16/Sep/2024 | 10 minutes to read
mobile-dev
Here is a List of essential Flutter Interview Questions and Answers for Freshers and mid level of Experienced Professionals. All answers for these Flutter questions are explained in a simple and easiest way. These basic, advanced and latest Flutter questions will help you to clear your next Job interview.
These questions are targeted for a Flutter developer. You must know the answers of these frequently asked Flutter technical questions to clear the interview. All these Flutter interview questions and answers are prepared by IT Professionals who have good industry experience.
1. What is flutter?
Flutter is an open-source UI toolkit or software development kit (SDK) developed by Google to build mobile, web and desktop applications from a single codebase. The main component of flutter includes:
2. What are the advantages of using Flutter?
Flutter comes with many advantages as:
3. What are the limitations of Flutter?
Flutter has certain limitations as:
4. Who developed the flutter framework?
Flutter Framework is developed by Google.
5. What are the resources to learn Flutter?
You can refer Flutter Documentation to learn flutter.
6. What type of applications can you develop using Flutter?
Flutter is an open-source UI toolkit by Google to develop android, iOS, Linux, Mac and Web applications from a single codebase. Flutter is a good choice for apps which needs to deliver high brand designs.
7. Is Flutter Open source?
Yes, Flutter is a free and open-source UI toolkit by Google to develop desktop, web and mobile applications with one codebase only.
8. What makes Flutter unique?
Flutter uses only a single codebase to develop applications for web, mobile and desktop and the experience for mobile apps is native on both android and iOS. Flutter does not depend on web browser technology nor the set of widgets that each device contains. Instead it uses its own rendering engine to draw widgets. This rendering engine provides very high performance. This concept makes flutter unique.
9. Explain Flutter SDK.
Flutter SDK is an UI kit to build applications for mobile, web and desktop from a single codebase. This SDK comes with a flutter command line tool and dart command line tool to develop apps across platforms. For more you can refer Flutter SDK.
10. What do you understand from hot reload and hot restart?
Hot reload means injecting the updated source code files into running Dart VM (Virtual Machine). Hot reload process does not add
only new classes but it also adds properties, fields and methods to existing classes, and changes existing functions.
Hot restart works by resetting the app's current state to the app's initial state.
For more you can visit Hot reload.
11. How does Flutter run the code on Android?
Android's NDK compiles the flutter engine's C,C++ code. The AOT (ahead-of-time) compiler compiles the Dart
code of both (SDK's and your) into native, ARM, and x86 libraries. These libraries are added in a "runner" android project and the whole thing or artefact is
built into an Android application package file .apk. The app loads the flutter library on launching of it. Any input or event handling, rendering and so on, are delegated
to the compiled code of flutter and app. It is similar to working process of many game engines.
During debug mode, A VM (Virtual Machine) runs flutter code in order to enable hot stateful reload feature. When you run app in debug mode you will see a "debug" banner
in top right corner of app. It reminds you that performance is not the characteristic of completed release app.
12. How does Flutter run the code on iOS?
The Flutter Engine's C, C++ code is compiled with LLVM (low level virtual machine - a compiling technology). The Dart code of both the SDK's and yours are
compiled by AOT (ahead-of-time) into a native, ARM library. That ARM library is included in "runner" iOS project and the whole code base is built into an
iOS App Store Package file .ipa. When the app launched, the app loads the flutter library. Any input or event handling, rendering and so on, are delegated
to the compiled code of flutter and app. It is similar to working process of many game engines.
Debug mode works same as for Android app.
13. In What technology is Flutter built?
Flutter is built using C, C++, Skia - 2D rendering engine and Dart (a modern, concise, object-oriented language). For you can visit Flutter System Architecture and Flutter architectural overview.
14. What is the use of the pubspec.yaml file?
When you create a new Flutter project, It includes a pubspec.yaml file also known as 'pubspec' at the top of the project tree. IT contains metadata
about the project that is required by Dart and Flutter tooling. It is written in YAML and human readable.
The pubspec file contains the dependency information that project requires like packages and their versions, fonts etc. It ensures that you get the same package version
the next time when you build the project. For more visit pubspec.
15. Explain stateful widgets and stateless widgets in flutter?
Radio, Checkbox, slider are examples of
stateful widgets.
IconButton, Icon, Text etc.16. What do you understand from 'State'? What is the use of the setState() method?
State refers to the information that you can read synchronously when a widget is built and it might change during the lifetime of the widget.
The widget implementor should ensure that the 'State' is promptly notified on change of state using State.setState method. The 'setState' method
is used to notify the changed state of an internal object.
17. What operating systems flutter support to build the apps?
Flutter app development can be done using Linux, MacOS, ChromeOS and Windows.
18. What is a Cookbook?
The Cookbook provides solutions or recipes for common occurring problems while developing flutter apps. Each recipe is an independent complete solution and can be referenced to help you build up an app. For more you can refer Cookbook.
19. What is the Container class in flutter?
The Container class provides the ability to create a widget with certain properties like padding, borders, height, width, border etc.
20. How will you make a HTTP request in flutter?
21. Can a container have more than one child?
22. What is SafeArea in flutter?
23. How JSON Serialization works in flutter?
24. How to Parse JSON in flutter?
25. What resources are available to learn flutter?
For Flutter tutorials visit Flutter Tutorials
State Management Techniques:
26. Elaborate on the different state management techniques in Flutter, highlighting their strengths and weaknesses.
Flutter provides various state management techniques, each with its own strengths and weaknesses. setState is suitable for simple, localized state management, but can become cumbersome and error-prone as complexity grows. The BLoC (Business Logic Component) pattern and Provider package are more robust solutions for managing complex state across multiple widgets and screens.
27. Explain when you would choose to use a more robust solution like the BLoC pattern or Provider over the simple setState approach.
The BLoC pattern promotes separation of concerns and reactive programming, making it easier to manage and test state. It involves creating separate Blocs for different features, each managing its own state and emitting events that widgets can listen to and react accordingly. This approach fosters code reusability, testability, and maintainability.
28. How you would implement a complex state management scenario using your preferred technique.
For complex state management scenarios, I would opt for the BLoC pattern or a modern state management solution like Riverpod. With BLoC, I would create distinct Blocs for each feature, encapsulating their respective state management logic and exposing streams that widgets can subscribe to. With Riverpod, I would create reusable and testable state notifiers that can be easily consumed by widgets throughout the app.
Flutter Architecture and Project Structure:
29. Describe the architecture of a typical Flutter app, explaining the role of different components such as Widgets, State, Streams, and Providers.
A typical Flutter app follows a widget-centric architecture, where the user interface is composed of reusable and composable widgets. The app's state is managed separately using techniques like setState, BLoC pattern, or Provider. Streams are used for asynchronous data flow and reactive programming, enabling widgets to react and update their UI accordingly.
30. Discuss how you would structure a large-scale Flutter project to ensure maintainability and scalability
For large-scale Flutter projects, I would follow a modular architecture, where each feature or domain is encapsulated in its own module. Each module would contain its respective widgets, state management logic, data models, repositories, and services. This approach promotes code reusability, testability, and maintainability, as well as facilitates collaboration among team members working on different features.
31. Explain the concept of Flutter Plugins and when you would create a custom plugin.
Flutter Plugins are packages that integrate platform-specific code (Android/iOS) into Flutter apps, allowing access to native device features or APIs that are not available in the Flutter framework. I would create a custom plugin when I need to leverage native device capabilities or integrate third-party SDKs that require platform-specific implementations, such as accessing device sensors, implementing advanced media playback functionality, or integrating a third-party payment gateway SDK.
Performance Optimization:
32. Discuss the techniques you would employ to optimize the performance of a Flutter app, focusing specifically on handling large lists or grids with smooth scrolling.
To optimize a Flutter app's performance, I would employ a combination of techniques, including code splitting, widget rendering optimization, and efficient data loading strategies.
For handling large lists or grids while ensuring smooth scrolling, I would leverage Flutter's built-in ListView.builder or GridView.builder widgets. These widgets render items lazily as the user scrolls, minimizing the initial rendering overhead and improving scrolling performance. Additionally, I would implement techniques like list view recycling and efficient diffing algorithms to minimize redundant widget rebuilds.
33. Explain the concept of lazy loading and how you would implement it in a Flutter app to enhance performance and user experience.
Lazy loading involves loading resources (e.g., images, data) only when they are needed, rather than loading everything upfront. This approach can significantly improve initial load times and reduce memory consumption. To implement lazy loading, I would employ strategies like pagination or infinite scrolling, fetching and rendering additional data as the user scrolls towards the end of the currently loaded data.
Widget Lifecycle and Rendering:
34. Explain the flutter widgets.
Flutter Widgets can be defined as an immutable description of a part of the UI. Each element on the flutter app's screen is considered as a widget. In flutter, the UI is built using widgets. There is no mutable state associated with a widget, you can use flutter stateful widget to associate a mutable state with a widget. For more about a widget class refer Widget class.
35. Explain the widget lifecycle in Flutter, highlighting the different callback methods and their purposes.
The widget lifecycle in Flutter consists of various callback methods that allow developers to perform specific actions or execute logic at crucial points during the widget's existence. Methods like initState, didChangeDependencies, build, didUpdateWidget, and dispose are used for tasks such as initializing state, reacting to dependency changes, rendering the UI, handling updates, and cleaning up resources.
36. Describe how Flutter handles rendering and discuss techniques you would use to optimize rendering performance, including the concept of keys and their importance in rendering.
Flutter's rendering pipeline is optimized for performance. It uses a retained mode rendering approach, where the widget tree is constructed and diffed against the previous tree, and only the necessary updates are applied to the render tree. To optimize rendering performance, techniques like judicious use of keys, avoiding unnecessary rebuilds, and leveraging immutable data structures are employed.
Keys in Flutter are used to preserve the state of a widget across rebuilds. By providing a unique key to a widget, Flutter can identify and reuse the existing widget instance instead of creating a new one, improving performance and preserving state. Keys are particularly useful in scenarios like lists or grids, where individual items can be reordered or removed without affecting the entire list.
Testing and Continuous Integration:
37. Discuss your approach to testing in a Flutter app, including the different types of tests (unit, widget, integration) and the tools and frameworks you would use.
Testing in a Flutter app involves unit tests for testing individual functions or classes, widget tests for testing the UI and widget behavior, and integration tests for testing end-to-end scenarios.
For testing Flutter apps, I would use the built-in testing frameworks provided by Flutter, such as test for unit tests and flutter_test for widget and integration tests. Additionally, I might use third-party frameworks like Mockito for mocking dependencies and Golden for visual regression testing.
38. Explain the importance of Continuous Integration (CI) and Continuous Deployment (CD) in Flutter app development, and how you would set up a CI/CD pipeline.
Continuous Integration (CI) and Continuous Deployment (CD) are essential for ensuring the quality and reliability of a Flutter app. I would set up a CI pipeline using tools like GitHub Actions, CircleCI, or Jenkins to automatically build, test, and deploy the app with every code change. The CI pipeline would handle tasks like running automated tests, building release artifacts, and deploying the app to various distribution channels like app stores or web hosts. CD would enable seamless deployment of new versions to production environments.
Flutter Web and Desktop:
39. Explain the differences between developing for mobile, web, and desktop platforms in Flutter.
While Flutter provides a unified codebase for developing apps across multiple platforms, there are some differences and considerations when targeting mobile, web, and desktop platforms. On mobile platforms (iOS and Android), Flutter apps have access to a wide range of native device features, such as sensors, cameras, and platform-specific APIs. The user experience is optimized for touch interactions, and performance considerations are critical due to the limited hardware resources of mobile devices.
40. How would you handle platform-specific code and functionality in a Flutter app targeting multiple platforms?
To handle platform-specific code and functionality in a Flutter app targeting multiple platforms, I would employ techniques such as conditional imports, platform checks, and Flutter's built-in platform APIs. For example, I might use kIsWeb or Platform.isAndroid to execute platform-specific code or load different UI components based on the target platform.
41. Describe the limitations and challenges of developing for Flutter Web or Desktop platforms.
Flutter Web apps run within a web browser environment and are subject to the constraints and limitations of web technologies. They have limited access to native device features and may face performance challenges for certain use cases, such as graphics-intensive applications or demanding computations.
Advanced Flutter Concepts:
42. Explain the concept of Flutter Hooks and when you would use them.
Flutter Hooks are a way to introduce stateful logic into functional components, allowing for easier code reuse and better separation of concerns. Hooks provide a mechanism to encapsulate and share stateful logic across multiple components, promoting code reusability and maintainability. I would use Hooks when I need to encapsulate complex stateful logic or share state between multiple components, such as managing a form state or subscribing to a stream of data.
43. How would you implement a custom animation in Flutter?
To implement a custom animation in Flutter, I would leverage the Animation and AnimationController classes. The AnimationController manages the animation's lifecycle and provides methods to start, stop, and control the animation's progress. I would define the animation curve, which determines the animation's timing and interpolation, and tween values, which represent the start and end states of the animation. Then, I would update the widget's state based on the animation's value changes, using the build method to render the animated UI.
44. Describe the difference between StatefulWidget and StatelessWidget, and when to use each.
In Flutter, StatefulWidget and StatelessWidget are two different types of widgets that handle state management differently. StatefulWidget is used when a widget needs to maintain its own mutable state and is responsible for creating a State object that holds the widget's state and provides methods to update and manage that state. StatelessWidget, on the other hand, is used for widgets that simply render based on the provided configuration or props and do not have any internal state.
45. Explain the lifecycle of a StatefulWidget?
Architecture Patterns and Design Principles:
46. What architecture patterns or design principles would you follow when developing a Flutter app?
When developing Flutter apps, I follow the Model-View-ViewModel (MVVM) or Clean Architecture patterns. These patterns promote separation of concerns, testability, and maintainability, making it easier to develop, maintain, and scale complex applications.
The MVVM pattern separates the application into three main components: the Model (data and business logic), the View (UI components), and the ViewModel (mediator between the View and Model). This separation allows for better code organization, testability, and reusability, as well as facilitates the implementation of reactive programming paradigms.
47. How would you implement dependency injection in a Flutter app?
For implementing dependency injection in a Flutter app, I would use a package like get_it or injectable. Dependency injection promotes loose coupling, testability, and maintainability by allowing dependencies to be injected into classes or modules, rather than being hard-coded. This simplifies the management of shared dependencies across the application, reducing code duplication and improving code organization.
48. Explain the importance of separation of concerns and how you would apply it in a Flutter project.
Separation of concerns is a crucial principle for building maintainable and scalable applications. In a Flutter project, I would separate the app's functionality into distinct layers or modules, each responsible for a specific concern (e.g., UI, business logic, data access, networking).
Flutter Plugins and Integration:
49. How would you integrate native platform code (Android/iOS) into a Flutter app using platform channels?
To integrate native platform code (Android/iOS) into a Flutter app, I would use platform channels. Platform channels allow bidirectional communication between the Flutter app and the native platform code, enabling access to platform-specific APIs or features that are not available in the Flutter framework.
The process of integrating native code involves creating a platform-specific implementation (e.g., Java/Kotlin for Android, Objective-C/Swift for iOS) that exposes the desired functionality. This implementation communicates with the Flutter app through a messaging protocol, where data is passed back and forth using method calls and event streams.
On the Flutter side, I would create a platform interface that defines the API for interacting with the native code. This interface acts as a bridge between the Flutter app and the platform-specific implementations, providing a unified Dart API for seamless integration.
50. Explain the process of creating and publishing a custom Flutter plugin.
Creating and publishing a custom Flutter plugin involves several steps: setting up the plugin project structure following the Flutter plugin template, implementing the platform-specific code, creating a platform interface, writing tests to ensure the plugin's functionality, and finally publishing the plugin to a package repository like pub.dev for others to use.
51. Describe your experience with integrating third-party libraries or SDKs into a Flutter app.
I have experience integrating third-party libraries and SDKs into Flutter apps, such as Firebase services like Authentication, Firestore, and Cloud Messaging. The process involves following the official documentation, creating platform-specific implementations, and exposing a unified Dart API for seamless integration within the Flutter app.
Flutter Community and Best Practices:
52. How do you stay updated with the latest Flutter developments, releases, and best practices? What resources or communities do you follow for learning and sharing knowledge about Flutter? Explain some of the best practices you follow when developing Flutter apps.
Stay updated through official Flutter documentation, events, meetups, and online communities like subreddits, Discord channels, and Twitter. Follow resources like Flutter weekly newsletter, Google's Flutter blog, and publications like The Flutter Way. Follow best practices like adhering to the Flutter style guide, writing modular and testable code, optimizing performance, and leveraging accessibility features.
Where can you find answer of Dart interview questions?
For Dart Interview questions, we have a separate document here Dart Interview Questions
1. How much will you rate yourself in Flutter?
When you attend an interview, Interviewer may ask you to rate yourself in a specific Technology like Flutter, So It's depend on your knowledge and work experience in Flutter. The interviewer expects a realistic self-evaluation aligned with your qualifications.
2. What challenges did you face while working on Flutter?
The challenges faced while working on Flutter projects are highly dependent on one's specific work experience and the technology involved. You should explain any relevant challenges you encountered related to Flutter during your previous projects.
3. What was your role in the last Project related to Flutter?
This question is commonly asked in interviews to understand your specific responsibilities and the functionalities you implemented using Flutter in your previous projects. Your answer should highlight your role, the tasks you were assigned, and the Flutter features or techniques you utilized to accomplish those tasks.
4. How much experience do you have in Flutter?
Here you can tell about your overall work experience on Flutter.
5. Have you done any Flutter Certification or Training?
Whether a candidate has completed any Flutter certification or training is optional. While certifications and training are not essential requirements, they can be advantageous to have.
We have covered some frequently asked Flutter Interview Questions and Answers to help you for your Interview. All these Essential Flutter Interview Questions are targeted for mid level of experienced Professionals and freshers.
While attending any Flutter Interview if you face any difficulty to answer any question please write to us at info@qfles.com. Our IT Expert team will find the best answer and will update on the portal. In case we find any new Flutter questions, we will update the same here.