App size optimization in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to enable ProGuard for app size optimization in the build.gradle file.

Android Kotlin

android {
    buildTypes {
        release {
            minifyEnabled = [1]
        }
    }
}

Drag options to blanks, or click blank then click option'

A"true"

Bfalse

Ctrue

D"false"

Attempts:

3 left

💡 Hint

Common Mistakes

Using string values like "true" instead of boolean true.

Setting minifyEnabled to false disables code shrinking.

Setting minifyEnabled to true enables code shrinking and obfuscation, which helps reduce app size.

2fill in blank

medium

Complete the code to exclude unused resources during build to reduce app size.

Android Kotlin

android {
    buildTypes {
        release {
            shrinkResources = [1]
        }
    }
}

Drag options to blanks, or click blank then click option'

Atrue

Bfalse

C"false"

D"true"

Attempts:

3 left

💡 Hint

Common Mistakes

Using string values instead of boolean.

Setting shrinkResources to false disables resource shrinking.

Setting shrinkResources to true removes unused resources, helping to reduce app size.

3fill in blank

hard

Fix the error in the Kotlin code to load only necessary native libraries to reduce app size.

Android Kotlin

System.loadLibrary([1])

Drag options to blanks, or click blank then click option'

A"native-lib"

Blibnative

C"libnative"

Dnative-lib

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the library name without quotes causes a compile error.

Including the lib prefix or file extension is incorrect.

The System.loadLibrary function requires the library name as a string with quotes, without the lib prefix or file extension.

4fill in blank

hard

Fill both blanks to configure ABI splits to reduce APK size by targeting specific CPU architectures.

Android Kotlin

android {
    splits {
        abi {
            enable = [1]
            reset()
            include [2]
        }
    }
}

Drag options to blanks, or click blank then click option'

Atrue

Bfalse

C["armeabi-v7a", "arm64-v8a"]

D["x86", "mips"]

Attempts:

3 left

💡 Hint

Common Mistakes

Setting enable to false disables ABI splits.

Including uncommon or unsupported ABIs.

Enabling ABI splits with true and including common architectures like armeabi-v7a and arm64-v8a helps reduce APK size by building only for those CPUs.

5fill in blank

hard

Fill all three blanks to create a ProGuard rule that keeps only the necessary classes and removes unused code.

Android Kotlin

-keep class [1] {
    [2];
}
-dontwarn [3]

Drag options to blanks, or click blank then click option'

Acom.example.app.MainActivity

Bpublic *

Ccom.example.app.**

Dandroid.support.**

Attempts:

3 left

💡 Hint

Common Mistakes

Using wildcard for class name instead of specific class.

Not specifying members to keep.

Ignoring warnings from support libraries.

This ProGuard rule keeps the MainActivity class and all its public members, and suppresses warnings for the Android support library to avoid build errors.

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