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.