Android build configuration in Flutter - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

Understanding Android build flavors in Flutter

You have two build flavors: dev and prod. Which command builds the dev flavor APK?

A flutter build apk --flavor prod

B flutter build apk --flavor dev

C flutter run --flavor prod

D flutter run --flavor dev

💡 Hint

Use the build command with the flavor name to create the APK.

The command 'flutter build apk --flavor dev' builds the APK for the dev flavor. 'flutter run' runs the app on a device but does not create a build artifact.

🧠 Conceptual

intermediate

Purpose of build.gradle in Android Flutter projects

What is the main role of the build.gradle file inside the Android folder of a Flutter project?

A It defines Android build settings like SDK versions, dependencies, and signing configs.

B It contains Flutter Dart code for UI components.

C It manages iOS build configurations.

D It stores Flutter package dependencies.

💡 Hint

Think about what controls Android-specific build details.

The build.gradle file configures Android build parameters such as SDK versions, dependencies, and signing. Flutter Dart code and package dependencies are managed elsewhere.

📝 Syntax

advanced

Correct syntax for signing config in build.gradle

Which option correctly defines a signing config named release in the Android build.gradle file?

A

signingConfigs {
    release {
        storeFile = file('keystore.jks')
        storePassword = 'password'
        keyAlias = 'key'
        keyPassword = 'password'
    }
}

B

signingConfigs {
    release: {
        storeFile = 'keystore.jks'
        storePassword = 'password'
        keyAlias = 'key'
        keyPassword = 'password'
    }
}

C

signingConfigs {
    release {
        storeFile 'keystore.jks'
        storePassword 'password'
        keyAlias 'key'
        keyPassword 'password'
    }
}

D

signingConfigs {
    release {
        storeFile file('keystore.jks')
        storePassword 'password'
        keyAlias 'key'
        keyPassword 'password'
    }
}

💡 Hint

In Gradle Groovy DSL (used in Flutter), properties in signingConfigs blocks use no '=' and file() for paths.

Option D uses correct Gradle Groovy syntax (standard in Flutter android/app/build.gradle): storeFile file('keystore.jks') with no '='. Option D uses invalid ':', C uses '=' (for Kotlin DSL), D misses file().

❓ lifecycle

advanced

Effect of changing minSdkVersion in build.gradle

If you increase minSdkVersion in your Android build.gradle file, what is the likely effect?

A The app will not run on devices with Android versions below the new minSdkVersion.

B The app will support more devices.

C The app size will automatically decrease.

D The app will run faster on all devices.

💡 Hint

minSdkVersion sets the lowest Android version supported.

Increasing minSdkVersion means devices with older Android versions cannot install or run the app. It does not affect speed or app size directly.

🔧 Debug

expert

Diagnosing build failure due to missing keystore file

You get this error when building a release APK: FileNotFoundException: keystore.jks (No such file or directory). What is the most likely cause?

A The AndroidManifest.xml file is missing required permissions.

B The Flutter SDK is outdated and needs updating.

C The keystore file path in build.gradle is incorrect or the file is missing.

D The Dart code has syntax errors.

💡 Hint

Check the file path and existence of the keystore file.

The error clearly states the keystore file is not found. This usually means the path in build.gradle is wrong or the file is not present. Other options do not cause this error.

Practice

1. What file do you edit to change the Android app ID in a Flutter project?

easy

A. android/gradle.properties

B. lib/main.dart

C. android/app/build.gradle

D. pubspec.yaml

Solution

1. Step 1: Identify where Android app settings are configured

   The Android app ID is set in the Gradle build configuration files.

2. Step 2: Locate the specific file for app-level settings

   The file android/app/build.gradle contains the app ID under the defaultConfig section.

3. Final Answer:

   android/app/build.gradle -> Option C

4. Quick Check:

   App ID set in build.gradle [OK]

Hint: App ID is in app-level build.gradle file [OK]

Common Mistakes:

• Editing pubspec.yaml instead of build.gradle
• Changing main.dart which is for Dart code
• Modifying gradle.properties which is for Gradle settings

2. Which syntax correctly sets the minimum SDK version in android/app/build.gradle?

easy

A. minSdkVersion -> 21

B. minSdkVersion = 21

C. minSdkVersion: 21

D. minSdkVersion 21

Solution

1. Step 1: Understand Gradle syntax for SDK versions

   Gradle uses simple assignment without equals or arrows for SDK versions.

2. Step 2: Identify correct syntax

   The correct syntax is minSdkVersion 21 without equals or colon.

3. Final Answer:

   minSdkVersion 21 -> Option D

4. Quick Check:

   Gradle uses space, not = or : [OK]

Hint: Use space, not equals, for SDK versions in Gradle [OK]

Common Mistakes:

• Using equals sign (=) which causes syntax error
• Using colon (:) which is invalid in Gradle
• Using arrow (->) which is not Gradle syntax

3. Given this snippet in android/app/build.gradle:

defaultConfig {
    applicationId "com.example.app"
    minSdkVersion 19
    targetSdkVersion 33
    versionCode 5
    versionName "1.0.4"
}

What is the app version name that will appear to users?

medium

A. "1.0.4"

B. "1.0.5"

C. "5"

D. "33"

Solution

1. Step 1: Identify versionName in the configuration

   The versionName is set to "1.0.4" which is the user-visible version.

2. Step 2: Differentiate versionCode and versionName

   versionCode is an internal number (5), not shown to users.

3. Final Answer:

   "1.0.4" -> Option A

4. Quick Check:

   versionName is user-visible version [OK]

Hint: versionName shows app version to users [OK]

Common Mistakes:

• Confusing versionCode with versionName
• Using targetSdkVersion as version
• Ignoring quotes around versionName

4. You added minSdkVersion 21 in android/app/build.gradle but get a build error. What is the likely cause?

medium

A. You forgot to update compileSdkVersion to at least 21

B. minSdkVersion must be less than 21

C. You need to add quotes around 21

D. minSdkVersion is set in pubspec.yaml, not build.gradle

Solution

1. Step 1: Understand SDK version dependencies

   The compileSdkVersion must be equal or higher than minSdkVersion.

2. Step 2: Check build.gradle for compileSdkVersion

   If compileSdkVersion is lower than 21, build fails when minSdkVersion is 21.

3. Final Answer:

   You forgot to update compileSdkVersion to at least 21 -> Option A

4. Quick Check:

   compileSdkVersion ≥ minSdkVersion [OK]

Hint: compileSdkVersion must be ≥ minSdkVersion [OK]

Common Mistakes:

• Thinking minSdkVersion must be less than 21
• Adding quotes around numeric SDK versions
• Trying to set minSdkVersion in pubspec.yaml

5. You want to create a new build type called staging in android/app/build.gradle that behaves like debug but with a different app ID suffix. Which snippet correctly adds this?

hard

A. buildTypes {
staging {
extends debug
applicationIdSuffix ".staging"
}
}

B. buildTypes {
staging {
initWith debug
applicationIdSuffix ".staging"
}
}

C. buildTypes {
staging {
copyFrom debug
applicationIdSuffix ".staging"
}
}

D. buildTypes {
staging {
inherit debug
applicationIdSuffix ".staging"
}
}

Solution

1. Step 1: Recall Gradle syntax for copying build types

   Gradle uses initWith to copy settings from another build type.

2. Step 2: Verify correct method and syntax

   initWith debug correctly copies debug settings; applicationIdSuffix ".staging" adds suffix.

3. Final Answer:

   buildTypes { staging { initWith debug applicationIdSuffix ".staging" } } -> Option B

4. Quick Check:

   Use initWith to copy build type [OK]

Hint: Use initWith to clone build types in Gradle [OK]

Common Mistakes:

• Using extends or inherit which are invalid Gradle keywords
• Trying copyFrom which does not exist
• Not adding applicationIdSuffix properly