Part 1: Beginner Level (Q1–Q20)
1. What is Flutter?
Answer:
Flutter is an open-source UI software development kit (SDK) created by Google. It is used to build natively compiled applications for mobile, web, and desktop from a single codebase.
1. What is Flutter?
Answer:
Flutter is an open-source UI software development kit (SDK) created by Google. It is used to build natively compiled applications for mobile, web, and desktop from a single codebase.
2. What programming language does Flutter use?
Answer:
Flutter uses the Dart programming language, also developed by Google. Dart is optimized for UI development and supports Ahead-of-Time (AOT) and Just-in-Time (JIT) compilation.
3. What are the main advantages of Flutter?
Answer:
-
Single codebase for multiple platforms
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Fast development with Hot Reload
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High performance close to native
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Rich UI with customizable widgets
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Strong community and Google support
4. What is Hot Reload in Flutter?
Answer:
Hot Reload allows developers to instantly see code changes in the app without restarting it. It helps speed up development and preserves app state.
5. What is a Widget in Flutter?
Answer:
Everything in Flutter is a widget. Widgets describe what the UI should look like. Buttons, text, images, layouts—everything is a widget.
6. What are the types of widgets in Flutter?
Answer:
-
StatelessWidget – UI does not change
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StatefulWidget – UI changes dynamically based on state
7. What is StatelessWidget?
Answer:
A StatelessWidget is immutable. Once built, it cannot change its state during runtime.
8. What is StatefulWidget?
Answer:
A StatefulWidget can rebuild itself when its internal state changes using the setState() method.
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| StatelessWidget Vs StatefulWidget |
9. What is setState() in Flutter?
Answer:
setState() tells Flutter that the widget’s state has changed and the UI needs to be rebuilt.
10. What is BuildContext?
Answer:
BuildContext is a reference to the location of a widget in the widget tree. It is used to access theme, media query, navigator, and inherited widgets.
11. What is a Scaffold widget?
Answer:
Scaffold provides a basic structure for an app, including:
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AppBar
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Body
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Drawer
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FloatingActionButton
12. What is MaterialApp?
Answer:
MaterialApp is the root widget that provides material design functionality like themes, routes, and localization.
13. What is Cupertino in Flutter?
Answer:
Cupertino widgets are used to create iOS-style UI components such as CupertinoButton and CupertinoNavigationBar.
14. What is pubspec.yaml?
Answer:
pubspec.yaml is a configuration file used to manage:
-
Dependencies
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Assets
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Fonts
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App metadata
15. What are assets in Flutter?
Answer:
Assets are external files such as images, JSON, and fonts used in the app. They must be declared in pubspec.yaml.
16. What is a Column widget?
Answer:
Column arranges widgets vertically from top to bottom.
17. What is a Row widget?
Answer:
Row arranges widgets horizontally from left to right.
18. What is Expanded widget?
Answer:
Expanded forces a widget to take available space inside a Row or Column.
19. What is Padding widget?
Answer:
Padding adds empty space around a widget using EdgeInsets.
20. What is Center widget?
Answer:
Center aligns its child widget in the middle of the screen or parent widget.
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| Flutter Architecture |
📘 Flutter Interview Questions & Answers
Part 2: Intermediate Level (Q21–Q40)
21. What is the Widget Tree in Flutter?
Answer:
The Widget Tree is a hierarchical structure of widgets in a Flutter app. Every widget has a parent and possibly children, forming a tree that describes the UI.
22. What is the Element Tree?
Answer:
The Element Tree manages the relationship between widgets and render objects. It handles widget lifecycle and updates efficiently.
23. What is the Render Tree?
Answer:
The Render Tree is responsible for layout, painting, and hit testing of widgets on the screen.
24. What is State Management in Flutter?
Answer:
State management is the process of managing and updating UI data efficiently across widgets in an application.
25. What are common State Management approaches?
Answer:
-
setState
-
Provider
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Riverpod
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Bloc / Cubit
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GetX
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Redux
26. What is Provider in Flutter?
Answer:
Provider is a wrapper around InheritedWidget that simplifies state management and improves code scalability and performance.
27. What is InheritedWidget?
Answer:
InheritedWidget allows data to be efficiently passed down the widget tree without rebuilding unnecessary widgets.
28. What is Bloc pattern?
Answer:
Bloc (Business Logic Component) separates UI from business logic using streams and events for better maintainability.
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| State Management approaches |
29. What is Cubit?
Answer:
Cubit is a simplified version of Bloc that uses functions instead of events to manage state.
30. What is Navigation in Flutter?
Answer:
Navigation refers to moving between screens using the Navigator widget and routes.
31. What are Routes in Flutter?
Answer:
Routes are screens or pages in an app. Flutter supports:
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Named routes
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Anonymous routes
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Generated routes
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| Navigation |
32. What is Navigator.push()?
Answer:
Navigator.push() adds a new route to the navigation stack and navigates to a new screen.
33. What is Navigator.pop()?
Answer:
Navigator.pop() removes the current route and returns to the previous screen.
34. What is ListView?
Answer:
ListView is a scrollable list of widgets used to display items vertically or horizontally.
35. Difference between ListView and ListView.builder()?
Answer:
-
ListViewloads all items at once -
ListView.builder()builds items lazily, improving performance for large lists
36. What is GridView?
Answer:
GridView displays items in a two-dimensional grid layout.
37. What is SingleChildScrollView?
Answer:
SingleChildScrollView allows scrolling for a single widget when content overflows.
38. What is Form widget?
Answer:
Form groups form fields and allows validation and submission of user input.
39. What is TextFormField?
Answer:
TextFormField is an input field used inside a Form widget and supports validation.
40. What is MediaQuery?
Answer:
MediaQuery provides information about device size, orientation, and screen density for responsive design.
📘 Flutter Interview Questions & Answers
Part 3: Advanced-Intermediate Level (Q41–Q60)
41. What is asynchronous programming in Flutter?
Answer:
Asynchronous programming allows tasks to run without blocking the main UI thread. Flutter uses Future, async, and await keywords to handle async operations.
42. What is a Future in Dart?
Answer:
A Future represents a value that will be available at some point in the future, such as API responses or database calls.
43. What is async and await?
Answer:
-
asyncmarks a function as asynchronous -
awaitpauses execution until the Future completes
44. What is a Stream in Flutter?
Answer:
A Stream provides a sequence of asynchronous data events over time, such as real-time updates or continuous data flow.
45. Difference between Future and Stream?
Answer:
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Future → Single value or error
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Stream → Multiple values over time
46. What is StreamBuilder?
Answer:
StreamBuilder is a widget that rebuilds UI based on the latest data from a stream.
47. What is FutureBuilder?
Answer:
FutureBuilder builds widgets based on the state of a Future (loading, success, error).
48. What is REST API integration in Flutter?
Answer:
REST API integration allows Flutter apps to communicate with backend servers using HTTP requests like GET, POST, PUT, and DELETE.
49. Which package is commonly used for HTTP requests?
Answer:
The http package is commonly used for making network requests in Flutter.
50. What is JSON serialization?
Answer:
JSON serialization is the process of converting JSON data into Dart objects and vice versa.
51. What is jsonDecode()?
Answer:
jsonDecode() converts a JSON string into a Dart Map or List.
52. What is jsonEncode()?
Answer:
jsonEncode() converts a Dart object into a JSON string.
53. What is error handling in Flutter?
Answer:
Error handling is managing exceptions using try, catch, and finally blocks to prevent app crashes.
54. What is Dio package?
Answer:
Dio is an advanced HTTP client that supports interceptors, global configuration, form data, and request cancellation.
55. What is Null Safety in Flutter?
Answer:
Null Safety prevents null reference errors by distinguishing nullable and non-nullable variables at compile time.
56. What is late keyword?
Answer:
The late keyword tells Dart that a variable will be initialized later before use.
57. What is ? and ! in Dart?
Answer:
-
?→ Nullable variable -
!→ Null assertion operator
58. What is mounted in StatefulWidget?
Answer:
mounted checks whether a widget is still in the widget tree before calling setState().
59. What is lifecycle of StatefulWidget?
Answer:
-
createState()
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initState()
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build()
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didUpdateWidget()
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dispose()
60. What is dispose() method used for?
Answer:
dispose() releases resources such as controllers, streams, and listeners to avoid memory leaks.
📘 Flutter Interview Questions & Answers
Part 4: Advanced Level (Q61–Q80)
61. What is Flutter Architecture?
Answer:
Flutter architecture consists of three main layers:
-
Framework (Dart)
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Engine (C++ & Skia)
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Embedder (Platform-specific code)
62. What is Flutter Engine?
Answer:
The Flutter Engine is written in C++ and handles rendering, text layout, and communication with native APIs.
63. What is Skia?
Answer:
Skia is a 2D graphics engine used by Flutter to render UI consistently across platforms.
64. What is a Custom Widget?
Answer:
A custom widget is created by combining existing widgets to build reusable UI components.
65. What is RepaintBoundary?
Answer:
RepaintBoundary isolates a widget’s repaint area to improve rendering performance.
66. What is const constructor?
Answer:
A const constructor creates compile-time constants and improves performance by reusing widget instances.
67. How do you improve Flutter app performance?
Answer:
-
Use const widgets
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Avoid unnecessary rebuilds
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Use ListView.builder
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Optimize images
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Use RepaintBoundary
68. What are Keys in Flutter?
Answer:
Keys help Flutter identify widgets uniquely when rebuilding UI, especially in lists.
69. Types of Keys in Flutter?
Answer:
-
ValueKey
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ObjectKey
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UniqueKey
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GlobalKey
70. What is GlobalKey?
Answer:
GlobalKey allows access to a widget’s state and context across the widget tree.
71. What is Animation in Flutter?
Answer:
Animation in Flutter is the process of creating motion and visual effects using the animation framework.
72. What is AnimationController?
Answer:
AnimationController controls the animation duration, direction, and state.
73. What is Tween?
Answer:
Tween defines the range of values for an animation (e.g., from 0.0 to 1.0).
74. What is AnimatedBuilder?
Answer:
AnimatedBuilder rebuilds only the animated widget, improving performance.
75. What is Hero animation?
Answer:
Hero animation creates smooth transitions between screens for shared UI elements.
76. What are Platform Channels?
Answer:
Platform Channels allow Flutter to communicate with native Android (Kotlin/Java) and iOS (Swift/Obj-C) code.
77. What is MethodChannel?
Answer:
MethodChannel is used to invoke native platform methods from Flutter.
78. What is EventChannel?
Answer:
EventChannel provides continuous data streams from native platforms to Flutter.
79. What is Isolate in Flutter?
Answer:
An Isolate is a separate thread for performing heavy computation without blocking the UI.
80. What is compute() function?
Answer:
compute() runs a function in a background isolate to improve performance for expensive tasks.
📘 Flutter Interview Questions & Answers
Part 5: Expert / Real Interview Level (Q81–Q100)
81. What is Flutter testing?
Answer:
Flutter testing ensures app quality and reliability by validating UI, logic, and performance before deployment.
82. Types of testing in Flutter?
Answer:
-
Unit Testing – Tests individual functions
-
Widget Testing – Tests UI components
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Integration Testing – Tests full app flow
83. What is Unit Testing?
Answer:
Unit testing verifies business logic functions independently using the test package.
84. What is Widget Testing?
Answer:
Widget testing checks UI behavior by rendering widgets in a test environment.
85. What is Integration Testing?
Answer:
Integration testing validates complete app workflows on real or virtual devices.
86. What is Flutter DevTools?
Answer:
Flutter DevTools is a suite of performance and debugging tools for inspecting UI, memory, and CPU usage.
87. What is App Lifecycle in Flutter?
Answer:
Flutter app lifecycle includes:
-
resumed
-
inactive
-
paused
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detached
88. What is WidgetsBindingObserver?
Answer:
WidgetsBindingObserver listens to app lifecycle changes such as background and foreground transitions.
89. How do you secure API keys in Flutter?
Answer:
Use environment variables, .env files, or secure storage instead of hardcoding keys.
90. What is Flutter Secure Storage?
Answer:
Flutter Secure Storage encrypts sensitive data like tokens and passwords using native security mechanisms.
91. What is Code Obfuscation in Flutter?
Answer:
Code obfuscation makes reverse engineering difficult by renaming classes and methods.
92. How do you deploy a Flutter app to Play Store?
Answer:
Generate a signed APK/AAB, create a Play Console account, upload the build, and submit for review.
93. How do you deploy Flutter app to App Store?
Answer:
Build an iOS release using Xcode, upload via App Store Connect, and submit for Apple review.
94. What is CI/CD in Flutter?
Answer:
CI/CD automates testing, building, and deployment using tools like GitHub Actions, Bitrise, or Codemagic.
95. What is Flutter Web?
Answer:
Flutter Web allows building browser-based applications using the same Flutter codebase.
96. What is Flutter Desktop?
Answer:
Flutter Desktop supports Windows, macOS, and Linux app development.
97. What is Tree Shaking in Flutter?
Answer:
Tree shaking removes unused code during compilation to reduce app size.
98. What is Sound Null Safety?
Answer:
Sound null safety guarantees no null errors at runtime through compile-time checks.
99. What is flutter analyze?
Answer:
flutter analyze checks code for errors, warnings, and best practice violations.
100. Why choose Flutter for enterprise apps?
Answer:
Flutter offers high performance, scalability, fast development, single codebase, and strong ecosystem—ideal for enterprise solutions.
