Top Flutter Interview Questions

Aspiring developers diving into the world of mobile app development often find themselves drawn to Flutter, Google’s open-source UI software development kit. Flutter’s popularity stems from its ability to craft beautiful, high-performance applications for multiple platforms, including Android, iOS, and even the web, using a single codebase. However, mastering Flutter requires more than just coding skills; it demands a profound understanding of its intricacies and nuances. One crucial aspect of preparing for a Flutter developer role is tackling a range of interview questions that delve into various aspects of the framework, from its fundamental concepts to its advanced features and best practices.

In this comprehensive guide, we’ll explore a curated selection of Flutter interview questions designed to help you sharpen your knowledge and ace your next interview. Whether you’re a beginner looking to break into the field or an experienced developer aiming to level up your Flutter expertise, these questions will cover key topics such as widget hierarchy, state management, platform-specific integrations, performance optimization, and more. By familiarizing yourself with these questions and their answers, you’ll not only boost your confidence but also gain valuable insights into Flutter’s capabilities, enabling you to tackle real-world challenges with ease and finesse.

Flutter Interview Questions

Why is Flutter preferred over other mobile app developing tools?

Flutter is a mobile UI framework that was created by Google back in May 2017. The cool thing about Flutter is that you can build a native mobile app using just one codebase. This means you can create two different apps (one for iOS and one for Android) using the same programming language and code. There are a lot of reasons why Flutter is a popular choice for mobile app development compared to other tools like Java and React Native. Some of them include:

Flutter allows for cross-platform development
It’s really easy and flexible to program in Flutter
The building process is much faster than with other tools So if you’re looking to develop a mobile app, Flutter might be the way to go!

What are packages and plugins in Flutter?

In programming, a package is a collection of classes, interfaces, and sub-packages that enable users to develop modular code that can be easily shared. By utilizing packages, developers can expedite the process of building applications without having to start from square one. For instance, within Flutter, packages can be utilized to incorporate new widgets or features into an application. Conversely, a plugin is a software component that extends the capabilities of an application. Plugins play a vital role in enhancing the functionality of apps within the Flutter ecosystem.

What are the limitations of Flutter?

Flutter is a relatively new tool with some limitations. These include: –

A small number of third-party libraries
Larger than expected release size
Dependence on Dart, which may not be as competitive as other OOP languages like Java or C#
Limited support from mobile ad platforms due to Flutter’s complexity
Low adoption by a wide audience.

Why does it generally take a long time to develop a Flutter app?

When creating a Flutter app, it may take longer initially as it generates a device-specific IPA or APK file. The process typically involves using Xcode and Gradle to build the file, which contributes to the extended duration of the initial build.

What are keys and how do you use them?

In programming, a set of identifiers for Widgets, Elements, and SemanticsNodes form the key class. Keys play a crucial role in maintaining the status of widgets as they undergo updates within the widget hierarchy. They can also be employed to manipulate and reorganize groups of widgets with identical characteristics. While keys may not always be essential in the code, they do not pose any harm either. They come in handy particularly when dealing with stateful widgets in a widget hierarchy, as opposed to a structure consisting solely of stateless widgets.

What are the different types of streams in Dart?

Streams are a cornerstone of asynchronous programming, offering a pathway for data to flow asynchronously through a program. Conceptually, streams represent a sequence of data occurrences unfolding asynchronously. Picture them as pipelines: one end receives a value, while the other end, equipped with a listener, awaits to process it. Streams support the aggregation of multiple listeners, ensuring all receive the same data when integrated into the pipeline. Managing streams, whether creating new ones or controlling existing ones, can be achieved through the StreamController utility.

There are two main categories of streams: Single Subscription Streams and Broadcast Streams. Single Subscription Streams maintain a strict order of events, ideal for scenarios where event sequence matters, like reading from a file. Notably, only one listener can be active at a time, and events won’t trigger without one present. On the other hand, Broadcast Streams disseminate information about upcoming events to subscribers, enabling immediate event consumption upon subscription. These streams are versatile, accommodating multiple simultaneous listeners, and even allowing re-subscription after previous cancellations.

What is pubspec.yaml file?

When you start a new Flutter project, you’ll always find the pubspec.yaml file at the top. This file, commonly referred to as ‘pubspec’, holds important details about the project’s dependencies like packages and their versions, fonts, and more. It helps in maintaining consistency in package versions for future project creation and allows for setting constraints on the application. The pubspec.yaml file is an essential part of Flutter development, written in YAML – a user-friendly markup language.

What is Flutter?

It’s a free software development kit (SDK) for creating applications that work on both iOS and Android with just one codebase. Flutter lets you build apps that run smoothly on both platforms, making it a popular choice for developers.

Flutter is developed by which company?

Google

What was the first version of Flutter which ran on an Android operating system?

The first version of Flutter, known as Sky, was developed to run on the Android operating system. It was introduced at the 2015 Dart developer summit, aiming to provide smooth rendering at a high frame rate of 120 frames per second.

Can you tell us the four main elements of Flutter?

The four main elements of Flutter are:
• Flutter engine
• Widgets
• Design-specific widgets
• Foundation Library

When was the first version of Flutter released?

The first version of Flutter was released in May 2017, but it was first announced in 2015. In December 2018, Google released Flutter 1.0. In December 2019, Flutter 1.12 was released.

Flutter is written in which language?

Flutter was written in the Dart language. While writing and debugging an application, Flutter runs in the Dart virtual machine, which features a just-in-time execution engine.

What does the acronym SDK stand for?

A Software Development Kit (SDK) consists of various software tools and programs offered by software and hardware vendors for developers to create applications for specific platforms. SDKs assist developers in seamlessly integrating their apps with a vendor’s services by providing APIs, sample code, documentation, and additional resources to aid in the creation of software applications.

Can you name some best editors for Flutter development?

Some popular IDEs (Integrated Development Environment) for Flutter include the following:

Android Studio
IntelliJ Idea
Emac
Visual Studio
Codemagic

Which operator is used to evaluate and return values between two expressions?

The double question (??) mark operator is used to compare and choose values between two expressions. It looks at the first expression and, if it’s not empty, returns that value. If it is empty, it will then evaluate and return the value of the second expression.

Can you tell us how many kinds of widgets there are in Flutter?

In Flutter, there are two main types of widgets:

StatelessWidget: These widgets do not have any state information and remain static throughout their lifecycle. Examples include Row, Text, Column, and Container.
StatefulWidget: These widgets have state information and consist of two classes – the state object and the Widget. They are dynamic as they can modify the inner data during the Widget’s lifetime. Examples include Radio, Form, Checkbox, and TextField.

Can you name the command used to compile the release mode?

When you run the command “Flutter run –release”, it compiles the app in release mode. Compiling in release mode for a web app entails using the dart2js compiler to optimize performance.

Name the different types of build modes in Flutter.

There are three different modes for building apps in Flutter:

Debug Mode: This mode is used for testing apps. You can easily run your app in Debug mode by clicking on the green play button in Android Studio. The command to run in Debug mode is “Flutter run”.
Profile Mode: In this mode, some debugging functions are still available for profiling your app’s performance. It offers similar performance to Release mode. The command to run in Profile mode is “Flutter run –profile”.
Release Mode: This mode is used for deploying your app to marketplaces. The command to run in Release mode is “Flutter run –release”.

Which widget in Flutter is a box that comes with a different size?

In Flutter, SizedBox is a handy widget that lets us set a custom size for a widget. It is primarily used to create spacing between widgets. Additionally, SizedBox allows us to define a specific aspect ratio for its child element.

Suppose you have to represent real world behavior in Flutter, which animation would you use?

When it comes to choosing animation in Flutter, it really depends on the type of behavior you want to show. Flutter offers a variety of animation choices that can mimic real-life movements, such as Physics-based animation, Tween animation, Curved animation, and Hero animation.

Name some popular apps that use Flutter.

Some of the most popular apps that employ Flutter include:

Google Ads
Hamilton
KlasterMe
Reflectly

Which folder is used to write Android apps in Flutter?

The Android Folder in Flutter is where developers write Android apps. It includes all the necessary files and folders for running the application, which are automatically generated when creating a new Flutter project.

What is the use of the Await function?

The Await function is designed to wait for the final value in asynchronous functions. It is used with async functions that run asynchronously, allowing users to choose to wait for the asynchronous process to complete before proceeding.

Can you tell us which function compiles and updates the app?

Flutter provides a variety of functions and commands to compile and update the app, with hot reload being the most popular option. This feature in Flutter enables developers to instantly update the app’s code without having to restart the entire application.

Can you tell which function is accountable for starting the program?

main () function is used to start a program. This function is highly critical as, without it, one cannot write any function.

What is the purpose of animation controller class in Flutter?

The Animation Controller class in Flutter is responsible for handling animations in your app. It allows you to easily control and manage animations by starting, stopping, or pausing them, as well as defining their duration, speed, and direction. This class is essential for creating dynamic user interfaces in your app, as it provides the necessary methods for defining and controlling animations. You can set the duration and curve of an animation to customize its behavior and progres

How can you test a single Widget?

By utilizing the Widget tests technique, you can confidently verify that different components of the user interface are functioning properly without relying on a physical device or simulator. This method is highly effective in identifying specific areas of your app and determining if your code is performing as anticipated.

Can you use WidgetsApp for basic navigation?

Yes. A material app widget creates a navigator that controls a stack of widgets labeled by strings, referred to as routes objects, and provides two methods for handling the stack.

Which widget allows us to refresh the screen?

The RefreshIndicator Widget allows users to refresh the screen by pulling down on the widget. This triggers the onRefresh callback, which usually involves fetching new data from a server or updating the UI.

Can you state a few examples of stateless widget?

Here are a few examples of stateless widgets: –

Text: This widget shows a text string with a consistent style.
Container: This widget can hold other widgets and offer padding, margins, and layout properties.
Icon: This widget displays a list of material icons that can be utilized within this class.

Explain the term “Tree shaking” in Flutter.

During the development process, tree shaking is a technique used to eliminate any unused modules from the bundle. This optimization method helps to streamline the code by getting rid of unnecessary portions. When importing or exporting codes, there can be lingering dead codes that are not being utilized. By removing these dead codes, the overall size of the code is reduced, leading to enhanced performance of the application.

What is used to import packages for your project?

The pubspec.yaml file is essential for importing packages in Dart code. It helps in setting constraints for the application by specifying project dependencies, general project settings, and project assets.

What’s the use of Navigation.push in Flutter?

The role of Navigation.push in Flutter is to add a route to a bundle of other routes which are managed by the navigator.

Why HTTP package is used in Flutter?

The HTTP package in Flutter is utilized for sending HTTP requests to web servers. This enables Flutter developers to interact with APIs or web servers by sending and receiving HTTP responses. For Flutter apps to retrieve or send data to servers, they must communicate with APIs or web servers. Thankfully, the HTTP package offers a user-friendly and convenient method for sending HTTP requests within Flutter applications.

Explain profile mode in Flutter?

In Flutter, the profile mode is a useful tool for testing an app’s functionality during its launch. It behaves similarly to release mode but with added features that help identify and solve performance issues.

What's the role of BuildContext in Flutter?

When working with Flutter, the BuildContext is a crucial object that allows widgets to interact with their surroundings in the widget tree and access important services like Theme, MediaQuery, and Navigator. This context helps widgets grab information about their parent widgets, like size, position, and theme. It also enables seamless navigation between different screens using the Navigator widget.

Can you tell us which class is responsible for implementing the basic material design visual layout structure for an app in Flutter?

The scaffold class in Flutter is like a building block for creating the visual layout of a mobile application following material design guidelines. It simplifies the process of building a versatile and interactive app by providing all the necessary components.

What’s the name of a constructor for a class in Flutter?

In Flutter, a class’s constructor shares the same name as the class itself. Constructors are special methods employed to initialize objects with predefined property values. There are three varieties of constructors in Flutter: named constructors, standard constructors, and factory constructors.

What’s the core of the Flutter layout mechanism?

In Flutter, the foundation of the layout system lies within the Widgets. These components serve as the essential elements of the user interface, organized in a hierarchical structure referred to as the widget tree. Whether it be an image, text, icon, or the overall layout of your app, each element is represented as a widget.

Which widget can be used to display one after another in scroll format?

The ListView Widget is designed to showcase numerous items in a scrollable list. It serves as an upgraded version of the Column widget, offering automatic scrolling when the item list exceeds the screen size.

What is a layout in Flutter?

In Flutter, a layout describes how widgets are positioned on the screen based on constraints provided by the parent widget. It sets the location and dimensions of the child widget.

Can you tell us how we can test a single widget in Flutter?

Widget tests are essential for creating and using widgets in a testing setting. They help verify if the widget functions correctly. With this tool, you can easily test a specific widget.

What’s the latest version of Flutter?

The most recent release of Flutter is version 3.7. This update includes enhancements to the framework as well as exciting new features such as improved support for material 3, cascading menus and menu bars, impeller preview, custom context menus, and updates to DevTools.

May 8, 2024