This repository contains common Flutter interview questions and their answers.🚀 From basic to advanced, test your understanding of Flutter and Dart, brush up on your knowledge 💪, or get ready for your next coding interview! I add new questions to this repository on a regular basis (along with answers 😉). Best of luck to all of you. ❤
• Last updated: Nov 8th, 2024
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Flutter is an open-source UI software development toolkit created by Google for building natively compiled applications for mobile, web, and desktop from a single codebase.
Widgets are the building blocks of a Flutter app’s user interface. Everything in Flutter is a widget.
StatelessWidget: A widget that doesn’t change its state over time. StatefulWidget: A widget that maintains state and can rebuild when the state changes.
State refers to the information that can change within a widget and triggers re-rendering to reflect those changes in the UI.
BuildContext is a handle to the location of a widget in the widget tree. It allows access to theme, size, and ancestor widgets.
Keys are used to preserve the state of widgets in scenarios like moving widgets within a list or managing the order of dynamic lists.
setState() is a method used in StatefulWidget to trigger a UI update after modifying the widget's state.
InheritedWidget is used to pass data down the widget tree without needing to pass it explicitly through the constructor of every widget.
Routing in Flutter is managed by the Navigator class, which manages a stack of routes. The push method adds a route to the stack, and the pop method removes it. 100 Flutter Interview Questions and Answers
Navigator 1.0: Traditional stack-based navigation. Navigator 2.0: Supports more complex routing, allowing you to manage the entire stack manually with declarative navigation.
FutureBuilder is a widget that builds itself based on the latest snapshot of a Future, useful for handling async data.
StreamBuilder is a widget that builds itself based on the latest snapshot of a stream of data, typically used for real-time updates.
Scaffold provides the basic structure for a visual interface in Flutter, including app bars, drawers, bottom sheets, and floating action buttons.
Expanded: Forces a widget to take up the available space. Flexible: Allows a widget to take up space but lets it be flexible within the layout constraints.
ListView is a scrollable list of widgets that allows for the efficient display of large datasets. 16. Explain the purpose of SafeArea in Flutter. SafeArea is used to insert padding to avoid system UI elements like notches, status bars, and home screen indicators.
ClipRect is a widget that clips its child to a rectangular area, used to prevent overflow beyond a specific region.
A Hero widget is used for creating shared element transitions between routes.
Spacer takes up the available empty space between widgets, typically used in Row or Column layouts.
GestureDetector is a widget that detects gestures such as taps, swipes, and drags on the screen.
You can handle JSON data using Dart's built-in dart:convert library to parse JSON into Dart objects and vice versa.
Constraints determine how large or small a widget can be in a layout. Every widget must respect its constraints while laying out its children.
A Container is a versatile widget that can be used to apply padding, margins, borders, or background color to its child.
Padding adds empty space around its child widget to create spacing.
Provider is a popular state management solution in Flutter that allows you to share state across your application easily.
ChangeNotifier is a class that helps notify listeners of changes in the state and is used with Provider for state management.
Bloc (Business Logic Component) is a pattern used for managing state in Flutter apps. It separates presentation logic from business logic using streams.
Riverpod is a state management package that improves on Provider, offering more flexibility, testing, and better compile-time safety.
A ValueNotifier is a special type of ChangeNotifier that holds a single value and notifies its listeners when the value changes.
Hot reload: Updates the code without losing the app's state. Hot restart: Restarts the app completely, losing the state.
Mixins allow you to reuse a class’s code across multiple class hierarchies by mixing in behavior.
RenderObject is the base class in Flutter’s rendering pipeline, responsible for layout, painting, and hit-testing of the UI.
The build() method describes the widget structure and is called every time a widget rebuilds.
InheritedWidget is used to pass data down the widget tree to child widgets, making data accessible without passing it through constructor parameters.
EdgeInsets is used to define padding or margin for widgets.
MaterialApp is the top-level widget for building apps that follow Material Design guidelines.
Cupertino is a widget library in Flutter that provides iOS-style widgets for building apps that look and feel native on iOS.
Material: Follows Material Design, typically used for Android apps. Cupertino: Mimics the design of iOS applications, with a Cupertino theme.
ModalRoute is used to display a route that blocks interaction with other routes until it's closed.
WillPopScope is a widget that intercepts the back button press and allows you to control what happens when a user attempts to leave a screen.
WillPopScope is used to intercept the back button press event and allows you to define custom behavior before a user leaves a screen.
Navigator.push: Adds a new route to the navigation stack. Navigator.pushReplacement: Replaces the current route with a new one.
Animations in Flutter can be implemented using the AnimationController, Tween, and AnimatedBuilder classes. Flutter also provides built-in animated widgets like AnimatedContainer, AnimatedOpacity, etc.
A Tween interpolates between the range of values (e.g., from 0 to 1) for animation purposes. It defines how values change over time.
Performance can be optimized by: Using const constructors where possible. Avoiding unnecessary rebuilds with the shouldRebuild method in ListView/GridView. Caching images and reducing widget tree depth. Profiling with Flutter DevTools.
BuildContext is a reference to the location of a widget in the widget tree. It allows you to access various methods and properties, including theme, size, and parent widgets.
InheritedWidget is a base class that passes data down the widget tree without the need to pass it through constructor parameters. It’s useful for state sharing.
A RenderObject is a low-level widget responsible for the layout, painting, hit testing, and other rendering responsibilities.
Offstage is a widget that allows you to hide its child widget from the screen without disposing of it, making it invisible but still in memory.
mainAxisAlignment: Aligns children along the main axis (horizontal for Row, vertical for Column). crossAxisAlignment: Aligns children along the cross axis (vertical for Row, horizontal for Column).
Stream is used to handle asynchronous sequences of data. It emits a sequence of events over time, allowing real-time data processing.
StatefulBuilder is a widget that allows you to rebuild only part of a widget’s tree without rebuilding the entire StatefulWidget.
CustomPaint allows you to draw custom shapes, animations, and complex graphics on the screen using the Canvas API.
Navigation in Flutter is handled using the Navigator class with methods like push, pop, pushReplacement, and declarative routing with Navigator 2.0.
The Hero widget allows you to create smooth transitions between two screens by sharing a common element.
AnimatedBuilder: Provides flexibility to rebuild multiple widgets in the animation without needing to create custom widgets. AnimatedWidget: A simpler way to animate only one widget by extending it.
Container is a convenience widget used to apply padding, margins, borders, alignment, and background colors to its child.
Asynchronous operations in Flutter are managed using Future, async, and await for single asynchronous tasks and Stream for handling a sequence of asynchronous data.
A Future represents a computation that doesn’t complete immediately and will provide a value or an error later.
Responsive layouts can be achieved using widgets like MediaQuery, LayoutBuilder, and Flexible to adapt to different screen sizes.
RenderBox is a class in Flutter responsible for the layout, painting, and hit testing of its box model children.
FractionallySizedBox is a widget that sizes its child relative to its parent based on a fraction of the available space.
ListView.builder creates a lazily built scrollable list, where items are built on-demand, making it efficient for large lists.
TextField is a widget used to receive text input from the user. It can be customized with controllers, validation, styling, and more.
A GlobalKey provides a way to access and manipulate a widget’s state across different parts of the widget tree.
Flutter uses garbage collection to manage memory, releasing unused objects to free up memory.
ThemeData defines the visual theme of your Flutter app, including colors, font styles, icon themes, and more.
Constraints define the minimum and maximum dimensions for a widget, determining its allowable size during the layout phase.
Scrollable is a widget that allows its children to scroll. It is the base class for scrollable views like ListView and GridView.
ExpansionPanelList is a widget that provides a list of panels that can expand and collapse to reveal additional content.
Form is a container for grouping multiple form fields together. It helps with validation and submitting input fields.
Errors can be handled in Flutter using try-catch blocks for synchronous errors, onError for asynchronous operations, and using FlutterError.onError for global error handling.
GestureDetector is used to capture and respond to various user gestures like taps, drags, swipes, and pinches.
Draggable is a widget that allows you to move items around the screen by dragging.
You can create a modal bottom sheet using the showModalBottomSheet function, which displays a sheet that appears from the bottom of the screen.
You can update the state of a widget using setState() inside StatefulWidget to trigger a rebuild of only the affected widget.
Stack is a widget that allows its children to be layered on top of each other, useful for overlays, cards, and floating elements.
SizedBox: A widget that forces a child to have a fixed size. Container: A versatile widget used for layout, styling, and positioning.
CustomScrollView is a scrollable view that allows you to create custom scroll effects with slivers like SliverAppBar and SliverList.
MediaQuery provides information about the size and orientation of the device screen, useful for building responsive layouts.
Cupertino widgets provide iOS-styled user interface components in Flutter, allowing you to create apps that look native on iOS devices.
Data can be passed between screens in Flutter using Navigator.push with arguments or by using a state management solution like Provider.
push: Pushes a route directly using a widget. pushNamed: Pushes a route based on its name, which is defined in a route table.
AppBar is a widget that implements a Material Design app bar, typically used for placing titles, navigation buttons, and other actions.
Drawer is a slide-in navigation panel that provides easy access to a list of navigation items or settings.
SnackBar is a lightweight message bar that briefly displays at the bottom of the screen, often used for notifications or feedback.
FloatingActionButton is a circular button that floats above the content, usually for triggering primary actions.
SharedPreferences is used to store simple key-value pairs persistently across app sessions.
Push notifications in Flutter can be implemented using packages like firebase_messaging for Firebase Cloud Messaging (FCM).
showDialog is a function used to display a modal dialog box.
BoxDecoration is used with Container to apply visual decorations like borders, shadows, and gradients to a widget.
GridView is a widget that displays its children in a grid layout, useful for image galleries or product lists.
Flexible is a widget that allows a child to occupy the available space in a row or column while still respecting other widgets.
Image.network is a widget that loads and displays an image from a network URL.
AspectRatio forces its child to maintain a specific aspect ratio.
Null safety in Flutter is handled by adding ? to variable types that can accept null values, ensuring the compiler can catch null reference errors.
Divider is used to create horizontal or vertical lines between widgets.
Opacity is a widget that changes the transparency of its child widget.
InkWell is a widget that responds to touch events by showing a ripple effect. 100 Flutter Interview Questions and Answers
Timer is used to schedule a callback function to be executed after a certain delay or at regular intervals.