Flutter is a revolutionary framework for creating cross-platform apps that are gaining traction in the mobile market as the next big thing. From small to large organizations understand the benefits of combining two or three teams into one common code base. Flutter developer jobs are becoming more plentiful in the current tech market. 

So, you'll go over a number of Flutter interview questions and answers in this article. Work through each of the questions below if you're a developer looking for a new job. Our team divided Top 35 Flutter Interview Questions and Answers into the following sections for freshers, intermediate and experienced candidates. Before you look at the answer, try to come up with a solution on your own. This might assist you in identifying areas where you can improve your abilities.

Top Flutter Interview Questions and Answers

• Flutter Interview Questions and Answers for Freshers
• Flutter Interview Questions and Answers for Intermediate candidates
• Flutter Interview Questions and Answers for Experienced candidates

Flutter Interview Questions and Answers for Freshers

1. What is Flutter?

Flutter is a UI toolkit that allows you to create fast, compiled web, desktop, and mobile applications using a single programming language and codebase. It is a Google-created open-source development framework. 

Flutter, in general, is not a language; it is an SDK. Dart programming language is used to develop Flutter apps. Flutter's first alpha version was available in May 2017.

Flutter is intended for 2D mobile apps that run on iOS and Android platforms. We can also use it to create full-featured applications with a camera, network, geolocation, third-party SDKs, storage, and many other features.

2. What is Dart?

Dart is an object-oriented programming language with C-style syntax. It is open-source and was created in 2011 by Google. Dart programming creates front-end user interfaces for mobile and web apps. It is an essential language for developing Flutter apps. The Dart programming language can be compiled into JIT (Just-in-Time) or AOT (Ahead-of-Time).

3. How can you perform asynchronous operations in Dart?

A method can return the Future type from an asynchronous action. We can use the await keyword to retrieve the desired result by adding the async keyword to the method definition. If Dart employs async-await keywords, then the callback is used to resolve a Feature.

4. Explain the term const in Flutter?

The keyword const is used to declare constants. The values of variables declared with const cannot be changed. The keyword represents a compile-time constant. During compilation, it produces an item and inserts it whenever the same object is needed.

5. Explain about Flutter Widgets?

Flutter Widgets are an immutable description of a part of the user interface. Every element on the flutter app's screen is referred to as a widget. The UI in Flutter is built with widgets. They provide information about the views, such as their configuration and state. There is no mutable state associated with a widget; however, you can associate a mutable state with a widget by using the flutter stateful widget. To be displayed on the screen, the widgets are displayed in a hierarchical order. Text, scroll, checkboxes, buttons, images, and other UI components in Flutter are widgets.

6. Explain what you understand in Stateless and Stateful widgets in Flutter?

Stateless: A widget state is created ONLY ONCE, after which it can only update values and not the state explicitly. As a result, stateless widgets are immutable, and there is only one class that extends StatelessWidget. They will never be able to re-run the build() method again.

Stateful: When an event occurs, widgets can update their STATE (locally) and values multiple times. As a result, Stateful widgets also seem to be immutable. Because of this, the implementation is also distinct, but it is coupled with a State object that allows you to rebuild the Widget with new values whenever setState is called (). When the UI can change dynamically, StatefulWidget is used. Assume that the state becomes more complex or that the same state appears in two different widgets. In that case, you should consider two classes: StatefulWidget and its State implementation handler, StateYourWidget>. As a result, it can re-run the build() method based on the events.

7. Explain various types of editors for Flutter development?

IDEs (interactive development environments) are software programs that allow users to create and edit text files. Editors are commonly used in the development field to refer to source code editors, including many unique features for writing and editing code.

We can build Flutter apps with any text editor that works well with our command-line tools. However, for a better experience, editor plugins (IDE) are recommended. These plugins include syntax highlighting, code completion, widget editing assistance, run & debug support, and various other features. Flutter supports a variety of IDEs for app development. Some of them are discussed below, but you can use a different editor if you prefer. Here are a few Flutter editors:

• Android Studio: It speeds up development and creates high-quality apps for all Android devices. It enables the developer to fix code issues automatically. It also offers a complete development experience for Flutter apps, such as widget editing assistance, code completion, syntax highlighting, navigation, refactoring, run and & debug functionality, and so on.
• IntelliJ IDEA: JetBrains also designed and maintains the most advanced IDE in the developer community. The Apache 2.0 license governs its use. It enables you to construct apps in a variety of languages. It will quickly become a popular IDE for many developers because it supports outstanding plugins and has a wide built-in feature set. Creating the apps with the Dart language is an obvious winner when compared to other IDEs. It includes smart coding aid for Dart, such as code completion, formatting, navigation, intents, refactoring, a built-in debugger, pub integration, and the Dart Analysis Server, as well as a built-in debugger.
• Visual Studio Code: The Visual Studio Code IDE is a well-known editor for writing Flutter apps. It is both free and easy to use. Because Microsoft supports this IDE, most developers use it to create Flutter apps. It comes with a basic Dart plugin that makes app development go faster. It includes syntax highlighting, the Pub Upgrade Packages command, code completion, the Pub Get Packages command, type hierarchy, and more. The Visual Studio code editor is available for Linux, Windows, and macOS.
• Codemagic: It is also used to develop, test, and deploy Flutter applications quickly. The creation of an app can be speeded significantly by using the Flutter framework. Cinemagic can use it to test and publish the app. It also makes it easier to promote our app without causing too many issues. It's a completely open-source and free IDE. It also allows us to submit anything we want to aid in the documentation's improvement.

8. Tell us about Flutter plugins and packages?

A package is a collection of similar interfaces, classes, and sub-packages. Packages and plugins allow us to build the app without writing everything from scratch. It is possible to import new functionality or widgets into the Flutter app. There is only a minor distinction between plugins and packages. In general, packages are new components or code written in dart languages, whereas plugins provide additional features on the device by utilizing native code. Plugins and packages are both referred to as packages in the DartPub.

9. What are the advantages of Flutter?

Here are a few Advantages of Flutter: 

• Cross-platform Development: With this feature, Flutter can write code once, maintain it, and run it on multiple platforms. It saves developers time, effort, and money.
• Faster Development: The Flutter application performs well and compiles the application using the arm C/C++ library, which brings it closer to machine code and improves native performance.
• Good Community: Flutter has good community support where developers can ask questions and get answers quickly. It speeds up the app development process by allowing live and hot reloading. This feature will enable us to change or update the code, and the changes are reflected as soon as they are made.
• Live and Hot Reloading: It speeds up the app development process by allowing live and hot reloading. This feature will enable us to change or update the code, and the changes are reflected as soon as they are made.
• Minimal code: Dart programming language is used to create the flutter app, which uses JIT and AOT compilation to improve overall commencement, functionality, and performance. JIT improves the development model and refreshes the UI without requiring additional effort to create a new one. It has an excellent user interface due to a design-centric widget, high-development tools, advanced APIs, and many other features.
• Documentation: Flutter provides excellent documentation. It is more organized and informative. We can get everything we need to be written down in one place.
• Native Performance: Dart compilers perform an essential role in compiling your flutter code because it is compiled into native ARM machine code using Dart's native compilers. Flutter widgets perform natively on both iOS and Android.
• Flutter offers accessibility and internationalization to a wide range of users worldwide.

10. Explain about the Android and IOS folder in the Flutter project?

Android: A full Android project is contained in this folder. When creating Flutter Android applications, it is used. When the Flutter development is finished, it is injected into this Android project, producing a native Android app. When using the Android operating system, for example, this Android project is used to create an Android app, which is subsequently published to an Android Virtual Device.

iOS: This folder provides a complete Mac project for iOS. When creating Flutter apps for iOS, it is essential. It's similar to the Android folder in which an Android app is created. When Flutter code is converted to native code, it is injected into this iOS project, resulting in a native iOS app. Only macOS and the Xcode IDE may be used to create a Flutter app for iOS.

11. What are the disadvantages of Flutter?

Flutter has the following limitations: 

• Lack of third-party libraries-Flutter has a small number of third-party repositories, but this is growing over time.
• A larger release size-Flutter disappoints developers when the closure size does not meet their expectations.
• Dart is an excellent object-oriented programming language, but it falls short when compared to others such as C# (C-Sharp), JavaScript, and others.
• Development teams often think twice before using the flutter structure to develop an app for Apple devices because Google develops it. The challenges for Android devices are resolved quickly, but Apple devices' issues take a long time.

12. How does flutter run the code on Android?

The NDK for Android compiles the C and C++ code of the flutter engine. The AOT (ahead-of-time) compiler compiles both (SDK's and you're) Dart code into native, ARM, and x86 libraries. These libraries are added to an Android "runner" project, and the entire thing or artifact is built into an Android application package file.apk. When you launch the app, it loads the flutter library. Any input or event handling, rendering, and so on are delegated to flutter, and the app's compiled code. It is similar to how many game engines work.

A VM (Virtual Machine) runs flutter code in debug mode to enable the hot stateful reload feature. A "debug" banner will appear in the top right corner when you run the app in debug mode. It serves to remind us that performance is not a feature of a finished release app.

Flutter Interview Questions and Answers for Intermediate Candidates

13. How does flutter run the code on IOS?

LLVM is used to compile the C and C++ code in the Flutter Engine (low-level virtual machine - a compiling technology). The SDK's and your Dart code are AOT (ahead-of-time) compiled into a native ARM library. That ARM folder is included in the "runner" iOS project, and the entire code base is packaged as an iOS App Store Package file. ipa. The flutter folder is loaded when the app is launched. Any input or event handling, rendering, and so on are outsourced to flutter and the app's compiled code. It is similar to how many game systems work. Debug mode functions similarly to that of an Android app.

14. List out a few apps that are using Flutter

Google's Flutter is an open-source UI toolkit that allows you to create Mac, iOS, Android, Linux, and Web applications from a single code. Flutter is an excellent choice for apps that require high-quality branding. So many organizations started using Flutter to build their apps. Following are a few apps built on Flutter: 

• Google Ads
• Reflectly
• Alibaba
• Birch Finance
• Coach Yourself
• Tencent
• Watermaniac

15. Explain about Hot Reload and Hot Restart in Flutter

Hot Reload: The Flutter hot reload feature is activated by pressing the Small r key on the command window or Terminal. The hot reload feature compiles the newly added code in our file and sends it to the Dart Virtual Machine. After you've finished updating the Code Dart Virtual Machine, you should update the app's UI with widgets. Hot reloading is faster than hot restarting. There is also a disadvantage to Hot Reload. If you use States in your application, Hot Reload preserves the States, so they will not upgrade on Hot Reload unless they are set to their default parameters.

Hot Restart: Hot restart is not the same as hot reload. When you perform a hot restart, it destroys the preserves State value and resets it to its default. So, if you use the States value in your app, the developer will receive a fully executable application with all states set to their defaults after each hot restart. The app widget tree has been fully restored with new code. Hot Restart takes significantly longer than Hot Reload.

16. What is the difference between main() and runApp() functions in Flutter?

The difference between main() and runApp() is as stated below: 

• The main() function is in command of initiating the program. We can't write a Flutter code without the main() function.
• The runApp() function is in command of restoring the widgets associated with the screen and will be delivered on the screen as the root of the widget tree.

17. When to use mainAxisAlignment and  crossAxisAlignment in the Flutter?

We can use the crossAxisAlignment and mainAxisAlignment properties to control how row and column widgets align their tree/roots. The mainAxisAlignment property specifies how items are aligned on the main axis, horizontal in a row and vertical in a column. The following image helps you to understand easily.

The property crossAxisAlignment specifies how elements are aligned along the other axis (vertical in a row, horizontal in a column).

18. Describe various types of Streams in Flutter?

• The Future and Stream classes in Dart define asynchronous programming.
• A stream is an asynchronous sequence of events. It is similar to an asynchronous Iterable in that, instead of returning the next event when requested, the stream informs you that an event will be returned when it is ready.
• Streams can be created in various ways, but they all serve the same purpose: the asynchronous for loop ( await for). Eg

  Future sumStream(Stream stream) async {   var sum = 0;   await for (var value in stream) {     sum += value;   }   return sum;

   

• Streams provide an asynchronous data sequence.
• User-generated events and data read from files are examples of data sequences.
• The Stream API's await and listen() methods can process a stream.
• Streams allow you to respond to errors.
• The following are two kinds of Streams in Flutter:

1. Single subscription Streams: It comprises a series of events that form part of a larger whole. Events must be delivered in the correct order, without any gaps. - When you read a file or receive a web request, you get this stream type. - A stream like this can only be listened to once. Listening later may result in missing out on the initial events, after which the rest of the stream becomes meaningless. - When you begin listening, data will be fetched and delivered in chunks.
2. Broadcast Streams: 

• It is designed for single messages that can be handled one at a time. This type of stream, for instance, can be used for mouse events in a search engine.
• You can begin listening to such a stream at any time, and you will receive the events that occur while you are listening.
• Multiple listeners can listen simultaneously, and you can listen again after canceling a previous subscription.

19. Tell us the reason why the build() method on State not Stateful widgets?

Because all fields within a widget, including its subclasses, are immutable, statefulwidget requires a different state class that does not have a build method within its body.

You may have noticed that statelesswidget has its build and other associated methods described within it, but this was possible due to the nature of statlesswidget, which is rendered entirely using the provided information and does not anticipate any future changes in its State.

State information changes (or is expected to change) during the app in the case of StatefulWudget; thus, this information isn't suitable for storage in a final field (build) to satisfy Widget class conditions (all fields are immutable). That is why the State class was created. To attach your defined State to your StatefulWidget, you must override the create state function and keep all changes in a separate class.

20. Explain stateful widget lifecycle methods?

• Create State () — This function creates a State object. The mounted attribute is set to true once the State is formed. This guarantees that the widget is now located within a widget tree.
• initState() – This function is called after a widget is added into a tree and before State's constructor. When the state is generated, it is only called once.
• didChangeDependencies() – When a dependence of this State object changes, this method is called. Because the build() function will be contacted soon after this method, it is rarely utilized. It is, however, extremely effective when used in conjunction with for InheritedWidget
• build() – This method is used to create our widget tree. It keeps track of all the widgets and arranges them on the screen. Throughout the widget's existence, it will be called multiple times.
• didUpdateWidget() – When the parent widget updates and the current widget needs to be restored, this method. You are given an old widget to compare to the new one as input.
• deactivate() — This function is invoked when a widget is removed from a widget tree.
• dispose() —-When State is removed permanently from the widget tree. The mounted attribute is then set to false.

21. What is the use of Ticker in Flutter?

In Flutter, a ticker represents the rate at which our animation is refreshed. It is a signal-sending class that sends a signal at regular intervals, i.e., approximately 60 times per second. We can figure it out by looking at our watch, which ticks at regular intervals. Ticker includes a callback method that returns the duration of each tick since the first tick at each second after it was started. Even if the tickers began at different times, they always synced independently.

22. Explain about various keys in flutter and when to use the keys?

Keys are parameters that control which widgets match up with other widgets when the widget rebuilds and preserve widget states when moved in a widget tree. A key is used to identify SemanticsNodes, Widgets, and Elements. A new widget will only update a current element if its key is the same. Keys must be distinct among Elements with the same parent. Key subclasses should either be LocalKey or GlobalKey. When manipulating collections of widgets of the same type, keys come in handy. If you need to add, remove, or reorder a group of widgets of the same type that hold some state, you should use a key.

23. Explain about Flutter tree shaking?

The dart2js compiler generates the JavaScript bundle when compiling a Flutter web application. A release build has the most significant optimization standard, which includes tree-shaking your code. Tree shaking completely removes dead code by including only code executed. This means you don't have to be concerned with the state of your app's included archives because unused classes or functions are removed from the executable JavaScript bundle.

24. What is the use of navigators and routers in Flutter?

Navigation and routing are key principles in all mobile apps, letting users switch between pages. We all know that every mobile application has multiple screens for displaying various types of information. An app, for example, could have a screen with a variety of products. When the user taps on that product, detailed information is displayed immediately.

Flutter Interview Questions and Answers for Experienced candidates

25. Explain about Global keys?

GlobalKeys allow widgets to move parents without losing state anywhere in your app, or they can be used to acquire information about the other widget in a specific region of the widget tree. You'd use a GlobalKey in the first instance if you wanted to demonstrate the same widget on two distinct screens while keeping them all in the same state.

26. State the differences between materialApp and widgetApp?

materialApp	widgetAPP
MaterialApp is a layer constructed on top of WidgetsApp and its library, together with the material library. It uses Material Design to provide our app with a consistent look and feel across all platforms.	For primary navigation, WidgetsApp is used. It contains several core widgets and the widgets library that Flutter uses to build our app's UI.
It includes various useful tools for designing applications, such as Navigator and Theme.	The MaterialApp class inherits from the WidgetsApp class.
It encapsulates several widgets that are essential for material design applications.	It encapsulates several widgets that are essential for the application's development.

27. State various tests that you can perform in Flutter?

Testing is a process used to ensure that software or application is bug-free and fulfills the user's needs. Testing is an essential phase in the development lifecycle for providing high quality. It is the most time-consuming phase of app or software development.

The Flutter framework is an excellent tool for automating application testing. To test an application, automated testing is divided into three types. These are their names:

• Unit Testing: It is the simplest way to test an application or software. It only puts a single function, method, or class to the test. Unit testing seeks to ensure that code is proper under various conditions. Unit testing, in general, does not communicate with user input, does not render on the screen, does not read or write data from the disk, and does not use inter-dependencies by default. External dependencies are mocked out with packages like Mockito when they are used.
• Widget Testing: Widget testing is a technique for evaluating a single widget. The goal of this test is to confirm that the widget's UI looks and communicates with other widgets in the way that it should. The technique of widget testing is comparable to that of unit testing, although it is more thorough. This testing entails numerous classes and necessitates the use of a test environment in order to uncover more flaws. A widget that is being tested is capable of receiving and responding to user events and actions, as well as instantiating child widgets.
• Integration Testing: The above testing and the app's external components are included in an integration test. It verifies the entire app or a significant portion of it. Integration testing is used to confirm that all widgets and functions operate together as planned. It can also be used to test the app's functionality. Integration testing is typically performed on genuine devices, such as iOS or Android simulators.

Flutter also offers a golden test, a type of additional testing. Its objective is to make sure you have a picture of a widget or screen and see if the actual widget matches it.

28. Explain about Context in Flutter?

The widget's context is a handle to its position in the widget tree. It's a BuildContext instance that the widget builder uses to figure out where it is in the widget tree. It's simply a reference to a Widget's position within the tree structure of all the constructed widgets.

29. Describe Spacer in Flutter?

To build a flexible space, the Spacer class is used. With the flex container, this space maintains the distance between both widgets. The constructor of the Spacer uses flex to determine the space.

30. Explain about ScopedModel and BLoC pattern in Flutter?

ScopedModel and BLoC (Business Logic Components) are two popular Flutter app development patterns for separating application logic from UI code and reducing the number of Stateful Widgets.

Scoped Model is a standalone component that is not part of the Flutter framework. It's a set of tools that make it simple to pass a Data Model from a parent Widget to its offspring. In addition, when the model is updated, it rebuilds all of the children who use it. This module was derived from the Fuchsia source code.

Business Logic Components (BLoC) is an acronym for Business Logic Components. It allows us to manage your project's state and data from a single location. Almost everything in the app should be displayed as a stream of events, with widgets submitting events and other widgets responding. The discussion is managed by BLoC, which sits in the middle.

31. List out various modes that can be used in the Flutter development?

Following are the various modes that can be used in the Flutter development: 

• Debug mode, which supports Hot Reload, is primarily utilized during development.
• Profile mode is used to analyze the performance of the application. 
• Release mode is used to optimize an app and reduce the size of its footprint, and in this phase, it deploys the application.

32. Explain Debug mode and when to use it in Flutter?

A VM (Virtual Machine) runs flutter code during debug mode to provide a hot stateful reload functionality. A "debug" banner will appear in the top right corner when you start the program in debug mode. It serves as a reminder that efficiency is not a defining feature of a finished app.

33. Explain about profile mode and when to use it in Flutter?

• Some debugging capability is preserved in profile mode—enough to profile your app's functionality.
• When you wish to analyze performance, you use profile mode.
• Profile mode is deactivated on the emulator and simulator because their behavior is not typical of actual performance.
• Profile mode on mobile is comparable to deployment mode, with the following exceptions: - Some service extensions have been enabled, including the one that enables the performance overlay. - Tracking is enabled, and debugging tools (such as DevTools) that provide source-level debugging can connect to the process.
• When a web app is in profile mode, it signifies that: - The build has not been minified, but tree shaking has been conducted. - The dart2js compiler was used to create the app.
• The flutter run—profile command compiles in profile mode.

34. What is the release mode and when to use it in Flutter?

• When you want optimum optimization and a small footprint, deploy the program in release mode.
• When you're ready to deploy your app, switch to release mode.
• Release mode (which isn't available on the simulator or emulator) for mobile means: - Assertions are disabled. - Information about debugging is removed. - Debugging is turned off. - Compilation is geared at quick startup, execution, and compact package sizes. Extensions to the service have been disabled.
• When a web app is in release mode, it signifies the following: - The build has been minified, and tree shaking has been conducted. - For optimal performance, the app is built with the dart2js compiler.
• The flutter run—release command compiles in release mode.
• With flutter build target>, you can compile release mode for a specific target.

35. What are the constructors of Listview and when to use them?

•  ListView is a widget that enables us to view children in a given scroll direction one after the other. ListView has the following constructors:
• default ListView() returns a standard set of widgets scrolled from an explicit list. It's usually reserved for a limited group of children.
• For giant or infinite lists, use ListView.builder(). The itemCount parameter improves the ListView's ability to predict the maximum scroll extent.
• ListView.separated() is a function that works similarly to ListView.
• constructor(), on the other hand, allows you to design customized separators for each list item.
• ListView.custom() – Creates a custom child model for ListView. It gives ListView a lot more flexibility and control.

Conclusion

Our team presented these top Flutter interview questions and answers for you please comment below if you have any queries or suggestions.

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