Are you looking for the best flutter interview questions and answers? Then you’ve arrived at the right location. Flutter is a user interface toolkit that allows you to create beautiful, fast, and natively compiled mobile apps with a single codebase and programming language. Dart is a general-purpose programming language based on the C programming language. The Dart programming language is primarily used to create frontend user interfaces for mobile and web apps.

To make your interview process go more smoothly, we’ve compiled a list of frequently asked Flutter developer Interview questions based on expert opinions. This set of Flutter and Dart interview questions. This article combines the queries for flutter interview questions for freshers and flutter interview questions for the experienced and hence its appropriate for both beginners and professional developers. Preparing for these questions will boost your confidence and allow you to settle in the interview.

TOP 40 FLUTTER INTERVIEW QUESTIONS & ANSWERS

  1. Tell me what you know about Flutter?

Flutter is a user interface toolkit for building natively compiled mobile apps with a single programming language and codebase. It is a Google-developed open-source development framework. Flutter is an SDK, not a programming language. The Dart programming language is used to create Flutter apps. Flutter’s first alpha version was announced in May of 2017.

Flutter is primarily designed for 2D mobile apps that run on both Android and iOS. It can also be used to generate full-featured apps with the camera, storage, geolocation, network, third-party SDKs, and other features.

2. Explain to me about Dart?

Dart is a C-style object-oriented programming language with a general-purpose syntax. It was created by Google in 2011 and is open-source. Dart programming is used to build frontend user interfaces for web and mobile applications. It’s a fundamental language for developing Flutter apps. Dart can be compiled both in AOT (Ahead-of-Time) and JIT (Just-in-Time) (Just-in-Time).

3. Tell us more about Flutter widgets?

A Flutter app is often thought of as a collection of widgets. Every time you code in Flutter to construct something, you’ll do so within a widget. Widgets explain how the current configuration and state of your app should appear. When you made a change to the code, the widget reconstructed its description by calculating the difference between the previous and current widgets to determine the smallest changes for app UI rendering.

To build the app, widgets are nested within each other. It means your app’s root is a widget, and anything below it is a widget.

4. Tell us about stateful widgets?

State information is stored in a Stateful widget. It’s called dynamic because the inner data will change during the widget’s lifetime. A Stateful widget is a widget that helps us to refresh the screen. There is no build() technique for this widget. It has a createState() method that returns a Flutter State Class. Checkbox, Radio, Slider, InkWell, Form, and TextField are examples of Stateful widgets.

5. What are stateless widgets?

There is no state information in the Stateless widget. Throughout its lifespan, it remains static. Text, Row, Column, Container, and other Stateless widgets are examples. It should be a Stateless widget if the screen or widget contains static content, so it should be a Stateful widget if the content needs to be changed.

6. List the best Flutter development tools used?

The Flutter development tools are the ones that allow the Flutter developers to make Flutter development rapid and secured and thus stimulating the developer’s workflow. To create mobile applications, the Flutter IDE and tools need some plugins. Dart compiling, code analysis, and Flutter development are all made easier with the plugins. The following are some of the most popular IDEs for Flutter development:

  • Android Studio

  • Visual Studio

  • IntelliJ IDEA

  • Xcode

7. Explain about Tween Animation?

Tween Animation is the shortened version for in-between animation. In tween animation, you must specify the start and endpoints of the animation. This enables the animation to begin at the beginning and progress through a series of values until it reaches the endpoint. The tween animation also determines the transition’s speed and duration.

8. List the popular apps that use Flutter?

Flutter has grown in popularity and acceptance as the most widely used and accepted tool for developing apps. The following are some of the most popular Flutter apps.

  • Google Ads

  • Alibaba

  • Coach Yourself

  • Watermaniac

  • Reflect

  • Birch Finance

  • Tencent

9. Explain pubspec.yaml file?

The project’s configuration file will be used frequently when dealing with the Flutter project. It gives you control over how your app works. It also allows us to set the app’s constraints. This file contains the following information:

  • The name, description, and version of the project are all general project environments.

  • Dependencies on the project.

  • Assets for the project (e.g., images, audio, etc.).

10. Define an App state and list its examples?

The App State is also known as a shared state or an application state. The app state can be shared across different sections of your app, and user sessions are maintained in the same way.

The following are some App State examples:

  • Information on how to log in

  • Preferences of the user

  • An e-commerce application’s shopping cart

  • Notifications from social media

  • On news apps, there is a read/unread state of information.

11. How to create HTTP requests in Flutter?

Use the HTTP package to create HTTP requests. (import ‘package:http/http.dart’ as http;). This has an appropriate method for making a request:

http.get(‘https://jsonplaceholder.typicode.com/albums/1‘);

This will return a Future<http.Response>.

12. Explain Flutter packages and their plugins?

A package is a collection of classes, interfaces, and sub-packages that are all of the same types. Packages and plugins allow us to create the app without having to write all of the code ourselves. It is possible to import new widgets or functionality into a Flutter app. There isn’t much of a difference between packages and plugins.

Plugins allow more usability on the device by using native code, while packages are new components or code written in dart languages. Packages and plugins are both related as packages in the DartPub.

13. Why is Flutter UI focused?

Flutter is said to be UI-focused since it has an excellent user interface because it uses a design-centric widget, advanced APIs, high-development tools, and many more features.

15. What is the point of making separate directories for iOS and Android in a flutter project?

ANDROID: This folder is for storing a complete Android project. When creating a Flutter framework for the Android platform, this will come in handy. When you compile Flutter code into native code, it is imported into an Android project, resulting in a native Android app.

iOS: This folder is for storing a complete Mac project. When creating a Flutter program for the iOS platform, this will come in handy. It functions in the same way as the Android folder. When you compile Flutter code into native code, it is imported into the Android iOS project, resulting in a native Android app. Working with the Xcode IDE and macOS is the only way to build a Flutter program.

15. Tell us about Hot Reload in flutter?

The hot reload function helps you to experiment with the project quickly and easily. It aids in the creation of user interfaces, the addition of new features, the correction of bugs, and the rapid development of apps. Follow these steps to perform a hot reload of a Flutter app:

  • Run the app in a Flutter editor or terminal window that supports it.

  • Any Dart file in the project can be changed.

  • Select Save It all or click the Hot Reload button on the toolbar if you’re using an IDE that supports Flutter. You will immediately see the result in your simulator or on a real computer.

16. Mention the latest release of Flutter SDK?

The most recent version of the Flutter framework is v1.20.4, which was released on September 15, 2020.

17. What are the well-known database packages used in flutter?

The following are the most commonly accepted and widely used database packages in Flutter:

Firebase: A user can access and modify the cloud database using the Firebase database.

Sqflite: A user can access and modify the SQLite database using the sqflite database.

18. How will you utilize This keyword in Dart?

In Dart, this keyword refers to the present instance of the category .

void main() {

Car c1 = new Car(‘E1001’);

}

class Car {

String engine;

Car(String engine) {

this.engine = engine;

print(“The engine is : “);

}

}

19. What are the advantages of a Flutter Inspector?

  • Choose a widget mode.

  • Toggle the platform to reveal the paint baselines.

  • Debug paint should be visible.

  • Widget refresh

  • Slow animations should be allowed.

  • Activate or deactivate the output overlay.

20. How to define a generic extension in Dart?

This could be done by adding a template parameter, like the below,

extension MyFancyList<T> on List<T> {

int get doubleLength => length * 2;

List<T> operator -() => reversed.toList();

List<List<T>> split(int at) => <List<T>>[sublist(0, at), sublist(at)];

}

21. How do you create a factory?

Factory constructors are developed by using the factory keyword. They can return subtypes or even null.

e.g., factory User.fromXml(String xml).

22. List the responsibilities of FlutterActivity?

FlutterActivity is an Android app that shows a Flutter experience. The different roles of a FlutterActivity are as follows:

  • The Flutter flash screen and the Android launch screen are shown.

  • It alters the appearance of the status bar.

  • It chooses Flutter’s first direction.

  • It chooses an entry point and the execution path for the Dart app bundle.

  • Transparency may be added to the Activity if needed.

23. List the different types of grid view available in Flutter?

The different forms of grid views available in Flutter are as follows:

  • count()

  • custom()

  • builder()

  • extend()

24. Explain Broadcast streams in Flutter?

This stream is for single messages that can be processed one at a time. In a browser, these types of streams are widely used for mouse events. This sort of stream can be added to the list at any time. Multiple listeners can listen at the same time, and you can listen even though your previous subscription has been canceled.

25. Tell us about Single subscription streams available in Flutter?

It is a common and widely used stream. It is made up of a set of events that make up a larger whole. All events must be delivered in a specific order, with no single event being missed. When you get a web request or a file, you get this sort of stream. There is only one way to list this stream. Listing it over and over results in missed initial values, and the final stream makes little sense. The data is fetched and given in chunks when the listing begins in this stream.

26. Create a TextField with an initial value?

We can set a controller with an initial value like TextEditingController(text: “Initial Text”).

27. Tell me about Build context?

In Flutter, the BuildContext is a component of the widgets in the Element tree, with each widget having its BuildContext. It’s primarily used to get a connection to another widget or theme. If we want to use a material design feature, we must relate it to the scaffold, for example. Scaffold.of(context) method may be used to obtain it.

28. How will you declare async function as a variable in Dart?

Async functions are normal functions having variable type just specifies that it returns a Future:

class Example {

Future Function() asyncFuncVar;

Future asyncFunc() async => print(‘Do async stuff…’);

Example() {

asyncFuncVar = asyncFunc;

asyncFuncVar().then((_) => print(‘Hello’));

}

}

void main() => Example();

29. How will you use release mode in Flutter?

Release mode helps us to customize the codes and produce them in a completely configured state without any debug data. Many sections of the application’s code will be omitted or rewritten in this mode.

When we’re ready to release the software, we switch to this mode. It allows for optimal optimization and a limited device footprint.

To compile the release mode, run the following command:

flutter run –release

30. When would you use profile mode in Flutter development?

Our applications’ output is measured using profile mode. In this mode, you can still debug and profile the output of your app. Since the emulator and simulator are not indicative of real-world output, this mode is disabled.

To compile the profile mode, use the following command:

flutter run –profile

31. Why do you need Mixins?

Multiple inheritances are not supported in Dart. Mixins are important to formulate multiple inheritances in Flutter/Dart. Mixins allow you to write the code for a reusable class in multiple class hierarchies.

32. Explain Ticker in Flutter?

In Flutter, a ticker represents the rate at which our animation is refreshed. It’s a signal-sending class that sends a signal at a set frequency, such as 60 times per second. Our watch, which tics at regular intervals, helps us grasp it. Ticker offers a callback method for each tick that has the length since the first ticks at each second since it was started. Even if the tickers began at different times, they are immediately synchronized.

33. Explain Stream in Flutter?

A stream is a set of asynchronous events that happen at the same time. It generates an asynchronous data series. It’s like putting any value on one end of a pipe, and if there’s a listener on the other end, it will receive that value. We can keep several listeners in a stream, and when they’re all placed into the pipeline, they’ll all get the same benefit.

The Stream API’s await for and listen() methods can be used to process a stream. It has a mechanism for dealing with errors. Streams can be created in a variety of ways, but they can all be used in the same way. Consider the following condition:

Future<int> sumStream(Stream<int> stream) async {

var sum = 0;

await for (var value in stream) {

sum = sum + value;

}

return sum;

}

34. Explain main() and runApp() functions in Flutter?

The main() function is in charge of getting the program started. We can’t write a Flutter program without the main() function.

The runApp() function is vital for returning the widgets that are connected to the screen and will be made on the screen as a root of the widget tree.

35. Explain the ‘?’ operator in detail?

The “?” operator calculates and returns the difference in value between two expressions based on the given condition. It can be used in the following ways:

condition ? expr1 : expr2

This operator tests the condition first, then evaluate expr1 and returns its value if it is valid (if the condition is matched). Otherwise, it evaluates expr2 and returns its value.

36. Explain Hot Restart in Flutter?

It primarily functions with the importance of States. Since it removes the retained State values and sets them to their defaults, it allows developers to get a completely compiled program. Our app widget tree is rebuilt with the freshly typed code on every Hot Restart.

37. How to create Extensions?

Extension methods add new functionalities to any type, even those from the basic level. They are introduced earlier in Dart 2.7 and are already available to use in Flutter as well. Check the below code to create extensions,

extension NumberParsing on String {

int parseInt() {

return int.parse(this);

}

}

38. Explain Null aware pointers?

Dart has some helpful tips for dealing with null values.

1. The “??=” assignment operator, which only assigns a value to a variable if it is null.

int x; // Initial value of a is null.

x??= 2;

print(x); // It will print 2.

2. The null-aware “??” operator evaluates and returns the value between two expressions. It checks expression 1 and returns its value if it is not null; otherwise, it evaluates and returns the value of expression 2:

print(4 ?? 5); // It will print 4.

print(null ?? 5); // It will print 5.

39. What is the use of the Await function?

Await is only used within async. It puts all currently running functions on hold until pf nature is done.

40. How can you run code in debug mode only?

To run the code in debug mode only, we must first import the dart foundation as shown below:

import ‘package:flutter/foundation.dart’ as Foundation;

Next, use the kReleaseMode as shown below:

if (Foundation.kReleaseMode){ // is Release Mode ??

print(‘release mode’);

} else {

print(‘debug mode’);

}

Now, you came across the above are the top-ranging flutter interview questions 2021.

FINAL WORDS BEFORE YOUR INTERVIEW:

Every company nowadays has an app to advertise their services and increase sales. This has resulted in a strong demand for Flutter and Dart, as well as a rise in the number of opportunities in this area. I hope you found this Flutter interview questions blog to be informative. Also, Our NSCHOOL Academy Technical experts are well supportive enough to guide you throughout the flutter development training course journey. Good luck with your studies and interview for the flutter developer!