ProGuard file name in build.gradle

D. You disabled R8 in your project

Solution

1. Step 1: Identify the cause of missing classes

   When code shrinking removes classes used only by reflection, runtime crashes occur.

2. Step 2: Understand the role of -keep rules

   Adding -keep rules for such classes prevents their removal during shrinking.

3. Final Answer:

   You forgot to add -keep rules for classes used via reflection -> Option B

4. Quick Check:

   Missing classes after shrinking = missing -keep rules [OK]

Hint: Add -keep rules for reflection-used classes [OK]

Common Mistakes:

• Assuming minifyEnabled false causes missing classes
• Confusing file name errors with missing classes
• Thinking disabling R8 causes missing classes

5. You want to keep all classes in the package com.example.models but allow R8 to rename their members to reduce size. Which ProGuard rule should you use?

hard

A. -keepnames class com.example.models.**

B. -keepclassmembers class com.example.models.** { *; }

C. -keep class com.example.models.** { *; }

D. -keepclassmembernames class com.example.models.** { *; }

Solution

1. Step 1: Understand the difference between -keep and -keepnames

   -keep prevents removal and renaming; -keepnames prevents renaming but allows removal.

2. Step 2: Match the requirement

   You want to keep classes but allow member renaming, so -keepnames on classes is correct.

3. Final Answer:

   -keepnames class com.example.models.** -> Option A

4. Quick Check:

   Keep classes but rename members = -keepnames [OK]

Hint: -keepnames keeps class names but allows member renaming [OK]

Common Mistakes:

• Using -keep which prevents renaming
• Confusing -keepclassmembers with -keepnames
• Assuming -keepclassmembernames keeps classes