Find a list of 100+ Flutter interview questions with answers

Welcome to the ultimate resource for acing your Flutter developer interviews! Whether you're a junior Flutter developer, a mid-level Flutter developer, or a senior Flutter developer, this article is your comprehensive guide to preparing for interviews and boosting your chances of landing your dream Flutter job. We'll cover a wide range of Flutter interview questions and provide detailed answers to help you shine in your next interview. Dive into this treasure trove of knowledge and master the world of Flutter development.

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Over time, I will make sure to keep this list updated with newer API changes, features, and updates. If you feel there is anything I missed or is wrong, please let me know in the comments below, and I will update this article as soon as possible.

Also, if you want to stay up to date with the latest changes, the GitHub version of this article can be found here.

Flutter Interview Questions by Positions

This article will cover Flutter Interview questions broken down by 3 skill levels:

Flutter Interview Questions by Overview

To give a short overview of the type of questions covered in this article, I have listed to most common Interview questions for Flutter Interviews below:

Fundamental Concepts of Flutter

Flutter important Interview concepts for Junior Positions

Are you just starting your journey as a Flutter developer? In this section, we've curated a collection of essential Flutter interview questions tailored to junior positions. From fundamental concepts to basic widget knowledge, these questions will help you establish a solid foundation for your Flutter career. Some topics covered include:

Flutter important Interview concepts for Mid-level Positions

If you've gained some experience and are aiming for mid-level Flutter positions, this section is tailored to you. We've compiled intermediate-level Flutter interview questions to test your knowledge and skills. Topics covered here include:

Flutter important Interview concepts for Senior Positions

For seasoned Flutter developers aiming for senior roles, this section is your gateway to advanced interview questions that will challenge your expertise. Topics covered include:

In each section, we'll not only provide you with the interview questions but also offer detailed answers and explanations to help you grasp the concepts thoroughly.

Flutter Interview Questions with Answers

Flutter important Interview concepts for Junior Positions

Question 1: What is a Widget in Flutter?

In Flutter, a widget is the fundamental building block of the user interface (UI). It is a lightweight and reusable component that can be assembled to create the overall UI of a mobile or web application. Widgets can represent anything from simple elements like buttons and text to complex layouts and interactive components.

Widgets in Flutter are categorized into two main types:

Widgets in Flutter follow a hierarchical structure, forming a widget tree. The root of the tree is typically a stateless widget called MyApp or similar, and it contains other widgets nested inside. Flutter uses a mechanism called the "Reconciliation" process to efficiently update only the parts of the UI that have changed, making it highly performant.

Widgets can also have properties or attributes that allow customization and parameterization, making them versatile for various UI design needs. They can be styled, aligned, and composed to create complex UI layouts.

Question 2: What are stateful and stateless widgets in Flutter?

Flutter is a UI toolkit that provides a way to build natively compiled applications for mobile, web, and desktop from a single codebase. Widgets are the fundamental building blocks of Flutter applications. Two crucial types of widgets in Flutter are Stateful and Stateless widgets, each serving a distinct purpose in the UI development process.

Stateful Widgets:

Example

class CounterWidget extends StatefulWidget {
  @override
  _CounterWidgetState createState() => _CounterWidgetState();
}

class _CounterWidgetState extends State<CounterWidget> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: <Widget>[
        Text('Counter: $_counter'),
        ElevatedButton(
          onPressed: _incrementCounter,
          child: Text('Increment'),
        ),
      ],
    );
  }
}

Stateless Widgets:

Example

class GreetingWidget extends StatelessWidget {
  final String message;

  GreetingWidget({required this.message});

  @override
  Widget build(BuildContext context) {
    return Text(message);
  }
}

Question 3: What are the more popular state management techniques in Flutter?

The Flutter official documentation provides a comprehensive overview of state management options available for Flutter developers. It covers various state management techniques and their use cases. It's a valuable resource for developers of all levels to understand the different options and choose the one that best fits their project requirements. Some of the most used state management techniques are mentioned below:

1. setState (To manage ephemeral states)

Answer: setState is a method provided by Flutter's State class. It is used to manage the state of a widget. When you call setState, it triggers a rebuild of the widget, updating the UI to reflect changes in the state. It's primarily used for managing ephemeral or local component-level state within a widget. This means it's suitable for managing small bits of state that don't need to be shared between multiple widgets or persisted.

2. Bloc (business Logic and component):

Answer: BLoC (Business Logic Component) is an architectural pattern in Flutter that separates the business logic of an application from the UI. It uses streams and sinks to handle data flow and events. BLoC has three main components: Events (user actions or input), States (representing the UI state), and the BLoC itself (which processes events and emits new states). It's a more advanced pattern suitable for managing complex UI states and handling asynchronous operations.

3. Provider

Answer: Provider is a state management solution that comes with Flutter and is often used for dependency injection and state management. It's more lightweight than BLoC and is excellent for managing the state of individual widgets or small-to-medium-sized applications. Provider uses a hierarchical approach to make data available to parts of the widget tree that need it. It's flexible and straightforward, making it a good choice for many Flutter projects.

4. Redux

Answer: Redux is a predictable state management container for Flutter (and other platforms). It is based on a unidirectional data flow pattern and involves actions, reducers, and a store. Redux is suitable for managing the state of large and complex applications where you need strict control over how data changes and is propagated throughout the app. It's often used in conjunction with libraries like Flutter Redux.

5. Fish Redux

Answer: Fish Redux is a Flutter application framework based on the Redux state management pattern. It is designed for building medium to large applications. Fish Redux simplifies the development of complex apps by providing a clear structure and separation of concerns. It's suitable for experienced developers working on sizable projects.

6. GetIt

Answer: GetIt is a service locator-based state management approach that doesn't require a BuildContext. It's primarily used for dependency injection, making it easy to access services and dependencies across different parts of your Flutter app. While it's not a state management solution in the traditional sense, it's often used in conjunction with other state management techniques.

7. MobX

Answer: MobX is a state management library that applies reactive principles to manage the state of your Flutter application. It allows you to create observable objects that automatically notify when their state changes. MobX is suitable for projects where you want a more reactive and declarative approach to state management.

8. InheritedWidget & InheritedModel

Answer: InheritedWidget is a Flutter widget that allows data to be passed down the widget tree efficiently. It's often used in cases where you have shared state that needs to be accessed by multiple widgets in the widget tree. InheritedModel is an extension of InheritedWidget that provides finer-grained control over which parts of the widget tree should rebuild when state changes. These are core Flutter concepts and should be understood by all Flutter developers.

9. Riverpod

Answer: Riverpod is a Flutter state management library that offers a more intuitive and flexible way of managing and accessing the state in your application. It's built on top of Provider and offers features like automatic disposal of objects and easy scoping of state. Riverpod is suitable for developers who want an improved Provider-like experience with added features.

Read the official documentation on Flutter's most popular state management techniques here:

Question 4: What are the differences between Flutter and React Native?

Flutter and React Native are both popular frameworks for building cross-platform mobile applications, but they have different approaches and characteristics. Here are the key differences between Flutter and React Native:

Both Flutter and React Native have their strengths and weaknesses, and the choice between them depends on project requirements, team expertise, and specific use cases.

Question 5: What is Flutter, and why is it gaining popularity in mobile app development?

Flutter is an open-source UI software development toolkit created by Google. It is used for building natively compiled applications for mobile, web, and desktop from a single codebase. Flutter gained popularity in mobile app development for several reasons:

In summary, Flutter's popularity stems from its speed, efficiency, single codebase approach, and the ability to create visually stunning, high-performance apps for multiple platforms. Its active community and continuous development by Google contribute to its ongoing growth and adoption in the mobile app development industry.

Question 6: Explain the key difference between Flutter and other mobile app development frameworks.

Flutter and traditional native app development differ in several key aspects:

Development Language:

UI Components:

Development Environment:

Code Reusability:

Development Time:

Performance:

Community and Ecosystem:

Learning Curve:

Integration:

In summary, Flutter simplifies cross-platform development by using a single codebase, provides a rich set of UI components, and offers features like hot reload for faster development. Traditional native development provides more platform-specific control but requires separate codebases and development environments for Android and iOS. The choice between them depends on project requirements and development priorities.

Question 7: Explain the concept of "State" in Flutter and how it differs from "Props" in React Native.

In Flutter, "State" refers to the mutable data that can be used to build and update the user interface (UI) of an app. It represents the dynamic aspects of an app, such as user interactions, data fetching, and UI changes in response to user input. Understanding the concept of State is fundamental in Flutter development.

Key points about State in Flutter:

Now, let's discuss how State in Flutter differs from "Props" in React Native:

To summarize, State in Flutter is used to manage mutable data within a widget and is crucial for dynamic UI updates, while Props in React Native are used for passing read-only data from parent to child components during component initialization. Understanding these concepts is essential for building interactive and responsive user interfaces in both Flutter and React Native.

Question 8: What is the purpose of the pubspec.yaml file in a Flutter project?

The pubspec.yaml file in a Flutter project serves several essential purposes:

In summary, the pubspec.yaml file in a Flutter project is a critical configuration file that manages dependencies, project metadata, assets, and other settings necessary for the development and distribution of your Flutter app. It helps Flutter tools understand how to build and package your app correctly.

Question 9: Can you name some of the basic widgets in Flutter?

These are just a few of the basic widgets in Flutter. Flutter's extensive widget library offers many more widgets for various UI needs, making it a powerful framework for building mobile and web applications.

Question 10: What is the difference between stateful and stateless widgets in Flutter?

In Flutter, widgets are classified into two main categories: Stateful Widgets and Stateless Widgets. These categories refer to how a widget manages and handles its internal state, which affects how they behave and update in response to changes in your app.

1. Stateless Widgets:

dartCopy codeclass MyTextWidget extends StatelessWidget {
  final String text;

  MyTextWidget(this.text);

  @override
  Widget build(BuildContext context) {
    return Text(text);
  }
}

2. Stateful Widgets:

dartCopy codeclass MyCounterWidget extends StatefulWidget {
  @override
  _MyCounterWidgetState createState() => _MyCounterWidgetState();
}

class _MyCounterWidgetState extends State<MyCounterWidget> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: <Widget>[
        Text('Counter: $_counter'),
        ElevatedButton(
          onPressed: _incrementCounter,
          child: Text('Increment'),
        ),
      ],
    );
  }
}

Question 11: How do you create a new screen or page in a Flutter app?

In Flutter, you create a new screen or page by defining a new widget that represents that screen/page, and then you typically navigate to this new widget when a user action, like tapping a button, indicates a transition to a different screen. Here are the general steps to create a new screen or page in a Flutter app:

That's it! When you tap the button associated with Navigator.push(), it will push the new screen onto the navigation stack, and you'll see the content of your MyNewScreen widget. Users can navigate back to the previous screen using the back button provided by Flutter's navigation system.

Question 12: Explain the concept of "hot reload" in Flutter.

"Hot reload" is a key feature in Flutter that allows developers to make real-time code changes and see the results almost instantly without restarting the entire application. It significantly speeds up the development process and enhances the developer's workflow. Here's a more detailed explanation of the concept of "hot reload" in Flutter:

Question 13: What is the purpose of the setState method, and how is it used?

In Flutter, the setState method is a fundamental part of managing the state of a widget and triggering a rebuild of the user interface when that state changes. It plays a critical role in making your UI responsive to changes in data or user interactions. Here's an explanation of the purpose of the setState method and how it is used:

Purpose of setState: The primary purpose of setState is to signal to the Flutter framework that the internal state of a widget has changed and that it should rebuild (redraw) the widget's user interface to reflect this new state. It helps maintain a reactive UI by associating changes in data or variables with corresponding updates in the UI.

How setState is used:

In summary, the setState method in Flutter is used to update the internal state of a widget and ensure that the user interface reflects those changes. It's essential for creating dynamic and responsive UIs, especially in stateful widgets where the UI depends on changing data or user interactions.

Question 14: Describe what a Flutter layout is and how it is structured.

In Flutter, a layout is a fundamental concept that defines how widgets are organized and displayed within the user interface. It determines how widgets are positioned, sized, and aligned within the constraints of their parent widgets. Understanding Flutter layouts is crucial for designing user interfaces that adapt to various screen sizes and orientations. Here's an explanation of what a Flutter layout is and how it is structured:

What is a Flutter Layout?
A Flutter layout is a way of arranging and positioning widgets to create the visual structure of a user interface. It's how you specify the visual hierarchy and relationships between different widgets, such as arranging text, images, buttons, and other elements on the screen. Flutter provides a flexible and composable system for creating layouts that work across different devices and screen sizes.

Structure of a Flutter Layout:

Question 15: How do you handle user input, such as a button press, in Flutter?

In Flutter, you can handle user input, such as a button press, through event handling and callbacks. Event handling in Flutter is typically associated with widgets like buttons and gesture detectors. Here's a step-by-step guide on how to handle user input, specifically button presses, in Flutter:

That's the basic process of handling user input, specifically button presses, in Flutter. You create a button widget, define the onPressed callback, handle the user's input within that callback, and update the UI as needed. Depending on your app's complexity, you might also need to consider state management for maintaining and updating the app's state.

Question 16: What is the purpose of the main() function in a Flutter app?

In a Flutter app, the main() function serves as the entry point of the application. It is the starting point of the program's execution and is where the Flutter framework initializes and runs the app. Here's a breakdown of the purpose of the main() function in a Flutter app:

Here's a simple example of a main() function in a Flutter app:

dartCopy codeimport 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'My Flutter App',
      home: Scaffold(
        appBar: AppBar(
          title: Text('Welcome to Flutter'),
        ),
        body: Center(
          child: Text('Hello, Flutter!'),
        ),
      ),
    );
  }
}

In this example, the main() function initializes the app by running an instance of MyApp, which is a custom widget representing the main structure of the app's UI. The runApp() function is used to start the app and render the UI defined by MyApp. This is a basic structure, and as your Flutter app becomes more complex, you may also configure routing, state management, and other features within the main() function or delegate them to other parts of your codebase.

Question 17: How do you style widgets in Flutter?

Styling widgets in Flutter involves defining how a widget should look in terms of visual properties such as colors, fonts, padding, and more. Flutter provides several ways to style widgets, including:

These are some of the common ways to style widgets in Flutter. Depending on your project's complexity and design requirements, you may use a combination of these methods to achieve the desired styling for your widgets.

Question 18: Explain what a Flutter package is and give an example of when you might use one.

In Flutter, a package refers to a collection of Dart code and resources that provide specific functionality or features that can be easily integrated into your Flutter app. These packages are typically distributed via the Dart package manager called Pub, making it simple to include third-party code and functionality into your Flutter projects. Packages can range from simple utility libraries to complex UI components and are essential for enhancing your app's capabilities and saving development time.

Here's an example of when you might use a Flutter package:

Example: Using a Package for State Management

Suppose you're developing a Flutter app that requires complex state management to handle user authentication, global app settings, and data persistence. Instead of building all of these state management features from scratch, you can leverage a third-party package like provider or Bloc:

By using packages like provider or flutter_bloc, you can significantly reduce development time and effort while ensuring that your Flutter app is efficient and maintainable.

Packages in Flutter extend beyond just state management; they cover various aspects of app development, including UI components, networking, database integration, and more. You can explore the official Flutter package repository to discover packages that suit your project's needs and leverage the Flutter community's collective expertise to build powerful and feature-rich mobile applications.

Question 19: What is the Flutter widget tree, and why is it important?

The Flutter widget tree is a hierarchical structure that represents the user interface (UI) of a Flutter application. It is a fundamental concept in Flutter and plays a central role in how Flutter apps are built and displayed on the screen. Understanding the Flutter widget tree is crucial for Flutter developers because it forms the foundation for creating dynamic and responsive user interfaces.

Here's why the Flutter widget tree is important:

Overall, the Flutter widget tree is at the heart of Flutter's declarative and reactive programming model. It simplifies UI development, promotes code reusability, and enables developers to create high-performance, platform-agnostic, and customizable user interfaces. Mastery of this concept is crucial for building efficient and visually appealing Flutter applications.

Question 20: How do you navigate between screens in a Flutter app?

In Flutter, you can navigate between screens or pages using a package called Navigator. Navigator manages a stack of pages, and you can push and pop pages onto and off this stack to achieve screen navigation. Here's a step-by-step guide on how to navigate between screens in a Flutter app:

This basic approach should help you navigate between screens in your Flutter app. You can further enhance navigation with features like passing data between screens, handling routes, and implementing custom transitions.

Question 20: Describe the purpose of the BuildContext in Flutter.

In Flutter, BuildContext is a fundamental concept that represents the location of a widget in the widget tree. It provides access to information about the location, state, and configuration of the widget within the widget hierarchy. Understanding the purpose of BuildContext is crucial for building efficient and responsive Flutter applications. Here's a breakdown of its main purposes:

Question 21: What is the purpose of the async and await keywords in Flutter, and how are they used?

In Flutter (and Dart, the programming language Flutter is built with), the async and await keywords are used to work with asynchronous operations. Asynchronous operations are tasks that don't block the main thread of your application, allowing it to remain responsive while the task is being executed. Here's an explanation of their purpose and how they are used:

Here's how you typically use async and await in Flutter:

It's important to note that you should use async and await judiciously in your Flutter code. While they make working with asynchronous operations more readable, using them excessively or inappropriately can lead to performance issues or blocking the main thread. Additionally, always handle errors that might occur during asynchronous operations using try and catch to ensure your app remains robust.

Question 22: How do you make an HTTP request in a Flutter app?

Question 23: Explain what Flutter plugins are and provide an example of a plugin you might use.

Question 24: What is the purpose of the Future class in Flutter, and how do you handle asynchronous operations?

Question 25: How can you handle errors and exceptions in a Flutter app?

Question 26: Describe the process of adding assets, like images or fonts, to a Flutter project.

Question 27: What is the purpose of the ListView widget, and how do you create a scrollable list in Flutter?

Question 28: How do you persist data locally in a Flutter app, and what options are available for data storage?

Question 29: Explain the concept of "widget keys" in Flutter and when you might use them.

Question 30: What are Flutter themes, and how do they help maintain consistent app styling?

Question 31: How can you test your Flutter app, and what tools are available for testing?

Question 32: Describe the purpose of the BuildContext in Flutter and how it is used in widget composition.

Question 33: What are some best practices for organizing code and project structure in a Flutter app?

Flutter important Interview concepts for Mid-level Positions

Explain Flutter's Architecture

Flutter's architecture is designed to provide a robust and flexible framework for building natively compiled applications for mobile, web, and desktop from a single codebase. Understanding Flutter's architecture is crucial for developing efficient and maintainable Flutter applications. Flutter's architecture can be broken down into several key components:

Read more about Flutter's Architecture here.

What are platform and Method channels?

Flutter, known for its seamless cross-platform development, often needs to interact with platform-specific features or functionalities that are not part of its core framework. This is where platform channels and method channels come into play.

Platform Channels:

Platform channels in Flutter act as a bridge or communication channel between the Flutter codebase and the native code of the underlying platform (Android and iOS). They allow you to send data and messages back and forth between the Flutter application and the platform-specific code.

Here's how platform channels work:

Method Channels:

Method channels are a specific type of platform channel. They enable you to invoke platform-specific methods or functions from your Flutter code. Here's how they work:

In summary, platform channels and method channels are essential tools in Flutter's toolbox for integrating with native platform functionalities. They enable Flutter developers to access and utilize platform-specific features while maintaining the cross-platform nature of their applications. This flexibility is crucial when building robust and feature-rich apps that need to tap into the full potential of both the Flutter framework and the underlying platforms.

Read more about Writing custom platform-specific code here.

What is JIT and AOT? What are the differences between the two?

JIT (Just-In-Time) and AOT (Ahead-Of-Time) are two different compilation techniques used in the context of programming languages and runtimes. They are often associated with Flutter because Flutter uses both JIT and AOT compilation for different purposes during app development and deployment. Here's an explanation of each and the differences between them:

JIT (Just-In-Time) Compilation:

AOT (Ahead-Of-Time) Compilation:

Differences:

In Flutter, the combination of JIT during development for fast iteration and AOT during production for optimal performance and smaller binary size provides a balance between development convenience and app performance.

Flutter important Interview concepts for Senior Positions

How does Flutter render Widgets?

The answer to this question was described beautifully at the Google Developer Days China 2019 presentation by Andrew Fitz Gibbon and Matt Sullivan:

How Flutter Renders Widgets - Insights from Google Developer Days China 2019

Flutter's rendering of widgets is a fundamental aspect of how it creates beautiful and performant user interfaces. In the Google Developer Days, China 2019 presentation by Andrew Fitz Gibbon and Matt Sullivan, the inner workings of Flutter's rendering process were dissected to provide a deeper understanding of this powerful UI framework.

In conclusion, Flutter's ability to render widgets efficiently is a result of its widget tree, elements, and render objects working together harmoniously. This architecture, as explained in the Google Developer Days China 2019 presentation, empowers developers to build high-performance, visually stunning applications across multiple platforms. Understanding this rendering process is key to becoming proficient in Flutter app development.

How does Flutter run my code on Android?

Flutter's execution of code on the Android platform involves a multi-step process that seamlessly blends native Android components with Flutter's own framework. Here's a breakdown of how it works:

Compilation Process:

Integration into the Android Project:

Runtime Execution:

Debug Mode and Hot Reload:

During the development phase, Flutter provides a "debug mode" that employs a virtual machine (VM) to execute your code. This VM enables a powerful feature known as "stateful hot reload." With hot reload, you can make live changes to your code without requiring a full recompilation. It's a valuable tool for rapid development and debugging.

However, it's important to note that the "debug" banner displayed in the top right-hand corner of your app during this mode serves as a reminder that the app's performance might not accurately represent the final release version. Debug mode prioritizes developer convenience and agility over performance optimization.

In summary, Flutter's execution on Android is a sophisticated process that leverages AOT compilation, seamless integration, and a dynamic runtime environment. This approach allows developers to build and iterate on high-quality, cross-platform applications efficiently while harnessing the power of Flutter's unique features like hot reload during development.

How does Flutter run my code on iOS?

Flutter, renowned for its exceptional cross-platform capabilities, achieves seamless code execution on iOS through a well-orchestrated process that bridges the gap between its Dart-based framework and the iOS ecosystem. Here's an insight into how Flutter runs your code on iOS:

Compilation with LLVM:

The heart of Flutter's magic lies in its engine. The C and C++ components of this engine are meticulously compiled using LLVM (Low-Level Virtual Machine), a robust compiler infrastructure highly regarded for its efficiency and optimization capabilities.

Ahead-of-Time Compilation (AOT):

Dart, the language behind Flutter, undergoes ahead-of-time (AOT) compilation. This process compiles both the Dart Software Development Kit (SDK) and your application's Dart code into native code specifically tailored for the ARM architecture. This compiled code is packaged into a native library.

The Runner iOS Project:

To create a functional iOS app, Flutter employs an "iOS runner" project. Within this project, the native iOS elements are integrated seamlessly with Flutter's compiled native code. The result is an iOS Application Package (IPA) containing the entire application.

Loading the Flutter Library:

Upon launching your Flutter app on an iOS device, the application dynamically loads the Flutter library. This library acts as the bridge between your Flutter code and the underlying iOS platform. It ensures that all essential components, including rendering, input handling, and event management, are routed to the appropriate compiled Flutter and application code.

Debug Mode and Stateful Hot Reload:

During the development process, Flutter introduces a valuable feature known as "debug mode." In this mode, a virtual machine (VM) comes into play to execute your Dart code. This VM enables a powerful capability called "stateful hot reload." With stateful hot reload, you can make real-time changes to your code without requiring a full recompilation. It significantly enhances the development workflow.

However, it's worth noting that while operating in debug mode, you'll encounter a "debug" banner in the top right-hand corner of your app. This banner serves as a friendly reminder that the performance experienced during debugging may not fully represent the efficiency of the final release app.

In conclusion, Flutter's ability to execute code on iOS seamlessly combines the strengths of Dart, native iOS components, and a carefully orchestrated compilation process. This amalgamation ensures that your Flutter apps on iOS deliver high-performance, cross-platform functionality while retaining the convenience of stateful hot reload during development.

Flutter Interview questions and answers pdf

If you want to get all of these Flutter interview questions and answers in a pdf document, download it here.