Flutter Interview Questions and Answers

Answer: An open-source UI toolkit by Google for building natively compiled applications

Flutter is Google's open-source UI toolkit for building beautiful, natively compiled applications for mobile, web, and desktop from a single codebase.

Answer: Both b and c

RenderObject is the low-level object in Flutter's rendering pipeline. It handles layout calculations, painting, and hit testing. Custom rendering requires extending RenderObject.

Answer: Hot reload preserves state, hot restart doesn't

Hot reload injects updated code while preserving app state. Hot restart completely restarts the app and loses all state. Use hot restart for major structural changes.

Answer: Base class for widgets that efficiently propagate data down the tree

InheritedWidget is a base class for widgets that efficiently propagate information down the tree. Used by Provider, Theme, MediaQuery for data sharing.

Answer: Both b and c

Flutter has three trees: Widget tree (immutable configuration), Element tree (manages widget lifecycle and state), Render tree (handles layout and painting).

Answer: Dart

Flutter uses Dart, a client-optimized programming language developed by Google. Dart is optimized for fast apps on any platform.

Answer: Both b and c

Isolates are independent workers with their own memory heap. They enable true parallelism in Dart. Communicate via message passing. Use for heavy computations.

Answer: Both b and c

Provider is a wrapper around InheritedWidget making it easier to use and more reusable. It is the recommended state management solution by the Flutter team.

Answer: The basic building block of a Flutter app UI

In Flutter, everything is a widget. Widgets are the basic building blocks of a Flutter app's user interface. They describe what their view should look like.

Answer: Both b and c

compute() function runs a function in a separate isolate and returns the result. It simplifies isolate usage for one-off computations without managing isolate lifecycle.

Answer: Stateful and Stateless

Flutter has two main types of widgets: StatelessWidget (immutable, doesn't change) and StatefulWidget (mutable, can change over time based on user interaction or data).

Answer: Both b and c

FutureBuilder builds a widget based on the latest snapshot of a Future. It automatically rebuilds when the Future completes, making async operations easier to handle.

Answer: Both b and c

StreamBuilder builds a widget based on snapshots from a Stream. It automatically rebuilds when new data arrives, perfect for real-time updates.

Answer: Both b and c

const constructors create compile-time constants. Widgets created with const are reused instead of recreated, reducing rebuilds and improving performance.

Answer: Both b and c

RepaintBoundary creates a separate layer for its subtree. When the subtree repaints, it doesn't affect the parent. Used to optimize frequent repaints.

Answer: Notifies the framework that internal state has changed

setState() notifies the Flutter framework that the internal state of a StatefulWidget has changed, triggering a rebuild of the widget with the updated state.

Answer: Preserve widget state when moving in tree

Keys preserve widget state when widgets move in the tree. They help Flutter identify which widgets have changed, are added, or removed. Types include ValueKey, ObjectKey, UniqueKey.

Answer: Both b and c

DevTools timeline is a performance profiling tool showing frame rendering times, GPU usage, memory usage, and widget rebuild information for optimization.

Answer: ListView

ListView is a scrollable list of widgets arranged linearly. It is the most commonly used scrolling widget and automatically provides scrolling when content exceeds viewport.

Answer: Both b and c

GestureDetector detects gestures like tap, double tap, long press, pan, scale, etc. It wraps a widget and provides callbacks for gesture events.

Answer: Both b and c

AnimatedContainer automatically animates between property values over a duration. It is an implicit animation widget that makes animations easy without controllers.

Answer: main()

The main() function is the entry point of every Flutter app. It calls runApp() which inflates the given widget and attaches it to the screen.

Answer: Both b and c

Widget tests (unit tests) test individual widgets in isolation. Integration tests test complete user flows across multiple screens. Both use testWidgets() API.

Answer: A convenience widget that wraps common Material Design widgets

MaterialApp is a convenience widget that wraps a number of widgets commonly required for Material Design applications. It includes Navigator, Theme, and more.