Top 30+ Flutter Interview Questions and Answers for 2024

Top Flutter Interview Questions and Answers

1. What is Flutter?

Flutter is a UI-based tool for creating mobile applications. You can use Flutter to create natively compiled mobile applications with a single programming language and a single codebase. Fast and beautiful mobile applications can be developed with the right skill sets to code in Flutter. Google developed the framework, and the code is open source. Flutter in itself is not a language, and it makes use of Dart language for coding.

Flutter can be used to code for both IOS and Android. The optimization is best suited for 2D mobile apps. The following features can be used to make the apps:-

• Geolocation
• Storage access
• Camera access
• Network
• Third-Party SDKs

2 What are the advantages of using Flutter?

Flutter has various advantages to coding mobile apps:-

1. Reduce the amount of code- Hot reload feature provided by Flutter helps in faster performance. The app is coded in C/C++ code to make it as close to machine code as possible for faster app development. The widget availability in Flutter reduces the time spent on coding and uses reusable code.
2. Cross-Platform development- Flutter code can be used across platforms to reduce the effort on the development team's side.
3. Live and Hot Reloading- It helps write the code faster and more easily. The code can be easily modified when a change is made.
4. Works like a Native app- Flutter code is as close to machine code as possible. This reduces the errors due to the interpretation of code. The app works in a native environment, and the coded apps are fast and easy to use.
5. Community- Flutter has a thriving community to help you with the questions you might have.
6. Minimal Code- The Flutter app is coded using the Dart programming language. This increases the speed of development, and the UI is fast. Dart uses JIT and AOT compilation which is very fast.
7. Faster documentation- It has fast and well-organized documentation. The central depository stores the documents for future reference.
8. Customized designs- The customized layered architecture allows the designing of custom designs, faster rendering and expressive UIs.

3. What is the Flutter architecture?

Flutter has a three-layered architecture:-

• Upper Layer: The upper layer consists of the Dart programming language along with the widgets, animations, illustrations, customizations, etc.
• The middle layer or the Flutter Engine: This layer deals with text display, formatting, layout, etc.
• Bottom Layer or the built-in service: This layer is for managing plugins or packages.

4. What build modes are available in Flutter?

Flutter is made up of three build modes: -

1. Debug Mode- This mode is for debugging apps on a device or a simulator.
2. Profile Mode- Some debugging abilities are available, along with an analysis of app's performance in testing rounds.
3. Release Mode- This mode is used when deploying the app. This mode is for faster performance. You cannot debug or edit the code in this mode.

5. What is the Dart programming language?

Dart is an object-oriented programming language with a syntax like the C Language. The language is open source and was developed by Google in 2011. The language was conceptualized to code the mobile app frontend. The app is used for coding frontend user interfaces. Flutter apps make use of the Dart programming language.

6. Is Dart language necessary for Flutter?

It is compulsory to know the Dart language to use Flutter. Flutter applications make use of the Dart language for coding mobile phone apps.

7. What are widgets in Flutter?

Flutter apps make use of widgets to code mobile phone applications. You will almost exclusively build on Flutter using widgets. Widgets define the view of the app. When you change the code, the widget code is automatically adjusted. Widgets are nested with each other to get the final design of the app. This means the widget is the base on which the app is coded.

8. What are the most useful editors for Flutter apps?

Flutter tools make use of plugins to code mobile phone apps. The plugins can help in Dart code compilation, analysis of the code, and development of apps. Some used Flutter tools for IDE development are

• Visual Studio
• Android Studio
• Xcode
• IntelliJ IDEA
• Eclipse
• Emacs

9. What are packages and plugins in Flutter?

Similar types of classes, interfaces, and sub-packages are known as packages in Flutter or any other object-oriented language. The packages and plugins are used in development to reduce the coder's effort. The coder need not write the code for everything and can use packages and plugins to reduce the coding effort.

The distinction between packages and plugins is minute. Packages are new components or written code in Dart language. Plugins, on the other hand, use native code to allow more functionality. Sometimes the two terms are confused as the same, but a minute distinction exists.

10. Are there any popular apps which make use of Flutter?

There are many popular apps which use Flutter. Some of the apps are:-

• Reflectly
• Google Ads
• Alibaba
• Tencent
• Birch Finance

And many more. The use of Flutter in mobile applications is very high. 

11. What are the Advantages of using Flutter

• Flutter offers flexibility and expressive UI with the faster performance provided by Flutter’s code- Hot reload feature. 
• A wide variety of users can get access and internationalization with the help of Flutter code to web applications.
• Flutter widgets come with native performance on both Android and iOS as flutter code is compiled with ARM machine code using Dart's native compilers.
• Flutter provides faster deployment, customized designs, faster documentation, live and hot coding, and minimal coding with C/C++.

12. Explain the Flutter Architecture

Flutter architecture is made up of three layers.

1. Upper Layer: It has Dart programming language including the widgets, animations, illustrations, customizations, etc. 
2. The middle layer: It is also called the Flutter Engine used for text display, formatting, and layout. 
3. Bottom Layer: It is also called the built-in service and is used to manage the plugins or packages. 

13. What build modes are available in Flutter?

Flutter has 3 build modes, Debug Mode, Profile Mode, and Release Mode. 

14. What is the Dart programming language? Explain in detail.

Features of Dart Programming Language:

• Dart is declarative and programmatic which helps developers to read and visualize the layout very easily in an effortless manner. 
• Dart supports basic programming concepts such as classes, interfaces, and functions as well as the collection that replicates the data structure such as arrays, generics, and optional typing.
• Dart code runs faster several times as compared to JavaScript.
• The Dart virtual machine (VM) uses both Just-in-Time (JIT) and Ahead-of-Time (AOT) compilers to reduce code execution time and offer better performance.
• Dart is very scalable and stable while creating complex applications due to its object-oriented programming interface.

15. What are the limitations of Flutter?

Following are the limitations of a flutter:

• Lack of third-party libraries
• Larger release size 
• Flutter works with Dart language which is not so advanced as C# or C-Sharp and JavaScript.
• Not so user-friendly for iOS developers as it is developed by Google and it takes time to resolve the issues for apple devices. 

16. The most useful editors for Flutter apps

The most useful editors for Flutter apps are Visual Studio, Android Studio, Xcode, IntelliJ IDEA, Eclipse, Vim, and Emacs.

17. What are widgets in Flutter?

Widgets in Flutter are nested with each other to get the final design of the app. Widgets are used to code mobile phone applications.

18. What are the popular apps which make use of Flutter?

19. What are the resources to learn Flutter?

You can learn flutter from Flutter Documentation available as open source on Google. 

20. In What technology is Flutter built?

Flutter is built using C, C++, Skia - 2D rendering engine, and Dart-object-oriented language. 

21. Difference between runApp() and main() in flutter.

main()

• It is a function used to start the program. 
• In Flutter, it is impossible to write any program without the main() function.  

runApp()

• It is used to return the widgets that are connected to the screen as the root of the widget tree to be rendered on the screen. 
• This function is called the main function and is also the driver of the app. 

22. What is the App state?

App State is a shared state or application state. App states can be shared across sections of your app and maintain user sessions in the same way. App state includes activities such as login info, user preferences, E-commerce shopping cart, social networking notifications, etc. 

23. What are packages and plugins in Flutter?

Packages

• It is used as native code in Flutter. 
• It enables more usability of the device.  

Plugins

• It is a new code or components written in the dart programming language.  
• The specific distinctions between the plugins and packages are made only during creating a new package.  

24. What do you mean by keys in flutter?

Keys in flutter are identifiers for widgets, elements, and semantic nodes, whereas GlobalKeys and LocalKeys are the subclasses of Key.

25. Uses of keys in Flutter?

• Keys in flutter are used primarily to preserve the state of modified widgets in the widget trees.
• It is used to reorganize and modify the collections of widgets having equivalent types and defined states.
• It does not modify a tree that consists of only stateless widgets. 

26. What is a container class in a flutter?

A container class in flutter is a widget having the capacity to accommodate multiple child widgets and manage them efficiently through dimensions, padding, and background color.

27. What is Flutter Inspector?

The Flutter Inspector is a powerful tool used to visualize the blueprint of your widgets and their properties in Flutter.

28. Benefits of Flutter Inspector.

• Flutter Inspector can select widget mode in a widget tree. 
• It provides the toggle platform.
• It shows paint baselines and debugs paint.
• It can refresh the widgets as well as show or hide the performance overlay.

29. Different types of streams in Dart

There are two types of streams in Dart, single subscription streams and broadcast streams.  

Single Subscription Streams

• The events within a larger whole are delivered sequentially with single subscription streams. 
• They are used for events that are in received matters or for reading a file. 
• There is only one listener throughout the sequence to trigger the event, else the event won’t be triggered. 

Broadcast Streams

• Initially, the event needs to be subscribed to by the listener, then only these streams deliver events to their subscribers and subscribers can immediately start listening to events.  
• There are several listeners to events simultaneously. Besides, one can also listen to the event again even after canceling a previous subscription.

30. When should you use mainAxisAlignment and crossAxisAlignment?

The crossAxisAlignment and mainAxisAlignment are used to control how a row and column widget aligns with their children depending on our choice. 

mainAxisAlignment

• In mainAxisAlignment, the rows will run horizontally whereas the columns will run vertically.

crossAxisAlignment

• In crossAxisAlignment, The rows will run vertically whereas the columns will run horizontally. 

31. What is the difference between SizedBox and Container?

SizedBox

• The SizedBox widget in Flutter has a specified size. 
• In SizedBox, we cannot set the color or decoration for the widget. 
• We can only use it with a child widget having a specific width or height.

Container

• The Container in Flutter is a parent widget containing multiple child widgets to manage them efficiently in width, height, padding, background color, etc. 
• If we have a widget that needs some background styling may be a color, shape, or size constraint that can be wrapped in a container widget.

32. Differentiate between Hot Restart and Hot Reload?

Hot Restart

• It sets the state value as default by destroying the preserved state value. So if you are using States value in your application then after every hot restart the developer gets a fully compiled application and all the states will be set to their defaults.
• Hot Restart uses completely new typed code to rebuild the app widget tree.
• Hot Restart takes much higher time than Hot reload.

Hod Reload

• It has a combination of the Small r key on the command prompt or Terminal.
• It compiles the newly added code very quickly and sends it to the Dart Virtual Machine. Once the Dart Virtual machine code is updated, the hot reload feature updates the app UI including widgets.  
• Hot Reload will not update the application if it has state values that are preserved by the hot restart feature.

FAQs

1. What is flutter used for?

Flutter is used to create fast, beautiful, natively compiled mobile applications with one programming language and a single codebase.

2. Is Flutter an SDK?

Yes, Flutter is an SDK.

3. How do I prepare for a flutter interview?

To understand the flutter framework thoroughly, one can start with the flutter documentation developed by Google and also available as free in open source form. This will cover your basics and help you understand the ins and outs of the flutter framework. Then you can start going through a list of questions about the flutter to ace your flutter interview.

4. Is Flutter a frontend or backend?

Flutter is a frontend development framework.

Conclusion

These Flutter interview questions can help you crack the interview and get your dream job. Make sure that you not only focus on the Flutter interview questions, but you should improve your knowledge about the subject matter to understand the changing trends and gather more information. You can also check out the Flutter courses to get you started on Flutter development.

If you are looking to expand your career in the mobile app development domain, then do enroll in our Post Graduate Program in Full Stack Web Development Automation Testing Masters which can be a great step in your career.

If you have any doubts or queries, feel free to post them in the comments below and our expert team will get back to you at the earliest.