Flutter Interviews - Imtiaz211/interviews GitHub Wiki

Flutter Interview Questions and Answers

  1. Why is Flutter preferred over other mobile app developing tools?

Flutter is a free and open-source mobile UI framework, introduced by Google in May 2017. Flutter enables you to develop a native mobile app using only one codebase. This implies you may design two separate apps using the same programming language and codebase (for iOS and Android). Flutter is preferred over other mobile app development tools like Java and React Native due to a myriad(ˈमिरिअड्)बहुत बड़ी संख्या,अनगिनत of reasons. A few of them are: Flutter supports cross-platform development Programming in Flutter is extremely easy and flexible The building process in Flutter is much faster than that in all its competitors.

  1. What are packages and plugins in Flutter?

A package is a set of classes, interfaces, and sub-packages that allow users to create modular code that can be shared easily. Instead of starting from scratch, using packages can help construct applications fast. In Flutter, you may use a package to add new widgets or functionality to an app. On the other hand, a plugin is a piece of software that enhances your app's functionality. Plugins play a crucial role in the Flutter ecosystem.

  1. What are the limitations of Flutter?

Since Flutter is still a relatively new tool, it has some limitations. They are as follows:

  • The number of third-party libraries is very small
  • The release size of Flutter is larger than expected
  • Flutter requires to be used along with another OOP language, Dart which cannot compete with other OOP languages such as Java, C#
  • Due to Flutter’s limited complexity, mobile ad platforms do not support it
  • Flutter is still not used by a wide audience
  1. Why does it generally take a long time to develop a Flutter app?

Because Flutter generates a device-specific IPA or APK file, building a Flutter application takes substantially longer the first time. This method, which normally takes a long time, uses Xcode and Gradle to build a file.

  1. What are keys and how do you use them?

A set of IDs for Widgets, Elements and SemanticsNodes make up the key class. Keys are responsible for preserving the state of widgets when they are updated inside the widget tree. Keys may also be used to modify and rearrange collections of widgets of the same type and defined states. Otherwise, keys may be superfluous to the code, even if they aren't harmful in any manner. Keys are useful when you need to edit a widget tree with stateful widgets, but not when the tree is entirely made up of stateless widgets.

  1. What are the different types of streams in Dart?

Streams provide an asynchronous sequence of data. Asynchronous programming uses the idea of streams. They refer to a program's asynchronous succession of data occurrences. We put a value on one end and a listener on the other, similar to a pipe. Several listeners can be combined into a single stream, and when they are placed in the pipeline, they will all get the same data. It is possible to utilize the SteamController to establish new streams or manage existing ones. There are two types of streams:

Single Subscription Streams These streams convey events in chronological order. They're thought of as individual sequences inside a greater totality. When the sequence in which events are received matters, such as when reading a file, these streams are employed. Throughout the sequence, there can only be one listener, and the event will not be triggered if there isn't one. Broadcast Streams These broadcasts provide subscribers with information about upcoming events. Subscribers can instantly begin listening to events after subscribing to them. These are flexible streams that allow several listeners to listen at the same time. Furthermore, even after canceling a previous membership, one may listen again.

  1. What is pubspec.yaml file?

While creating a Flutter project, a particular type of file is always included at the top of the project. This file is known as the pubspec.yaml file, also called pubspec. This file contains information about a project's dependencies, such as packages and their versions, typefaces, and so on. It ensures that the package version is the same the next time you create the project. You can also place restrictions on the app. This project's configuration file will be used a lot while working with the Flutter project. This specification is written in YAML, a human-readable markup language.

  1. What is Flutter?

Flutter is an open source software development kit (SDK) UI used for cross-platform applications from a single codebase. Flutter is primarily used for creating natively compiled, multi-platform applications across iOS and Android seamlessly.

  1. Flutter is developed by which company?

Google

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

Sky is the first version of Flutter which ran on Android OS. It was announced at the 2015 Dart developer summit with the stated goal of being able to render consistently at 120 frames per second.

  1. 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
  1. 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.

  1. 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.

  1. 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
  1. Which operator is used to evaluate and return values between two expressions?

This “??” operator is used to evaluate and return values between two expressions. This operator first checks the expression 1 and, if it is non-null, returns its value; otherwise, it will evaluate and return the value of expression 2.

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

There are two main types of widgets in Flutter. These include:

  • StatelessWidget- It does not have any state information. It is static throughout its lifecycle. Examples are Row, Text, Column, and Container.

  • StatefulWidget- It has state information. It contains two classes: the state object and the Widget. It is dynamic because it can change the inner data during the Widget's lifetime. Examples are Radio, Form, Checkbox, and TextField.

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

This command Flutter run -- release is used to compile the release mode. Release mode for a web app means that the app is compiled with the dart2js compiler for best performance.

  1. Name the different types of build modes in Flutter.

There are three types of build modes in Flutter. These include:

  • Debug- It is used to test the apps. On Android Studio, you can find a green play button on the top panel. “Flutter run”

  • Profile- In this mode, some debugging ability is maintained - enough to profile your app's performance, and also, it has the performance as the release mode. “Flutter run -- profile”

  • Release- It is used for deploying the app on marketplaces. “Flutter run - - release”

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

SizedBox is a widget in Flutter that allows us to specify an arbitrary size for a widget. It is basically used to add empty space between widgets. SizedBox also supports specifying a specific aspect ratio for its child.

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

The choice of animation in Flutter would depend on the specific behavior that needs to be represented. Flutter provides several animation options that can be used to represent real-world behavior. These include Physics-based animation, Tween animation, Curved animation, and Hero animation.

  1. Name some popular apps that use Flutter?

Some of the most popular apps that employ Flutter include:

  • Google Ads, Hamilton, KlasterMe, Reflectly
  1. Which folder is used to write Android apps in Flutter?

Android Folder is used to write Android apps in Flutter. The Android Folder contains files and folders required for running the application, and these files are autogenerated during the creation of a Flutter project.

  1. What is the use of the Await function?

The Await function is an asynchronous function. Its job is to wait until it gets the final value. Await is used with async functions and that run asynchronously, giving users the choice to wait for the asynchronous mode to finish before continuing.

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

In Flutter, there are several functions and commands that can be used to compile and update the app. However, the most commonly used function for this purpose is hot reload. Hot reload is a development feature in Flutter that allows you to update your app's code in real-time, without restarting the entire app.

  1. 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.

  1. What is the purpose of animation controller class in Flutter?

The Animation Controller class in Flutter is used to control and manage animations. It provides a way to start, stop, or pause an animation, and allows you to define the duration, speed, and direction of an animation.

  • The primary purpose of the Animation Controller class is to define an animation that can be used in your app's user interface. The class provides methods for defining and manipulating animations, such as setting the duration and the curve used to control the animation's progress.
  1. How can you test a single Widget?

Using the Widget tests technique, you can make sure that various portions of the user interface work as intended without the need for a physical device or simulator. This technique is the best way to isolate small parts of your app and find out whether your code is behaving as expected

  1. Can you use WidgetsApp for basic navigation?

Yes, a material app widget builds a navigator, which manages a stack of widgets identified by strings, also known as routes objects and gives you two ways for managing the stack.

  1. Which widget allows us to refresh the screen?

RefreshIndicator Widget enables us to refresh the screen. When the user pulls down on the widget, the onRefresh callback is triggered, which typically involves fetching new data from a server or updating the UI in some way.

  1. Can you state a few examples of stateless widget?

Some examples of a stateless widget include the following:

  • Text - This displays a string of text with a single style.
  • Container: This widget can contain other widgets and provide padding, margins, and other layout properties.
  • Icon - This is used for the list of available material icons that can be used with this class.
  1. Explain the term “Tree shaking” in Flutter?

Tree shaking is a method of removing the unused module in the bundle during the development process. Tree shaking serves as a sort of optimization technique that optimizes the code by removing the dead code.

  • While importing or exporting codes, there might be dead codes hanging around. Removing these dead codes reduces the code size which in turn improves the performance of the application.
  1. What is used to import packages for your project?

pubspec.yaml file is used to import packages in the Dart code. It allows us to set the constraints for the application. This file contains project dependencies, general project settings, and project assets.

  1. 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.

  1. Why HTTP package is used in Flutter?

HTTP package is used in Flutter for making HTTP requests to web servers. It allows Flutter developers to send HTTP requests and receive HTTP responses from APIs or web servers. Flutter apps need to communicate with APIs or web servers to fetch data or send data to the server. The HTTP package provides a convenient and easy-to-use way to make HTTP requests in Flutter.

  1. Explain profile mode in Flutter?

The profile mode in Flutter is used to test the functionality of an app while launching it. It compiles and launches your app almost identically to release mode but with additional functionality to allow debugging performance problems.

  1. What's the role of BuildContext in Flutter?

In Flutter, the BuildContext is an object that provides access to the location of a widget in the widget tree hierarchy and to various services such as Theme, MediaQuery, and Navigator. The BuildContext is used by widgets to access the properties of their parent widget, such as its size, position, and theme. It is is also used to navigate between screens using the Navigator widget.

  1. 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 is a widget in Flutter that is used to implement the basic material design visual layout structure. The scaffold class makes it faster to create a general-purpose mobile application. Moreover, it contains almost everything we need to create a functional and responsive Flutter application.

  1. Can you tell us what will be the default return type, if you don’t specify the return type for a function?

This means, if you declare a function in Flutter without specifying a return type, Dart assumes that the function can return any type of value and assigns the dynamic type to the return value by default.

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

The name of a constructor for a class is the same as that of the class itself. Constructor is a special strategy that is used to create objects with predetermined values for the properties. There are three types of constructors in Flutter: named constructor, standard constructor, and factory constructor.

  1. What’s the core of the Flutter layout mechanism?

The main core of the Flutter layout mechanism is the Widgets. The widgets are the building blocks of the user interface, and they are arranged in a tree-like structure known as the widget tree. The image, text, icon, and even the layout of your application are all widgets.

Only questions.

1.stateless vs stateful

  1. What are stateful widget lifecycle methods?

  2. Difference between final, const and static

  3. How do you validate a form in Flutter?

  4. State management.

  5. Any exp with HTTP requests? any package used? Or maybe a Firebase?

  6. What are keys?

  7. What is the extension method? Do you use them? Why they are great?

  8. What is isMounted property, why is it important, when to use it?

  9. What is a mixin? When to use it?

  10. How do you handle l10n in your apps?

  11. How do you theme your app?

  12. ThemeData, ColorScheme, or something else?

  13. How do you handle dark mode?

  14. What if you use MaterialApp but want to use the Cupertino widget?

  15. What is sound null safety? Why is it important? How to enable it?

  16. What is Navigator 2.0?

  17. How do constraints work in Flutter, general rule?

  18. How do you provide accessibility when developing Flutter apps

  19. Async model in Dart

  20. How do futures work? (Event loop)

  21. How does Flutter rendering work, I mean widget tree?

  22. Does dart have a reflection mechanism?