App size optimization in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding App Size Reduction Techniques

Which of the following techniques directly reduces the APK size by removing unused code and resources?

A Using ProGuard or R8 to shrink and obfuscate the code

B Increasing the minSdkVersion to support fewer devices

C Adding more drawable resources for different screen density

D Using multiDex to split the app into multiple dex files

💡 Hint

Think about tools that remove unused parts of your code and resources.

ProGuard and R8 analyze your code and resources to remove unused parts, which reduces APK size. Increasing minSdkVersion or adding more resources can increase size. MultiDex helps with method limits but does not reduce size.

❓ ui_behavior

intermediate

Effect of Using Vector Drawables

You replace all PNG images with vector drawables in your Android app. What is the most likely effect on the app size and UI?

A App size stays the same but images lose quality on large screens

B App size increases because vector drawables are larger than PNGs

C App size decreases and images scale smoothly on all screen sizes

D App crashes because vector drawables are not supported on any Android version

💡 Hint

Think about how vector images work compared to bitmaps.

Vector drawables use XML to describe images, which usually reduces app size and scales smoothly on different screen sizes. They are supported on Android 5.0+ and via support libraries on older versions.

❓ lifecycle

advanced

Impact of Resource Qualifiers on APK Size

Your app includes multiple resource folders for different screen densities (mdpi, hdpi, xhdpi, xxhdpi). What happens to the APK size and resource loading when you build a universal APK?

A APK size increases but device loads all density resources at runtime

B APK size decreases because only the device's density resources are included automatically

C APK size stays the same but app crashes if device density resource is missing

D APK size increases because all density resources are included; device loads only matching density at runtime

💡 Hint

Consider what happens when you bundle resources for all devices in one APK.

A universal APK includes all resources for all densities, increasing APK size. At runtime, the device loads only the matching density resources, ignoring others.

❓ navigation

advanced

Using Dynamic Feature Modules to Optimize App Size

You want to reduce initial download size by delivering some features only when needed. Which Android feature allows this behavior?

A MultiDex to split code into multiple dex files

B Dynamic Feature Modules with Play Feature Delivery

C Using ProGuard to shrink code

D Adding all features in the base APK for faster access

💡 Hint

Think about modularizing features and downloading them on demand.

Dynamic Feature Modules let you separate features into modules that users download only when needed, reducing initial APK size. MultiDex and ProGuard help with code but not on-demand delivery.

📝 Syntax

expert

Analyzing Kotlin Code for Unused Resource Removal

Given this Kotlin snippet in an Android app, what is the value of unusedResourcesCount after running?

val resources = listOf("icon.png", "background.jpg", "unused.png")
val usedResources = listOf("icon.png", "background.jpg")
val unusedResourcesCount = resources.count { it !in usedResources }

A 1

B 2

C 0

D Throws a runtime exception

💡 Hint

Count how many items in resources are not in usedResources.

Only "unused.png" is not in usedResources, so the count is 1.

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