App size optimization in Android Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is app size optimization in Android development?

App size optimization means making your app smaller so it uses less storage on users' devices and downloads faster.

beginner

Name one common cause of large Android app size.

Including many large image files or unused libraries can make the app size bigger.

intermediate

What is the role of ProGuard or R8 in app size optimization?

They remove unused code and shrink the app, making it smaller and faster.

intermediate

How does resource shrinking help reduce app size?

Resource shrinking removes images, strings, and other files that your app does not use.

intermediate

What is Android App Bundle and how does it help with app size?

Android App Bundle lets Google Play deliver only the code and resources needed for a user’s device, reducing download size.

Which tool is used to remove unused code in Android apps?

A ProGuard

B Android Studio Layout Editor

C Firebase

D Gradle Wrapper

ProGuard (and R8) remove unused code to shrink app size.

What does resource shrinking do?

A Removes unused images and files

B Compresses APK files

C Optimizes network calls

D Increases app permissions

Resource shrinking removes unused resources like images and strings.

How does Android App Bundle reduce app size for users?

A By compressing all files into a zip

B By delivering only device-specific code and resources

C By removing all images

D By disabling animations

App Bundle lets Google Play send only what the device needs.

Which of these is NOT a good practice for app size optimization?

A Enabling code shrinking

B Using vector images instead of bitmaps

C Removing unused libraries

D Including all language translations even if unused

Including unused language files increases app size unnecessarily.

What is a benefit of smaller app size?

A More storage used

B More battery usage

C Faster downloads and installs

D Slower app startup

Smaller apps download and install faster, improving user experience.

Explain how code shrinking and resource shrinking work together to reduce Android app size.

Think about what parts of the app are removed to make it smaller.

Describe the benefits of using Android App Bundle for app size optimization.

Consider how Google Play customizes the app for each device.

Practice

1. What is the main purpose of enabling minifyEnabled in an Android app's build configuration?

easy

A. To add more debugging information

B. To increase the app's runtime speed

C. To remove unused code and reduce the app size

D. To enable multi-language support

Solution

1. Step 1: Understand minifyEnabled role

   This setting activates code shrinking tools like ProGuard or R8 to remove unused code.

2. Step 2: Effect on app size

   Removing unused code reduces the final APK or AAB size, making the app smaller.

3. Final Answer:

   To remove unused code and reduce the app size -> Option C

4. Quick Check:

   minifyEnabled = Remove unused code [OK]

Hint: minifyEnabled removes unused code to shrink app size [OK]

Common Mistakes:

• Thinking it improves runtime speed directly
• Confusing it with enabling debugging
• Assuming it adds features like language support

2. Which of the following is the correct way to enable resource shrinking in your build.gradle file for an Android app?

easy

A. shrinkResources = true

B. shrinkResources()

C. shrinkResources: true

D. shrinkResources true

Solution

1. Step 1: Check Gradle syntax for booleans

   In Gradle Groovy DSL, boolean properties are set with property true syntax.

2. Step 2: Apply to shrinkResources

   The correct syntax is shrinkResources true inside the buildTypes block.

3. Final Answer:

   shrinkResources true -> Option D

4. Quick Check:

   Gradle boolean syntax = property true [OK]

Hint: Use `property true` syntax in build.gradle (Groovy) [OK]

Common Mistakes:

• Using equals sign (Kotlin DSL)
• Using colon instead of space
• Calling it like a function

3. Given this build.gradle snippet, what will be the effect on the app size?

buildTypes {
  release {
    minifyEnabled true
    shrinkResources true
  }
}

medium

A. App size will increase due to added debugging info

B. App size will decrease by removing unused code and resources

C. App size will remain the same

D. App will fail to build due to syntax error

Solution

1. Step 1: Analyze minifyEnabled true

   This enables code shrinking tools to remove unused code.

2. Step 2: Analyze shrinkResources true

   This removes unused resources like images and strings from the APK.

3. Step 3: Combined effect on app size

   Both together reduce app size by removing unused code and resources.

4. Final Answer:

   App size will decrease by removing unused code and resources -> Option B

5. Quick Check:

   minifyEnabled + shrinkResources = smaller app [OK]

Hint: Both flags together shrink code and resources [OK]

Common Mistakes:

• Thinking it adds debugging info
• Assuming no effect on size
• Confusing syntax causing build failure

4. You enabled minifyEnabled true and shrinkResources true but your app crashes on startup. What is the most likely cause?

medium

A. You forgot to add ProGuard rules to keep necessary classes

B. You did not enable debugging mode

C. You used wrong syntax in build.gradle

D. You did not update your Android Studio version

Solution

1. Step 1: Understand minify effect on code

   Minify removes unused code but can mistakenly remove needed classes if rules are missing.

2. Step 2: Importance of ProGuard rules

   Proper rules keep essential classes from removal, preventing crashes.

3. Final Answer:

   You forgot to add ProGuard rules to keep necessary classes -> Option A

4. Quick Check:

   Missing ProGuard rules cause crashes after minify [OK]

Hint: Always add ProGuard rules when minifying [OK]

Common Mistakes:

• Blaming debugging mode
• Assuming syntax error without checking logs
• Ignoring ProGuard configuration

5. You want to reduce your Android app size by removing unused resources but keep some images used only in code via reflection. How should you configure your build to avoid removing these images?

hard

A. Add keep rules in proguard-rules.pro to keep resource references

B. Disable shrinkResources and rely only on minifyEnabled

C. Rename the images to start with underscore to protect them

D. Use shrinkResources with resConfigs to specify languages only

Solution

1. Step 1: Understand resource shrinking behavior

   Resource shrinking removes unused resources detected by static analysis.

2. Step 2: Handling resources used via reflection

   Resources accessed dynamically may appear unused and get removed unless explicitly kept.

3. Step 3: Use ProGuard keep rules

   Adding keep rules in proguard-rules.pro tells the shrinker to keep these resources.

4. Final Answer:

   Add keep rules in proguard-rules.pro to keep resource references -> Option A

5. Quick Check:

   Keep rules protect resources used dynamically [OK]

Hint: Use keep rules to protect resources used by reflection [OK]

Common Mistakes:

• Disabling shrinkResources loses size benefits
• Renaming files does not protect them
• Using resConfigs only filters languages, not resources