Top 10 flutter interview questions

1. General Flutter Questions Q: What is Flutter, and how does it differ from other cross-platform development frameworks? A: Flutter is a UI toolkit by Google for building natively compiled applications for mobile, web, and desktop from a single codebase. Unlike other frameworks that rely on web-based technologies, Flutter uses its own rendering engine, Skia, which allows it to draw every pixel on the screen, providing high performance and a native feel.

Q: What is a widget in Flutter? Differentiate between Stateless and Stateful Widgets.
A: In Flutter, everything is a widget, which is a basic building block for UI components. StatelessWidget is immutable and does not change once it's built. StatefulWidget maintains a mutable state and can change during the app's lifetime, allowing for dynamic UI updates.

Q: What is BuildContext, and how does it work in Flutter?
A: BuildContext is a handle to the location of a widget in the widget tree. It’s used to look up the widget's position, find dependencies, and access the nearest ancestor widgets.

Q: What are keys in Flutter, and why are they important?
A: Keys are identifiers used to preserve the state of widgets in a list or when widgets change positions. They help Flutter understand which widget instances should be preserved or replaced.

Q: Explain the concept of hot reload and hot restart. How do they differ?
A: Hot reload updates code changes on the fly without losing the app's current state, which is great for fast UI tweaks. Hot restart resets the app to its initial state by reloading the code completely.

1. State Management Q: What is state management, and why is it important in Flutter? A: State management refers to handling the state of the app, such as variables that define the UI or data. It's crucial for maintaining and updating the user interface when data changes.

Q: What state management solutions have you used?
A: Common state management solutions include Provider, Bloc, Riverpod, GetX, and Redux. Each has its strengths; for example, Provider is simple and integrates well with Flutter, while Bloc offers a more structured pattern with event-based state changes.

Q: What is a ChangeNotifier, and how does it help in state management?
A: ChangeNotifier is a part of the Flutter SDK that provides a simple way to manage state. It notifies listeners when there's a change in the state, helping widgets rebuild accordingly.

1. Layout and Widgets Q: Explain the difference between a Container and a SizedBox. A: Container is a versatile widget that can have padding, margin, alignment, and decoration, whereas SizedBox is a simpler widget used primarily for giving a fixed size to its child or spacing between widgets.

Q: How do you create a responsive UI in Flutter?
A: Use MediaQuery for screen dimensions, LayoutBuilder for constraints, and Flexible or Expanded widgets to adapt to different screen sizes. Additionally, AspectRatio helps maintain aspect ratios on different devices.

Q: What are Expanded and Flexible widgets, and how do they work?
A: Both are used to adjust child widgets' space in a Row or Column. Expanded takes up available space proportionally, while Flexible allows a widget to fill the space but can shrink or grow based on the content's needs.

1. Data Handling and Persistence Q: How do you make API calls in Flutter? What packages have you used? A: Use the http package for RESTful API calls. Other packages like dio offer advanced features like interceptors. Use Future and async to handle asynchronous requests.

Q: How would you parse JSON data in Flutter?
A: Use dart:convert to decode JSON into Dart objects using json.decode. For complex JSON, you can use a Model class and factory constructors to parse JSON data.

Q: What is the difference between Future and Stream in Dart?
A: A Future represents a single value that will be available asynchronously, whereas a Stream is a sequence of values delivered over time.

1. Asynchronous Programming and Dart Language Q: How does the asynchronous model in Dart work? Explain Future, async, and await. A: Dart's asynchronous model uses Future for handling async operations. Use async to mark functions that contain asynchronous code and await to pause execution until the Future completes.

Q: What is Isolate in Dart? When would you use it?
A: An Isolate is a separate thread in Dart used for parallelism. Use it for CPU-intensive tasks that can block the main UI thread.

1. Testing and Debugging Q: How do you test a Flutter application? What are the types of tests available? A: Flutter supports unit tests (testing logic), widget tests (testing UI components), and integration tests (testing complete app scenarios). Use packages like flutter_test and mockito.

Q: What are Golden tests, and how are they used in Flutter?
A: Golden tests compare a widget's rendered output to a reference image (a "golden" image). They ensure the UI remains consistent during code changes.

1. Animations and Customizations Q: How do you create animations in Flutter? Explain AnimationController and Tween. A: Use AnimationController to control the animation's duration and lifecycle. Tween defines a value range to animate between. Use AnimatedBuilder or AnimatedWidget to apply the animation to the UI.

Q: What is a Hero animation in Flutter?
A: Hero is a widget that creates a seamless transition between two screens by animating a shared element. It requires matching Hero tags on both source and destination widgets.

1. Performance Optimization Q: What are the best practices to optimize performance in a Flutter app? A: Use const constructors where possible, minimize rebuilds with RepaintBoundary, use ListView.builder for long lists, cache images using CachedNetworkImage, and avoid large widget trees.

Q: What is the RepaintBoundary widget, and how does it help in performance optimization?
A: RepaintBoundary reduces the repaint area when the widget changes. It helps isolate the widget so that only the specified widget is rebuilt instead of the entire screen.

1. Navigation and Architecture Q: How do you implement navigation in Flutter? What are the different navigation methods? A: Use Navigator.push for basic navigation, Navigator.pushNamed for named routes, and Navigator 2.0 for complex routing scenarios with state-based navigation.

Q: Explain various Flutter architectural patterns you've worked with.
A: MVC, MVP, and MVVM are classic patterns for organizing code. Clean Architecture emphasizes separation of concerns, with data, domain, and presentation layers.

1. Advanced Questions Q: How does Flutter handle rendering under the hood? A: Flutter uses its Skia rendering engine to draw UI components directly on the screen, bypassing platform-specific UI components. It uses a widget tree, rendering tree, and layer tree for efficient rendering.

Q: How do you handle platform-specific code in Flutter?
A: Use Platform Channels to communicate between Flutter code and native Android or iOS code. This enables accessing native device features or APIs.