Flutter is one of the most popular cross-platform development frameworks, and landing a job as a Flutter developer requires deep knowledge of its core concepts. Whether you’re preparing for an interview or brushing up on your skills, this guide covers the most commonly asked Flutter interview questions with detailed explanations.
1. What is FFI in Flutter, and why is it used?
FFI (Foreign Function Interface) in Flutter allows Dart code to call native C APIs directly without using platform channels. It’s commonly used for performance optimization, accessing system-level libraries, and integrating with native code.
2. Have you built Flutter plugins or packages? Describe your approach.
Creating plugins or packages involves writing Dart and platform-specific code (Java/Kotlin for Android and Swift/Objective-C for iOS). The process includes:
- Setting up the package using
flutter create --template=plugin. - Writing native platform code to expose desired functionalities.
- Implementing a Dart API to interact with the native code.
- Publishing the package on pub.dev if open-source.
3. Isar DB vs. SQFlite: Which One to Choose for Local Storage in Flutter?
Isar DB is a NoSQL database optimized for Flutter with high-speed performance, while SQFlite is a relational database based on SQLite.
- Isar DB is faster, supports queries in Dart, and doesn’t require async transactions.
- SQFlite is widely used, SQL-based, and suitable for complex relational data.
Implementation:
- For SQFlite: Use
sqflitepackage. - For Isar DB: Use
isarpackage.
4. What are Build Flavors in Flutter?
Build flavors allow developers to create different versions of an app (e.g., dev, staging, production) with separate configurations. In Android, this is done via build.gradle, and in iOS, using xcconfig files.
5. Best Ways to Optimize a Flutter App
- Use const constructors wherever possible.
- Implement lazy loading using
ListView.builder(). - Reduce widget rebuilds using
ProviderorRiverpod. - Minimize widget tree depth.
- Optimize images with
cached_network_image.
6. How Do You Add a Flutter App to an Existing Android App?
Flutter can be embedded in an existing Android app as a module:
- Add Flutter module using
flutter create -t module. - Link the module using Gradle.
- Launch Flutter from native code with
FlutterActivity.
7. What is Tree Shaking in Flutter?
Tree shaking is an optimization technique that removes unused code to reduce the app’s final size. Flutter does this automatically in release mode using Dart’s compiler.
8. Explain the Widget Tree and Other Trees in Flutter
Besides the Widget Tree, Flutter has:
- Element Tree: Represents instantiated widget instances.
- Render Tree: Handles painting and layout.
9. What’s the Difference Between Widgets and Slivers in Flutter?
- Widgets: Basic UI components.
- Slivers: Scrollable areas that dynamically render only visible content.
- Example:
ListViewvs.CustomScrollViewwith slivers.
10. Explain Intrinsic Widgets in Flutter
Intrinsic widgets measure their children before layout. Examples:
IntrinsicHeightIntrinsicWidth
11. What is Canvas in Flutter?
Canvas is used in CustomPaint for drawing custom UI elements. It’s part of Flutter’s rendering pipeline and provides low-level drawing capabilities.
12. What are RenderObjects in Flutter?
RenderObjects are responsible for layout, painting, and hit detection in Flutter. Most developers use higher-level abstractions, but knowing RenderObjects helps when dealing with low-level UI customization.
13. How Do You Ensure Separation of Concerns in Flutter?
By following:
- MVVM or Clean Architecture.
- Using state management like Bloc, Provider, or Riverpod.
- Keeping UI and business logic separate.
14. How Do You Plan Work Before Writing Code?
- Define project requirements.
- Break tasks into smaller components.
- Use UML diagrams or flowcharts.
- Create a proof-of-concept prototype.
15. What’s the Testing Process in Flutter?
Testing ensures quality before release. Types include:
- Unit Testing: Testing functions and methods.
- Widget Testing: Ensures UI renders correctly.
- Integration Testing: Tests the full app.
Bonus: ListView vs. SingleChildScrollView vs. CustomScrollView
SingleChildScrollView: Renders all children at once (bad for large lists).ListView.builder(): Efficiently renders visible items only.CustomScrollView: Uses slivers for nested lists and complex scrolling.
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Conclusion
Mastering these Flutter interview questions will help you stand out in technical interviews. Keep practising and stay updated with Flutter’s evolving ecosystem. Happy coding!
