Flutter Interview Question Basic to Advance 2023

1. What is Flutter?
   Flutter is an open-source mobile application development framework created by Google. It is used to develop cross-platform applications for Android, iOS, and other platforms.
2. What is the programming language used by Flutter?
   Flutter uses the Dart programming language, which is also developed by Google. It is a modern, object-oriented language that is designed for client-side development.
3. What is the difference between Stateful and Stateless widgets?
   Stateful widgets have mutable state, which means their properties can change over time, while Stateless widgets have immutable state, which means they don’t change once they are created.
4. What is the purpose of the “main.dart” file in a Flutter project?
   The main.dart file is the entry point for a Flutter application. It contains the main() function, which is the starting point of the application.
5. What is the purpose of the “pubspec.yaml” file in a Flutter project?
   The pubspec.yaml file is used to manage the dependencies of a Flutter project. It lists all the dependencies that the project needs, and their versions.
6. How do you add an external package in a Flutter project?
   You can add an external package in a Flutter project by adding its name and version to the dependencies section of the pubspec.yaml file, and then running the command “flutter packages get” in the terminal.
7. What is the purpose of the build() method in a widget?
   The build() method is used to build the widget tree that represents the user interface of the application. It returns a widget that describes the user interface, based on the current state of the widget.
8. What is the difference between hot reload and hot restart in Flutter?
   Hot reload updates the state of the running application, while preserving the current state, without restarting the entire application. Hot restart restarts the entire application, and rebuilds the widget tree from scratch.
9. What is the purpose of the “setState()” method in a Stateful widget?
   The setState() method is used to update the state of a Stateful widget. When the state changes, the build() method is called again, and the user interface is updated to reflect the new state.
10. How do you create a new screen in a Flutter application?
    You can create a new screen by creating a new widget, and then navigating to it using the Navigator widget. The Navigator widget is used to manage the navigation stack, and allows you to push and pop screens onto the stack.
11. What is the purpose of the “async” keyword in Dart?
    The async keyword is used to define asynchronous functions. An asynchronous function is a function that doesn’t block the main thread, and allows other code to execute while it is waiting for a result.
12. What is the purpose of the “await” keyword in Dart?
    The await keyword is used to wait for the result of an asynchronous function. When the result is ready, the code after the await keyword is executed.

Intermediate Level Questions:

13. What is a Future in Dart?
    A Future is a value that represents a potentially long-running operation that will complete at some point in the future. It allows you to perform asynchronous operations in Dart.
14. What is a Stream in Dart?
    A Stream is a sequence of asynchronous events. It allows you to receive data asynchronously, and process it as it arrives.
15. What is the purpose of the “async/await” syntax in Dart?
    The async/await syntax allows you to write asynchronous code in a synchronous style. It makes the code more readable and easier to understand.

16. What is the difference between “await” and “then” in Dart?
    “await” waits for the result of an asynchronous operation, while “then” registers a callback function that will be called when the operation completes.

17. What is a StatefulWidget in Flutter?
    A StatefulWidget is a widget that has mutable state. It is used to represent elements of the user interface that can change over time, such as a text input field or a progress bar.

18. What is an InheritedWidget in Flutter?
    An InheritedWidget is a special type of widget that allows you to pass data down the widget tree, from a parent widget to its children. It is used to share data that needs to be accessed by multiple widgets in the tree.

19. What is a Provider in Flutter?
    A Provider is a package that makes it easy to share data between widgets in a Flutter application. It uses the InheritedWidget mechanism to provide access to data throughout the widget tree.

20. How do you handle user input in a Flutter application?
    You can handle user input by attaching event handlers to widgets, such as onTap() for a button or onChanged() for a text input field. These event handlers are functions that are called when the user interacts with the widget.

21. What is the purpose of the “GestureDetector” widget in Flutter?
    The GestureDetector widget is used to detect gestures, such as taps, swipes, and long presses, on a widget. It allows you to attach event handlers to these gestures and respond to them.

22. What is the purpose of the “Navigator” widget in Flutter?
    The Navigator widget is used to manage the navigation stack in a Flutter application. It allows you to push and pop screens onto the stack, and navigate between them.

23. How do you pass data between screens in a Flutter application?
    You can pass data between screens by passing it as arguments to the Navigator.push() method when navigating to a new screen. The data can be accessed in the new screen using the ModalRoute.of(context).settings.arguments property.

24. What is the purpose of the “FutureBuilder” widget in Flutter?
    The FutureBuilder widget is used to asynchronously build a widget tree based on the result of a Future. It allows you to display a loading indicator while the Future is running, and then display the result when it is ready.

25. What is the purpose of the “Tween” class in Flutter?
    The Tween class is used to define the range of values that an animation should interpolate between. It is used in conjunction with the AnimationController class to define the animation.

26. What is the purpose of the “AnimatedBuilder” widget in Flutter?
    The AnimatedBuilder widget is used to build a widget tree based on an animation. It allows you to specify the child widget that should be animated, and the animation itself.

27. What is the purpose of the “AnimatedWidget” class in Flutter? The AnimatedWidget class is used to create custom widgets that are animated based on a specific animation. It allows you to separate the animation logic from the widget tree.

28. What is the purpose of the “Hero” widget in Flutter?
    The Hero widget is used to animate a widget from one screen to another. It allows you to create a smooth transition between screens, by animating the widget’s size, position, and appearance.

29. What is the purpose of the “StreamBuilder” widget in Flutter?

    The StreamBuilder widget is used to asynchronously build a widget tree based on the events of a Stream. It allows you to display a loading indicator while the Stream is running, and then display the data as it arrives.

30. What is the purpose of the “AnimationController” class in Flutter?
    The AnimationController class is used to control animations in a Flutter application. It allows you to define the duration and curve of an animation, and start, stop, and reverse it.
31. What is the purpose of the “AnimatedSwitcher” widget in Flutter?
    The AnimatedSwitcher widget is used to animate the transition between two or more widgets when they are swapped out. It allows you to create a smooth transition between the widgets, by animating their size, position, and appearance.
32. How do you handle screen orientation changes in a Flutter application?
    You can handle screen orientation changes by attaching an event handler to the OrientationBuilder widget. This widget provides a callback function that is called whenever the orientation changes, allowing you to update the user interface accordingly.
33. What is the purpose of the “LayoutBuilder” widget in Flutter?
    The LayoutBuilder widget is used to build a widget tree based on the size of its parent widget. It allows you to create a responsive user interface that adapts to different screen sizes.
34. What is the purpose of the “ClipRect” widget in Flutter?
    The ClipRect widget is used to clip a child widget to the bounds of its parent widget. It allows you to create custom shapes and sizes for your widgets.
35. What is the purpose of the “ClipPath” widget in Flutter?
    The ClipPath widget is used to clip a child widget to a custom shape defined by a Path object. It allows you to create complex shapes and animations for your widgets.
36. What is the purpose of the “CustomPainter” class in Flutter?
    The CustomPainter class is used to draw custom graphics and animations on a canvas. It allows you to define the shape, size, and appearance of your widgets.
37. What is the purpose of the “CustomClipper” class in Flutter?
    The CustomClipper class is used to create custom clipping paths for your widgets. It allows you to define complex shapes and animations that can be applied to your widgets.
38. What is the purpose of the “Scrollbar” widget in Flutter?
    The Scrollbar widget is used to provide a visual indicator of the position of a scrollable widget. It allows the user to quickly navigate to a specific position in the widget.
39. What is the purpose of the “NotificationListener” widget in Flutter?
    The NotificationListener widget is used to listen for notifications from child widgets. It allows you to respond to specific notifications, such as when a scrollable widget is scrolled.
40. What is the purpose of the “ValueListenableBuilder” widget in Flutter?
    The ValueListenableBuilder widget is used to build a widget tree based on the value of a ValueNotifier object. It allows you to create custom widgets that react to changes in the value of the object.
41. What is the purpose of the “ValueNotifier” class in Flutter?
    The ValueNotifier class is used to hold a value that can be observed by multiple widgets. It allows you to create widgets that react to changes in the value of the object.
42. What is the purpose of the “AsyncSnapshot” class in Flutter?
    The AsyncSnapshot class is used to hold the result of an asynchronous operation. It allows you to handle different states of the operation, such as when it is loading, completed.
43. What is the purpose of the “FadeTransition” widget in Flutter?
    The FadeTransition widget is used to create a smooth fade animation between two or more widgets. It allows you to specify the duration and curve of the animation.
44. What is the purpose of the “SlideTransition” widget in Flutter?
    The SlideTransition widget is used to create a smooth slide animation between two or more widgets. It allows you to specify the direction, duration, and curve of the animation.
45. What is the purpose of the “ScaleTransition” widget in Flutter?
    The ScaleTransition widget is used to create a smooth scale animation between two or more widgets. It allows you to specify the duration, curve, and alignment of the animation.
46. What is the purpose of the “RotationTransition” widget in Flutter?
    The RotationTransition widget is used to create a smooth rotation animation between two or more widgets. It allows you to specify the duration, curve, and alignment of the animation.
47. What is the purpose of the “Hero” widget in Flutter?
    The Hero widget is used to create a smooth transition animation between two widgets with the same tag. It allows you to create visually appealing user interfaces with seamless transitions between screens.
48. What is the purpose of the “LayoutDelegate” class in Flutter?
    The LayoutDelegate class is used to define the layout of a widget that uses a custom layout algorithm. It allows you to define the size and position of child widgets based on the size of the parent widget.
49. What is the purpose of the “AspectRatio” widget in Flutter?
    The AspectRatio widget is used to enforce a specific aspect ratio for a child widget. It allows you to maintain the proportions of the child widget regardless of the size of its parent widget.
50. What is the purpose of the “OverflowBox” widget in Flutter?
    The OverflowBox widget is used to allow a child widget to overflow the bounds of its parent widget. It allows you to create custom designs that break the boundaries of the parent widget.
51. What is the purpose of the “FractionallySizedBox” widget in Flutter?
    The FractionallySizedBox widget is used to size a child widget based on a fraction of the size of its parent widget. It allows you to create responsive user interfaces that adapt to different screen sizes.
52. What is the purpose of the “SizedBox” widget in Flutter?
    The SizedBox widget is used to enforce a specific size for a child widget. It allows you to create widgets with a fixed width and height.
53. What is the purpose of the “FittedBox” widget in Flutter?
    The FittedBox widget is used to scale a child widget to fit within the bounds of its parent widget. It allows you to maintain the aspect ratio of the child widget while adjusting its size.
54. What is the purpose of the “LimitedBox” widget in Flutter?
    The LimitedBox widget is used to limit the maximum size of a child widget. It allows you to create layouts that prevent widgets from growing too large.
55. What is the purpose of the “IntrinsicWidth” widget in Flutter?
    The IntrinsicWidth widget is used to determine the minimum width required by a child widget. It allows you to create layouts that accommodate widgets with different widths.
56. What is the purpose of the “IntrinsicHeight” widget in Flutter?
    The IntrinsicHeight widget is used to determine the minimum height required by a child widget. It allows you to create layouts that accommodate widgets with different heights.
57. What is the purpose of the “Spacer” widget in Flutter?
    The Spacer widget is used to create a flexible space between widgets in a layout. It allows you to distribute the available space evenly between the widgets.
58. What is the purpose of the “ListView” widget in Flutter?
    The ListView widget is used to display a scrolling list of widgets. It allows you to efficiently display a large number of items without requiring excessive memory usage.
59. What is the purpose of the “GridView” widget in Flutter?
    The GridView widget is used to display a grid of widgets. It allows you to efficiently display a large number of items in a compact, organized layout.
60. What is the purpose of the “SliverList” widget in Flutter?
    The SliverList widget is used to display a scrolling list of widgets within a SliverAppBar or CustomScrollView. It allows you to efficiently display a large number of items within a flexible, scrollable layout.
61. What is the purpose of the “SliverGrid” widget in Flutter?
    The SliverGrid widget is used to display a grid of widgets within a SliverAppBar or CustomScrollView. It allows you to efficiently display a large number of items in a compact, organized layout within a flexible, scrollable layout.
62. What is the purpose of the “ScrollController” class in Flutter?
    The ScrollController class is used to control the scrolling behavior of a scrolling list or other layout. It allows you to programmatically scroll to a specific position, listen for scroll events, and customize the scrolling behavior based on user interactions or other events.
63. What is the purpose of the “RefreshIndicator” widget in Flutter?
    The RefreshIndicator widget is used to provide pull-to-refresh functionality within a scrolling list or another layout. It allows users to pull down on the screen to refresh the content within the layout.
64. What is the purpose of the “Scrollbar” widget in Flutter?
    The Scrollbar widget is used to provide a visual indication of the position within a scrolling list or another layout. It allows users to quickly navigate to a specific position within the layout.
65. What is the purpose of the “SingleChildScrollView” widget in Flutter?
    The SingleChildScrollView widget is used to create a scrollable widget that contains a single child widget. It allows you to display content that exceeds the size of the screen in a scrollable container.
66. What is the purpose of the “CustomScrollView” widget in Flutter?
    The CustomScrollView widget is used to create a highly customizable scrollable widget that can contain multiple types of child widgets, including Slivers. It allows you to create complex scrolling layouts with custom behavior and appearance.
67. What is the purpose of the “IndexedStack” widget in Flutter?
    The IndexedStack widget is used to display a stack of widgets where only one child is visible at a time based on an index. It allows you to efficiently switch between multiple child widgets without having to rebuild them each time.
68. What is the purpose of the “AnimatedContainer” widget in Flutter?
    The AnimatedContainer widget is used to create a container widget that can animate changes to its properties, such as size, position, and color. It allows you to create dynamic and engaging UIs with smooth and fluid animations.
69. What is the purpose of the “AnimatedOpacity” widget in Flutter?
    The AnimatedOpacity widget is used to animate changes to the opacity of a child widget. It allows you to create smooth transitions between two states of a widget, such as showing or hiding a widget.
70. What is the purpose of the “AnimatedBuilder” widget in Flutter?
    The AnimatedBuilder widget is used to create custom animations by combining multiple animated values with a builder function. It allows you to create complex animations with reusable code.
71. What is the purpose of the “Hero” widget in Flutter?
    The Hero widget is used to create a shared element transition between two screens. It allows you to smoothly animate a widget from one screen to another, creating a seamless and immersive user experience.
72. What is the purpose of the “ClipRect” widget in Flutter?
    The ClipRect widget is used to clip a child widget to a rectangular shape. It allows you to create custom shapes and masks for your widgets.
73. What is the purpose of the “ClipOval” widget in Flutter?
    The ClipOval widget is used to clip a child widget to a circular shape. It allows you to create circular images and other custom circular shapes.
74. What is the purpose of the “ClipPath” widget in Flutter?
    The ClipPath widget is used to clip a child widget to a custom path. It allows you to create complex and custom shapes for your widgets.
75. What is the purpose of the “LayoutBuilder” widget in Flutter?
    The LayoutBuilder widget is used to build a widget tree based on the size and constraints of its parent widget. It allows you to create responsive and dynamic layouts that adapt to changes in screen size and orientation.
76. What is the purpose of the “AspectRatio” widget in Flutter?
    The AspectRatio widget is used to constrain the aspect ratio of a child widget. It allows you to ensure that a widget maintains a specific aspect ratio regardless of its size or the size of its parent.
77. What is the purpose of the “StreamBuilder” widget in Flutter?
    The StreamBuilder widget is used to display a widget that updates based on events emitted by a stream. It allows you to create reactive and real-time UIs that update automatically as data changes.
78. What is the purpose of the “FutureBuilder” widget in Flutter?
    The FutureBuilder widget is used to display a widget that depends on the result of a Future. It allows you to create responsive and dynamic UIs that respond to asynchronous data loading.
79. What is the purpose of the “InheritedWidget” class in Flutter?
    The InheritedWidget class is used to provide data to child widgets that need access to it. It allows you to create efficient and performant data sharing between multiple widgets without having to pass data down the widget tree explicitly.
80. What is the purpose of the “AnimatedList” widget in Flutter?
    The AnimatedList widget is used to create a scrolling list of items that can be added or removed with smooth and fluid animations. It allows you to create dynamic and engaging UIs that respond to user input.
81. What is the purpose of the “Dismissible” widget in Flutter?
    The Dismissible widget is used to create a widget that can be swiped away in a specific direction. It allows you to create interactive and intuitive UIs that respond to user input.
82. What is the purpose of the “GestureDetector” widget in Flutter?
    The GestureDetector widget is used to detect gestures made by the user, such as taps, swipes, and long presses. It allows you to create custom and interactive UIs that respond to user input.
83. What is the purpose of the “Draggable” widget in Flutter?
    The Draggable widget is used to create a widget that can be dragged and dropped within a specific area. It allows you to create custom and interactive UIs that respond to user input.
84. What is the purpose of the “DragTarget” widget in Flutter?
    The DragTarget widget is used to create a widget that can accept a draggable widget dropped onto it. It allows you to create custom and interactive UIs that respond to user input.
85. What is the purpose of the “InkWell” widget in Flutter?
    The InkWell widget is used to create a widget that responds to taps with an ink splash effect. It allows you to create interactive and engaging UIs that respond to user input.
86. What is the purpose of the “flutter_bloc” library in Flutter?
    The flutter_bloc library is used to implement the BLoC (Business Logic Component) architecture in Flutter apps. It allows you to separate the presentation logic from the business logic in your app, making it easier to test, maintain, and scale.
87. What is the BLoC pattern in Flutter?
    The BLoC (Business Logic Component) pattern is an architecture pattern that separates the business logic of an application from the presentation layer. It allows for better separation of concerns and makes it easier to test, maintain and scale the application.
88. How does the flutter_bloc library help in implementing the BLoC pattern in Flutter?
    The flutter_bloc library provides tools and utilities to implement the BLoC pattern in Flutter apps. It provides a set of classes, including Bloc, BlocProvider, and BlocBuilder, that help in creating and managing BLoCs.
89. What is a BlocProvider in the flutter_bloc library?
    BlocProvider is a widget provided by the flutter_bloc library that creates a BLoC and provides it to the widget tree below it. It is used to ensure that all the widgets in the subtree can access the same instance of the BLoC.
90. What is the BlocBuilder in the flutter_bloc library?
    BlocBuilder is a widget provided by the flutter_bloc library that rebuilds its child widget in response to state changes in the BLoC. It is used to update the UI based on the latest state of the BLoC.
91. What is the difference between a Bloc and a Cubit in the flutter_bloc library?
    Both Bloc and Cubit are classes provided by the flutter_bloc library that help in implementing the BLoC pattern in Flutter apps. The main difference between the two is that a Bloc has events and states while a Cubit only has a state.
92. What is the purpose of the emit method in the flutter_bloc library?
    The emit method is used to emit a new state from the BLoC. It is used to update the state of the BLoC and trigger a rebuild of the widgets that are listening to it.
93. What is the purpose of the listen method in the flutter_bloc library?
    The listen method is used to listen to state changes in the BLoC. It is used to update the UI in response to changes in the state of the BLoC.
94. How do you test a BLoC in the flutter_bloc library?
    You can test a BLoC in the flutter_bloc library by creating a test file and writing tests for each of the methods in the BLoC. You can use the TestBloc class provided by the flutter_bloc library to test the BLoC.
95. What are the advantages of using the BLoC pattern in Flutter apps?
    The advantages of using the BLoC pattern in Flutter apps include better separation of concerns, easier testing and maintenance, and better scalability.
96. Can you implement the BLoC pattern without using the flutter_bloc library? Yes, you can implement the BLoC pattern in Flutter apps without using the flutter_bloc library. However, using the library makes it easier and faster to implement the pattern and provides several utilities and tools that make the implementation more robust and efficient.
97. What is the GetX library in Flutter?
    GetX is a lightweight, open-source library for Flutter that provides a simple and efficient way to manage state, navigation, and dependency injection in Flutter apps.
98. What are the main features of the GetX library?
    The main features of the GetX library include state management, navigation management, dependency injection, and internationalization.
99. How does the GetX library help in state management in Flutter?
    The GetX library provides an elegant way to manage state in Flutter apps using the powerful reactive programming paradigm. It uses the concept of observables, streams, and reactive programming to simplify state management in Flutter apps.
100. What is dependency injection in Flutter and how does the GetX library help in it?
     Dependency injection is a technique in software engineering that allows you to inject dependencies into a class or object. The GetX library provides a simple and efficient way to implement dependency injection in Flutter apps. It uses the concept of lazy loading to load dependencies only when needed and makes the implementation of dependency injection more efficient.
101. What is the purpose of the GetBuilder widget in GetX library?
     The GetBuilder widget is a simple widget provided by the GetX library that allows you to rebuild only the widget that needs to be updated. It is used to update the UI based on the latest state of the observable variable.
102. How does the GetX library help in navigation management in Flutter?
     The GetX library provides a simple and efficient way to manage navigation in Flutter apps. It uses the concept of named routes and provides a set of methods and utilities to navigate between screens in the app.
103. What is the purpose of the GetXController in GetX library?
     The GetXController is a class provided by the GetX library that allows you to manage the state of a widget or an entire app. It is used to create and manage observables, streams, and reactive programming in Flutter apps.
104. How do you test an app using the GetX library?
     You can test an app using the GetX library by creating a test file and writing tests for each of the methods in the app. You can use the TestWidgets class provided by the Flutter framework to test the app.
105. What are the advantages of using the GetX library in Flutter apps?
     The advantages of using the GetX library in Flutter apps include simple and efficient state management, navigation management, and dependency injection. It also provides better performance and makes it easier to write testable and maintainable code.
106. Can you use the GetX library with other state management libraries in Flutter?
     Yes, you can use the GetX library with other state management libraries in Flutter, such as Provider or BLoC. However, using the GetX library as a standalone library provides several benefits and makes the implementation more efficient and robust.