📱 Flutter Interview Questions and Answers (2025)
Basic Level Questions
What is Flutter?
Flutter is an open-source UI software development toolkit by Google used for building natively compiled applications for mobile, web, and desktop from a single codebase.
What programming language does Flutter use?
Flutter apps are written primarily in Dart, a client-optimized programming language for fast apps on any platform.
What is a widget in Flutter?
Widgets are the basic building blocks of a Flutter app’s UI, representing visual components, layout elements, or structural elements.
Explain the difference between Stateful and Stateless Widgets.
Stateless widgets have immutable state once created, while Stateful widgets maintain mutable state that can change during the widget’s lifecycle.
What platforms does Flutter support?
Flutter supports Android, iOS, Web, Windows, macOS, and Linux desktop platforms.
What is the difference between Material and Cupertino widgets?
Material widgets implement Google’s Material Design for Android apps, while Cupertino widgets imitate the iOS design language for Apple platforms.
What is hot reload?
Hot reload allows developers to see code changes reflected instantly in the running app without restarting it or losing the app state.
What is the pubspec.yaml file used for?
It manages the Flutter project’s assets, dependencies, and configurations.
What are keys in Flutter widgets?
Keys preserve widget state when widgets move in the widget tree during rebuilds, essential for stateful widgets in lists.
What is the widget tree?
The widget tree is the hierarchy of widgets that Flutter constructs to render the UI, representing every part of the screen.
Intermediate Level Questions
What is the difference between build() and initState() in a Stateful widget?
initState() is called once when the widget is inserted into the widget tree for initializations, while build() is called multiple times to render the UI.
Explain Flutter’s rendering process.
Flutter uses the widget tree to generate an element tree and a render object tree, which gets painted onto the screen via Skia graphics engine.
What is the purpose of the InheritedWidget?
InheritedWidget allows data to be efficiently propagated down the widget tree, enabling widgets to access shared data.
How does Flutter handle asynchronous programming?
Flutter uses Dart’s async-await syntax, Futures, Streams, and event loops for asynchronous operations.
What is the difference between Future and Stream in Dart?
A Future represents a single asynchronous value or error returned sometime later, whereas a Stream can deliver multiple asynchronous events or values over time.
What are Mixins in Dart and how are they used in Flutter?
Mixins allow the reuse of class code in multiple class hierarchies to compose behaviors without inheritance, commonly used to add functionality.
How do you implement responsive design in Flutter?
Using LayoutBuilder, MediaQuery, and flexible widgets like Expanded and Flexible to create layouts adaptable to different screen sizes.
What is the difference between Navigator.push() and Navigator.pushReplacement()?
Navigator.push() adds a new route onto the stack, Navigator.pushReplacement() replaces the current route with a new one.
What is Flutter’s widget lifecycle?
Key lifecycle methods include createState(), initState(), didUpdateWidget(), build(), deactivate(), and dispose().
How is state management handled in Flutter?
Flutter offers multiple approaches such as setState(), Provider, Bloc, Riverpod, MobX, and Redux to manage application state efficiently.
Advanced Level Questions
Explain the differences between Flutter’s rendering layers: Widgets, Elements, and RenderObjects.
Widgets are immutable configuration objects; Elements are the mutable instances of widgets managing the lifecycle; RenderObjects handle layout, painting, and hit-testing for UI elements.
How does the Flutter engine differ from the Flutter framework?
The Flutter engine is a low-level runtime written in C++ responsible for rendering, gluing platform APIs and Skia graphics, while the framework offers a Dart-based rich set of libraries and widgets.
What are Platform Channels in Flutter?
Platform Channels enable communication between Flutter’s Dart code and native platform code (Java/Swift/Objective-C), allowing access to platform-specific APIs.
Describe how Flutter compiles apps for different platforms.
Flutter uses ahead-of-time (AOT) compilation to produce native ARM or x64 code for mobile and desktop, and just-in-time (JIT) compilation for development to enable hot reload and fast iteration.
How do you optimize Flutter app performance?
By minimizing widget rebuilds, using const constructors, leveraging the widget tree efficiently, avoiding expensive operations in build(), and using efficient rendering techniques.
What is the purpose of the RepaintBoundary widget?
RepaintBoundary creates a separate layer for its child, reducing the repaint area and improving rendering performance.
How does the Provider package simplify state management?
Provider offers a pragmatic way to expose and consume state objects across the widget tree efficiently, integrating with Flutter’s build context and notification system.
Explain the concept of InheritedWidget and how it’s different from Provider.
InheritedWidget is a low-level mechanism to pass data down the widget tree; Provider builds on top of it adding simplicity, type safety, and additional utilities.
What are some techniques for testing Flutter apps?
Flutter supports unit testing, widget testing, and integration testing using the flutter_test package and tooling like the Flutter Driver.
How do you handle platform-specific code in Flutter?
Using Platform Channels, conditional imports, and packages like platform and flutter_platform_widgets to access native platform features.