Here’s a list of Top 50 Flutter Interview Questions and Answers that cover basic to advanced concepts, suitable for both beginners and experienced developers in 2025.
🟢 Beginner Level (1–15)
1. What is Flutter?
Answer: Flutter is an open-source UI toolkit by Google for building natively compiled applications for mobile, web, and desktop from a single codebase using the Dart language.
2. What is Dart?
Answer: Dart is an object-oriented, class-based programming language optimized for UI development, and it’s used by Flutter.
3. What are widgets in Flutter?
Answer: Widgets are the basic building blocks of a Flutter app’s UI. Everything in Flutter is a widget, including layout models and controls.
4. What is the difference between StatelessWidget and StatefulWidget?
Answer: StatelessWidget is immutable (its state can’t change), while StatefulWidget maintains a state that can change over time.
5. What is the pubspec.yaml file used for?
Answer: It manages the Flutter project’s metadata, dependencies, assets, fonts, and more.
6. What is a build() method?
Answer: The build() method describes the part of the UI represented by the widget and is called every time the widget is redrawn.
7. How do you create a new Flutter project?
Answer:
flutter create project_name
8. What is hot reload in Flutter?
Answer: Hot reload allows developers to inject updated source code into the Dart VM while the app is running, preserving the state.
9. What is the difference between runApp() and main()?
Answer: main() is the entry point, and runApp() inflates the widget and attaches it to the screen.
10. What is the purpose of the MaterialApp widget?
Answer: It sets up basic material design visual layout, navigation, and themes.
11. What are keys in Flutter?
Answer: Keys preserve widget state when they move in the widget tree.
12. What is Navigator in Flutter?
Answer: Navigator manages a stack of route objects and allows screen navigation.
13. How to navigate to a new screen in Flutter?
Navigator.push(context, MaterialPageRoute(builder: (context) => SecondScreen()));
14. What are routes in Flutter?
Answer: Routes are the screens/pages in a Flutter app.
15. How do you use packages in Flutter?
Answer: Add the package to pubspec.yaml and run flutter pub get.
🟡 Intermediate Level (16–35)
16. Explain the widget lifecycle in Flutter.
Answer:
createState()initState()didChangeDependencies()build()setState()deactivate()dispose()
17. What is setState() and when is it used?
Answer: It notifies the Flutter framework that the internal state has changed and triggers a rebuild.
18. What is InheritedWidget?
Answer: It allows data to be passed down the widget tree efficiently and is often used for state management.
19. What is FutureBuilder?
Answer: A widget that builds itself based on the latest snapshot of interaction with a Future.
20. What is the use of async/await in Dart?
Answer: It handles asynchronous operations like network calls without blocking the UI thread.
21. How is layout handled in Flutter?
Answer: Flutter uses widgets like Column, Row, Stack, Container, etc., to compose layouts.
22. What is the difference between MainAxisAlignment and CrossAxisAlignment?
Answer: These define alignment along the main and cross axes in Row or Column.
23. How to add images in Flutter?
Answer: Place the image in an assets folder and reference it in pubspec.yaml.
24. What is the difference between hot reload and hot restart?
- Hot reload: Preserves the state.
- Hot restart: Restarts the app and resets the state.
25. What is a Stream?
Answer: A Stream provides a sequence of asynchronous data events.
26. What is the difference between Future and Stream?
- Future: Single async result.
- Stream: Multiple async results over time.
27. What is BLoC in Flutter?
Answer: BLoC (Business Logic Component) is a pattern to separate business logic from UI using Streams and Sinks.
28. What is Provider?
Answer: A recommended state management package that makes data available to widgets below it in the widget tree.
29. What is GetX?
Answer: A lightweight and powerful Flutter package for state management, routing, and dependency injection.
30. How do you manage state in Flutter?
Answer: Using:
setStateProviderBLoCRiverpodGetXCubit
31. What is the difference between final and const in Dart?
- final: Set only once at runtime.
- const: Set at compile time and deeply immutable.
32. What is the difference between SizedBox and Container?
Answer: SizedBox is mainly for giving size; Container provides more styling features.
33. What is Flutter SDK?
Answer: A collection of tools, libraries, and APIs for developing Flutter apps.
34. What is a Scaffold?
Answer: A top-level layout widget that provides app structure (AppBar, Drawer, FAB, etc.)
35. How do you handle errors in Flutter?
Answer: Using try-catch, ErrorWidget, FlutterError.onError, and logging.
🔴 Advanced Level (36–50)
36. How does Flutter achieve native performance?
Answer: By compiling to ARM or x86 native code using Dart’s AOT compiler.
37. Explain how the rendering process works in Flutter.
Answer: It follows Widget -> Element -> RenderObject and uses Skia for rendering.
38. What is the difference between WidgetsBinding and WidgetsBindingObserver?
Answer:
WidgetsBinding: Main glue between framework and engine.WidgetsBindingObserver: Used to listen to lifecycle and system events.
39. What is the use of mixins in Dart?
Answer: They allow sharing code between multiple classes without inheritance.
40. How do you implement internationalization (i18n) in Flutter?
Answer: Using flutter_localizations and intl package.
41. How do you optimize performance in Flutter apps?
- Avoid unnecessary rebuilds.
- Use
constconstructors. - Split large widgets.
- Use lazy loading.
- Minimize overdraw.
42. What is RepaintBoundary?
Answer: It helps Flutter optimize redrawing by isolating parts of the widget tree.
43. How do you test a Flutter app?
Answer:
- Unit tests: For logic.
- Widget tests: For UI.
- Integration tests: For full app behavior.
44. What is FlutterEngine?
Answer: It runs Dart code and manages plugins, assets, and the rendering pipeline.
45. What is platform channel in Flutter?
Answer: It allows Flutter to communicate with native Android (Java/Kotlin) or iOS (Swift/Obj-C) code.
46. What is buildContext in Flutter?
Answer: A handle to the location of a widget in the widget tree.
47. What are isolates in Dart?
Answer: Separate threads of execution that don’t share memory, used for CPU-intensive tasks.
48. What is Riverpod?
Answer: A robust and compile-safe state management library by the creator of Provider.
49. How does Flutter handle memory management?
Answer: Dart uses a generational garbage collector and reference counting under the hood.
50. How do you implement custom animations in Flutter?
Answer: Using AnimationController, Tween, and AnimatedBuilder.
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