Flutter Interview Questions and Answers for 2023

Flutter has been around since Google first launched it in early 2015, but the hype around it has only recently grown stronger due to the grow in its community. Flutter is a Google UI toolkit that helps us create beautiful, natively compiled applications for mobile (Android, iOS), desktop (Linux, Mac, Windows), and web from a single codebase. One of the coolest things about Flutter framework is how fast we can deliver a market-ready digital product. The developers of Flutter made sure that the tool is fast for mission-critical applications. They used fast object-oriented programming language (Dart), created its own rendering engine (Skia), and made the framework extensible with third-party plugins with extensive focus on features and UI elements. Many companies such as Google, ByteDance, Philips, Tencent, and Groupon, also use Flutter to create their applications and hire Flutter developers as it makes an ideal solution for building cost-effective cross-platform apps.

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Beginner

This is a frequently asked question in Flutter developer interview questions.  

Flutter is a popular open-source and cross-platform mobile UI framework developed by Google. All Flutter applications make use of Dart programming language. Flutter is portable and helps us to create elegant iOS and Android apps. Flutter has a very extensive widget library, with hundreds of complex and customized widgets that can help us to generate 2D motions and UI animations in our application.

The low-level parts in Flutter framework like Flutter engine are mostly written in C/C++.The Flutter Framework is written in Dart programming language which is object-oriented. The Dart compiler and VM which is used during development are also written in C/C++. Some Android interaction code in Flutter is written in Java programming language and some iOS interaction code is written in Objective-C programming language.

Expect to come across this popular question in Flutter interview.  

Flutter framework has many advantages, you can tell some of the pros of using Flutter are that it has a rich collection of widgets that makes applications look great. We can also use Flutter web for creating web apps like progressive web apps (PWAs) and single-page applications (SPAs).  

Another advantage can be that Flutter has excellent documentation and support from the development team, which makes it easy to learn and use for any beginner. You can also say that it helps us to build versions of the application for different platforms from a single source code. 

A must-know for anyone heading into a Flutter interview, this question is frequently asked in Flutter basic interview questions.  

We can tell some disadvantages, such as developing an application in Flutter has a higher degree of difficulty. Another disadvantage could be that it can be difficult to find Flutter developers while collaborating on a project. Also, it has fewer features for working with graphics in your project, and the applications created using the Flutter framework are large and complex.

We can say that SDK has no use on its own but is only helpful when writing applications for one particular software or platform. In other words, an SDK is only a tool to write an application, whereas a framework becomes part of an application.

Now let us see the Flutter interview question and answers for freshers. These can also be termed as Flutter interview questions for beginners that are asked by the interviewer while hiring for a Flutter developer.

Flutter is not a programming language, it is a software development kit with prewritten code consisting of ready-to-use and customizable widgets, as well as library tools, and documentation that together serve to build cross-platform apps.

Flutter is a framework specifically designed for the frontend, as such there is no “default” backend for a Flutter application. Back endless was among the first no-code/low-code backend services to support a Flutter frontend.

It's no surprise that this one pops up often in interview questions for Flutter developer.  

Yes, Flutter supports web content generation using standard-based web technologies: HTML, CSS, AND JavaScript. Based on the web support, we can compile the existing Flutter code written in Dart into a client experience embedded in the browser and deployed to any web server.

Dart is an object-oriented programming language developed by Google. It is similar to JavaScript but has a few additional features and is much faster than JavaScript. It is a compiled language and uses a JIT compiler while compiling the code. It is also easy to learn and has a slight learning curve. Dart is a dynamic, and type-safe language that also supports inheritance and interfaces.  

Dart has a built-in exception system and an extended keyword. Dart also supports interfaces, mix-ins, and static typing during development. It can be used in web, mobile, and server-side development and in companies like Dart like Blossom, Google, Tencent, and Alibaba. The best thing about Dart programming language is that it has an easy learning curve, and the documentation is excellent.  

The functions in Dart are usually based on a do-while loop, which tests a condition at the end of the loop iteration. This loop is similar to the for loop in JavaScript. 

A common question in Flutter basic interview questions, don't miss this one.  

Async means that this function is asynchronous, and you might need to wait a bit to get its result. Await literally means - wait here until this function is finished, and you will get its return value. Future is a type that 'comes from the future' and returns a value from your asynchronous function. It is a potential value or error that will be available in the future after some time.  

SizedBox is a widget available in Flutter SDK. It can be defined as a simple box with a specified size. It is created using SizedBox() constructor and is used to set size constraints to the child widget or to put an empty SizedBox between the two widgets so that we get some space in between, or something else. The SizedBox widget in Flutter is somewhat similar to the Container widget but with fewer properties.  

One of the most frequently posed Flutter developer interview questions, be ready for it.  

If we are using a column, then MainAxis is y i.e., it aligns the widgets vertically with respect to the value of “MainAxis”, the value can be start, center or end and if we are using a row, then MainAxis is X i.e., it aligns the widgets horizontally with respect to the value of “MainAxis,” the value here also can be start, center, or end.

Packages in Flutter are "shared packages that are shared by other developers to the Flutter and Dart ecosystems. This enables developers to quickly create an application without having to start from scratch." A "package" is simply Dart code.

A plugin can be defined as a piece of software that adds additional capabilities to our app. For example, sometimes we might want our mobile app to interact with the camera on our device. Plugins are an important part of the Flutter ecosystem. To see if the plugin we need already exists, we have to check pub. Dev.

Tickers are used to send signals at constant frequencies to help developers determine the frequency of animation refreshes in Flutter. We can think of Ticker as a special periodic timer that can be used to be notified when the Flutter engine is about to draw a new frame.  

To create a ticker, we first need to add a SingleTickerProviderStateMixin to our State subclass. Tickers in Flutter can be used by any object that wants to be notified whenever a frame triggers but are most commonly used indirectly via an AnimationController. The AnimationControllers need a TickerProvider to obtain their Ticker. 

The Flutter cookbook includes all the instructions required for resolving typical issues that arise when developing Flutter apps. Each step can be used as a reference to construct an application because it is self-contained.

When we develop applications using the Flutter framework, we create a single logic and design. We do not have to invest in creating separate design interfaces when working with Flutter. You can easily create a single code and interface and share it with all OS. Basically, we will not need to invest in platform-specific UI to build the interface. 

Also, when we are developing with Flutter, we tend to increase the development speed and reduce the time. With this framework, we can quickly build and test applications, thus allowing us a quicker launch into the market. The reason that developers nowadays like Flutter framework is the way it offers native-like performance.  

It enhances the user experience by using components similar but different from the user interface. Even in the most complex interface animations, we tend to get a native-like experience. This is also a commonly asked basic Flutter interview question. 

Flutter is a free and open-source user interface software development kit. This toolkit includes its own rendering engine (Skia), many unit and integration testing APIs, plugin APIs, and command-line tools for building and compiling apps, it also has rich set of ready-made widgets in addition to a react-style framework.  

The following is available inside the Flutter SDK, you can say any five of them. Dart SDK is a heavily optimized, mobile-first 2D rendering engine that has excellent support for text, it is a modern react-style framework for applications, and it uses APIs for unit and integration tests.  

In this Interop and plugin APIs are used to connect to the system, and 3rd-party SDKs, and a headless test runner is used for running the tests on operating systems such as Windows, Linux, and Mac, the Dart DevTools available to us is used for testing, debugging, and profiling our developed application, Flutter and dart command-line tools are used for creating, building, testing, and compiling our applications, it also has a rich set of widgets that implement various Material Design and iOS styles.

We are expected to have good knowledge of native Android development: that is if we want to develop very fine and detailed applications in Flutter. Also, we should have a solid understanding of OOPS(Object-Oriented-Programming) concepts.

We should be well versed with appropriate knowledge of Git and the use of GitHub, candidates should understand the fundamentals of Computer Science, understand the software development life cycle, have strong knowledge of different architecture approaches, and knowledge of SQL as a database is equally important.

My experience with Flutter was very nice. The most important advantage that I get by developing apps with Flutter is that I can modify or customize the widgets with much ease than as compared to other frameworks. It is also comparatively faster than the already existing frameworks, which reduces the overall application development time. The widgets provided in Flutter are helpful which are important for web application design requirements. The Flutter framework is extremely scalable as it uses Google Firebase on the backend. As it is open-source framework, it has attracted a large and very active developer community all around the world, this makes it easier to collaborate on the projects. 

Now we will see the Flutter interview question and answers for intermediate developers. These can also be termed as Flutter interview questions for experienced that are asked by the interviewer while hiring a Flutter developer. 

Intermediate

Streams and sinks are backbones in Dart and Flutter asynchronous programming. Streams provide an asynchronous sequence of data. These data sequences include user-generated events and data read from files. We can process a stream using either await for or listen() from the Stream API. Streams provide us a way to respond to errors. There are two kinds of streams: single subscription streams and broadcast streams. 

If we want to create a stream where we can put a value on, we start with the StreamController. 

Code-  

StreamController<double>Controller= StreamController<double>(); 
We can access the controller’s stream by making use of the stream property. 
Code- Stream stream=controller.stream; 

A staple in Flutter interview questions, be prepared to answer this one.  

In Flutter there are two types of widgets. 

  • Stateless Widget- A widget where we don't get option to alter its page once it’s built is called as stateless widget. Stateless widget is like final keyword where once created we can’t update or change it. And it is always recommended to use stateless widget when we don't want to update State. You can give the examples like text and icons, buttons. 
  • Stateful Widget- Stateful widgets are the opposite of Stateless widgets. In this we can alter the page after it is built. You can give examples of stateful widget as Checkbox, Radiobutton, TextField, Form. 

The Flutter's profile mode compiles and launches our application similarly to the release mode, but with just enough additional functionality that allows us to debug performance problems. For example, profile mode provides tracing information to the profiling tools. For compiling the profile mode, the command required is Flutter is run --profile command.

This question is a regular feature in Flutter developer interview questions, be ready to tackle it.  

As Dart language belongs to the same group as Java, C#, Swift, Scala, Kotlin, etc. The languages in this group share some concepts like Static Typing, Garbage Collector & Object-Oriented Programming and they are used in developing business applications. The special thing about Dart is the things related to the Implementation of the language. 

Features like the Ahead-of-Time (AOT) compiler + VM & Just in Time (JIT) compiler together (where we have the choice) and Generational Garbage Collector are good things for implementing features like Hot reload in the Flutter Framework without sacrificing the performance when distributing the application. Dart is also helpful because it enables developers to handle exceptions gracefully. Aside from its many valuable features, Dart also has a surprisingly extensive library. 

The new features in Flutter 2 are the support for the web platform, the Add-to-app feature which enables us to take advantage of Flutter by adding it in our existing iOS and Android applications, the sound null safety feature, and the ever-growing ecosystem around Flutter such as Adobe’s introduction of XD to Flutter and Microsoft’s increasing support for the Flutter framework.  

Flutter 2 makes it easier for developers to monetize their created applications through in-app purchases, ads, and payments, to connect to cloud services and APIs that extend apps to support new capabilities. It has tools and language features that allow the removal of a lot of errors, which results in enhanced app performance and reduced package size. 

AppWrite Flutter is based on the Dart programming language and uses the Skia graphics library. This allows developers to create apps that look and feel natural on both iOS and Android devices. It is used for beautiful cross-platform mobile apps. It is designed to help developers build high-quality apps that are both responsive as well as reliable. AppWrite Flutter is still in the early phase of development, but there are already many existing apps built with it.  

These include the popular to-do app Todo-MVC and the open-source note-taking app Evernote. If we want to build cross-platform mobile apps, then AppWrite Flutter is worth checking out. 

While the traditional frameworks available nowadays depend upon the OEM widgets of the device or they utilize the web view, Flutter on other hand uses its own high-performance rendering engine that renders every view component. This is the reason we can create Flutter-based applications that come with native-like performance characteristics.  

C/C++ code of the engine is compiled with LLVM ("Low-Level Virtual Machine) on iOS and NDK (Native-Development Kit) on Android. During the process of compilation, the Dart code is Ahead-Of-Time (AOT)-compiled into regular native code. The steps involved in the working of Google Flutter in a simplified way are as follows: 

  • Step 1: When building an app on the Flatter framework, we can use it with either a Stateful widget or Stateless widget. 
  • Step 2: These Widgets are then rendered onto Skia canvas and sent to the platform. 
  • Step 3: The canvas is then shown to us by the platform. 
  • Step 4: The events are sent back according to the need.

This is a frequently asked question in Flutter interview questions. 

  • Debug Mode: The Debug mode in Flutter is used to debug the physical device, emulator, or Simulator. In this mode assertions and service extensions are enabled. The Compilation process is optimized for fast deployment. This process is enabled, and tools supporting source-level debugging can connect to the process. In the debug mode, Flutter optimizes the app to reflect changes faster. 
  • Profile Mode: The Profile Mode in Flutter is used to analyze the performance of our app. Here, some extensions and tracing are enabled. The Profile mode is disabled on the emulator and simulator because their behavior is not representative of real performance. 
  • Release Mode: The Release mode in Flutter is enabled to deploy our app. Here, assertions, service extensions, and debugging are disabled. The compilation process is optimized for fast startup, execution, and package sizes. This mode is used to deploy the app when we want maximum optimization and minimal footprint size. It is designed to get our app ready for the Play Store and App Store. 

The crossAxisAlignment property in Flutter determines how row and column can position their children on their cross axes. A row’s cross-axis is vertical, and a column’s cross-axis is horizontal. The crossAxisAlignment property has five values which are mentioned below: 

  • CrossAxisAlignment.start- It positions the children near the start of the cross-axis. (Top for Row, Left for Column) 
  • CrossAxisAlignment.end- It positions the children near the end of the cross-axis. (Bottom for Row, Right for Column) 
  • CrossAxisAlignment.center- It positions the children at the middle of the cross-axis. (Middle for Row, Center for Column) 
  • CrossAxisAlignment.stretch- It stretches the children across the cross axis. (Top-to-bottom for Row, left-to-right for Column) 
  • CrossAxisAlignment.baseline- It aligns the children by their character baselines. (Text class only and requires that the textBaseline property is set to TextBaseline.alphabetic. 

Expect to come across this popular question in Flutter interview.  

Unit tests are used extensively for verifying the behavior of a single function, method, or class. The test package provides the core framework for writing unit tests, and the Flutter_test package provides additional utilities for testing the widgets. 

The core features provided by the test package are accessed by using the following steps: 

  • Step 1- Adding the test or Flutter_test dependency. 
  • Step 2- Creating a test file. 
  • Step 3- Creating a class to test. 
  • Step 4- Writing a test for our class. 
  • Step 5- Combining multiple tests in a group. 
  • Step 6- Running the tests. 

A must-know for anyone heading into a Flutter interview, this question is frequently asked in Flutter technical interview questions.  

As its name proposes, it is utilized for testing a single widget, and the objective of the widget testing is to check whether the widget works and looks true to form. The widget test tests the UI components, so it is also called Component Testing. It is used to test a single widget. The main goal of widget testing is to check whether the widget works as expected or not. A user has the freedom to write test cases for every widget present in the project. 

We can tell the steps for widget testing as follows: 

  1. Adding the Flutter_test dependency. 
  2. Creating a widget to test. 
  3. Creating a testWidgets test. 
  4. Building the widget using the WidgetTester. 
  5. Searching for our widget using a Finder. 
  6. Lastly, verify the widget using a Matcher. 

It's no surprise that this one pops up often in Flutter developer interview questions.  

Unit tests and widget tests are useful for testing individual classes, functions, or widgets. However, they are unable to test how individual pieces of code work together as a whole or capture the performance of an application running on a real device. These tasks are then performed with integration tests.  

The Integration tests in Flutter are written using the integration test package, provided by the software development kit (SDK). It is Flutter's version of Selenium WebDriver (generic web), Protractor (Angular), Espresso (Android), or Earl Gray (iOS). The package internally uses a Flutter driver to drive the test on any device. 

The steps for Integration testing as follow: 

  • Step 1- Creating an application to test. 
  • Step 2- Adding the integration_test dependency. 
  • Step 3- Creating the test files. 
  • Step 4- Writing the integration test. 
  • Step 5- Finally, running the integration test. 

As far as Flutter is concerned, the following database packages are widely accepted and mostly used by the community. 

1- Firebase Database: It gives the users access and control over the cloud database. Firebase provides a NoSQL database for Flutter apps with the ability to manage data retrieval and storage through JSON protocol. Data sync and quick loading make it one of the most suitable options for Flutter Apps.  

Features in a Firebase database: 

  • NoSQL DB  
  • APIs (REST only)  
  • Authentication 
  • Analytics  
  • Storage  

2- SQFlite Database: We can access and modify the SQLite database using this. With this database, we have full control over our database, queries, relationships, and anything you could desire.  

Features in SQFlite database are as folows: 

  • Serverless  
  • Zero configuration  
  • Open-Source  
  • Compact  
  • Single DB file. 

In Flutter, a container is a widget that has the capacity to accommodate multiple child widgets and manage them efficiently through dimensions, padding, and background color. Whenever we want to style the background of a widget, either because of a shape, color, or size constraint, we may use a container widget.  

With the Container class, widgets can be stored and positioned on the screen at our discretion. In general, the container class resembles a box for storing contents. 

During development, a fast developer cycle is very important for iteration. The Dart VM offers a just-in-time compiler (JIT) that has features such as incremental recompilation (enabling hot reload), live metrics collections (powering DevTools), and rich debugging support. When apps are ready to be deployed to production—whether we are publishing to an app store or deploying to a production backend—the Dart ahead-of-time (AOT) compiler can compile to native ARM or x64 machine code.  

The AOT-compiled app launches with a consistent, short startup time. The AOT-compiled code runs inside an efficient Dart runtime that enforces the sound Dart type system and manages memory using fast object allocation and a generational garbage collector.  

Now, let us have a look at the Flutter interview question and answers for advanced developers who have a good command of Flutter development. These questions can also be termed Flutter advanced interview questions that are asked by the interviewer while hiring a Flutter developer. These questions are also called as Flutter senior interview questions as these are mostly asked for a senior position in an interview, but these questions can be asked to you as well, so never leave a void in your preparation. 

Advanced

The keys in Flutter are used as identifiers for widgets, elements, and semantic nodes. GlobalKey and LocalKey are the subclasses of the key in Flutter. We can find keys in every widget as named parameters. Inside the widget tree, keys are responsible for preserving the state of the modified widgets. With keys, we can also reorganize and modify collections of widgets that have an equivalent type and defined state.  

The main use of keys in Flutter is to modify a widget tree that contains stateful widgets, not to modify a widget tree that is totally composed of stateless widgets where states change. The example here that you can give is when we find ourselves adding, removing, or reordering a certain collection of widgets of the same type that hold some state, we use keys. The real-world application of the keys would be a Todo application.

A common question in Flutter interview questions and answers for experienced, don't miss this one. 

  • Hot Reload: The “hot reload” allows developers to inject source code modifications directly into a running app to be seen immediately, without requiring a restart or loss of state. This feature is very useful as it helps us avoid the lengthy compilation process, which is particularly irritating when developers need to apply small changes in the app. Not having to wait for who-knows-how-long for the code to compile only to discover that you left out a semi-colon when tweaking the color of a button seems like a significant change for developers. It takes one second to perform its functionality. 
  • Hot Restart: The “hot restart” loads the code changes into the VM and restarts the Flutter app, which results in losing the app state. It has a bit different functionality as compared to hot reload. In this, the preserved states of our app are destroyed, and the code gets compiled again from the beginning. Although hot restart takes longer than a hot reload, it's faster than a full restart function. 

One of the most frequently posed Flutter developer interview questions, be ready for it.  

Null-aware operators in Dart let us make computations based on whether the given value is null. Dart provides us with some useful information to handle the null values.  

Assignment operator("??="): The assignment operator assigns a value to a variable only if it is null. 

Code:- 

int a;                           // a is initialized with null value.   
a ??= 20;      
print(a);                      // It will print 20.  

Null-aware operator ("??"): The null-aware operator computes and returns the value between two expressions. In the first step, expression 1 is checked for the nullness condition, and if it is null, then it’s value is returned; otherwise, expression 2 is evaluated, and its value is returned. 

Code:- 

print(5 ?? 10);            // It will print 5.  
print(null ?? 10);       // It will print 10.  

Safe Navigation Operator(“?.”): The Safe Navigation operator is also known as the Elvis operator. It is possible to use the (?.) Operator when we call a method/getter on an object, if it isn't null (otherwise, the method will return null). 

Code:- 

obj?.child?.child?.getter . 

The use of FutureBuilder in Flutter is to create widgets based on the latest snapshot of interaction with Future. The Future must be obtained earlier through a change of state or a change in dependencies. FutureBuilder is a Widget that helps us to execute some asynchronous functions and based on that function’s result the user interface gets updated. FutureBuilder is used to check for the future state, whether the future is resolved or not, and so on. You can mention some states are mentioned below. 

  • ConnectionState.none: It means that the future is null and initial Data is used as default value. 
  • ConnectionState.active: It means the future is not null but it is also not resolved yet. 
  • ConnectionState.waiting: It means the future is being resolved, and we will get the result soon enough. 
  • ConnectionState.done: It means that the future has been resolved.  

A staple in Flutter interview questions for experienced, be prepared to answer this one.  

View, Interactor, Presenter, Entity, and Router. You can explain each one of them as following:

  • The user interface or UI is called the View. This is consistent with a view. 
  • A class called the Interactor acts as a go-between for the presenter and the information. It follows the presenter's instructions. 
  • The "traffic cop" of the architecture is the Presenter. By taking user actions and invoking the router to move the user between views, it directs the data between the view and interactor. 
  • Application data is represented by an Entity. 
  • The Router controls screen switching. 
  • The V.I.P.E.R pattern architecture is different from the usual model view architecture where we have full model data and view uses the data (also business logic uses the data). The full application object is in the memory. There is no application object in mobile development like other desktop-based applications.  

Horizontal Scroll in Flutter can be built by the following steps as follows: 

Firstly, we need to create a ListView widget that supports horizontal lists. So that we can use the standard ListView constructor, passing in a horizontal scrollDirection, which overrides the default vertical direction as shown below. 

Code: - 

ListView( 
scrollDirection: Axis.horizontal, 
children: [ 
Container( 
width: 100, 
color: Colors.green, 
), 
Container( 
width: 100, 
color: Colors.yellow, 
), 
Container( 
width: 100, 
color: Colors.blue, 
), 
Container( 
width: 100, 
color: Colors.black, 
), 
Container( 
width: 100, 
color: Colors.orange, 
), 
], 
), 

The Equatable is used to simplify the process of comparing the instances of the same object without the need for boilerplate codes of overriding “==” and hashCodes. It is a Dart package that helps to implement value-based equality without needing to explicitly override the “==” and hashCode. We can understand it with the following example. 

This helps compare two objects. Two different objects for equaltity. 

 Code: - 

class Person {  
int age;  
String name;  
double height;   
// constructor  
Person({this.age, this.name, this.height});  
 
//If we have three objects of this class like 
Person person1 = Person(17, "James", 6.2);  
Person person2 = Person(17, "Vince", 3.2);  
Person person3 = Person(17, "Peter", 6.2);  
Here person1 is not equal to person2, but it is the same as person3. 

Note: parameters should be final, or else they would be breaking hashing rules

The main() function in Flutter is responsible for starting the program. Without the main() function, we cannot write any program in Flutter. The runApp function is responsible for returning the widgets attached to the screen as a root of the widget tree and will be rendered on the screen. 

The main() function came from Java-like languages so it's where all the programs have started, without it, we can't write any program on Flutter even without the UI. The runApp() function should return a widget that would be attached to the screen as a root of the widget Tree that will be rendered on the screen. We know that Flutter is a Framework, whereas Dart is a language.  

The main() function starts the execution of Dart Language, which in turn provides methods to load Flutter Components which is the runApp() method, which works as the main function for the Flutter Framework. In short, we can say that the main is the starting point of execution for Dart Language, and runApp() is the same for Flutter Framework. 

This question is a regular feature in Flutter interview, be ready to tackle it.  

The pubspec.yaml file, also known as 'pubspec', is included when we create a Flutter project and located at the top of the project tree. This file contains information about the dependencies like packages and their versions, fonts, etc., that a project requires. It makes sure that the next time when we build the project, we will get the same package version. Additionally, we can set constraints for the application.  

During working with the Flutter project or collaborating on a project, this configuration file of the project will be required a lot. This specification is written in YAML, which can be read by humans.  

The following are included in this file:  

  • General project settings, like name of the project, version, description, etc.  
  • Dependencies within a project.  
  • The assets of the project (e.g., images, audio, etc.). 

State management is one of the most important processes in the life cycle of an application. In Flutter, a state is whatever data we need to rebuild our UI at any moment in time. When this data changes, it will trigger a redraw of the user interface. The approaches for state management are as follows: 

  • setState: The low-level approach to use for widget-specific, ephemeral state. You can simply use Statefulwidget and setState() method to get the state. 
  • InheritedWidget & InheritedModel: It is another low-level approach used to communicate between ancestors and children in the widget tree. 
  • Provider: It is a wrapper around InheritedWidgets to make them more reusable and easier to use in our app. 
  • Riverpod: It is Reactive State-Management and Dependency Injection Framework with no dependency on Flutter. 
  • BloC: It makes it easy to implement the Business Logic Component design pattern, which separates presentation from business logic. 
  • GetIt: It is a service locator-based state management approach that doesn’t need a BuildContext. 
  • Mobx: MobX is a state-management library based on observables and reactions. 

This is a frequently asked question in Flutter advanced interview questions.  

ScopedModel in Flutter can be defined as a set of utilities that allows us to easily pass a data Model from a parent Widget straight down to its descendants. In addition, it also rebuilds all the children that use the model when the model is updated. This library was originally extracted from the Fuchsia codebase. The ScopedModel library consists of various utilities that allow the children’s UI elements to receive data from their parent widget. 

This library consists of three major classes as follows: 

  • ScopedModel – It can be used to wrap UI Components and access data from the Model. 
  • ScopedModelDescendant – It can be used to identify the correct ScopedModel from the widget hierarchy. 
  • The Model – We must extend the Model class to listen to the changes. 

For ScopedModel, we can give the example of Counter App and Todo app. 

Expect to come across this popular question in Flutter developer interview questions.  

The lifecycle of a stateful Widget explains the calling hierarchy of functions and it changes in the state of the widget. We know that everything in the Flutter is a widget. The Stateful and stateless are the types of widgets in Flutter. When Flutter builds a StatefulWidget, it creates a state object. This object is where all the mutable state for that widget is held. The concept of state is defined by two things.  

The data used by the widget might be changed. The data can't be read synchronously when the widget is built. (All state must be established by the time the build method is called). The Stateful widget lifecycle in Flutter has the following simplified steps in code. 

createState() 
mounted == true 
initState() 
didChangeDependencies() 
build() 
didUpdateWidget() 
setState() 
deactivate() 
dispose() 
mounted == false 

The Dart programming language has two types of optional parameters: named optional parameters and positional optional parameters. Dart's optional parameters are optional. In that, the caller isn't required to specify a value for the parameter while calling the function. Optional parameters can only be declared after any required parameters. The Optional parameters in Dart can have a default value, which is used when a caller does not specify a value. 

Positional optional parameters: - A parameter wrapped by [ ] is a positional optional parameter. Here is an example: 

Code: - 

getHttpUrl(String server, String path, [int port=80]) { 
  // ... 
} 

In the above code, the port is optional and has a default value of 80. We can call getHttpUrl with or without the third parameter. 

Code : - 

getHttpUrl('example.com', '/index.html', 8080); // here port = 8080 
getHttpUrl('example.com', '/index.html');       // here port = 80 

Named optional parameters : - A parameter wrapped by { } is a named optional parameter. Here is an example: 

Code : - 

getHttpUrl(String server, String path, {int port = 80}) { 
  // ... 
} 

We can call getHttpUrl with or without the third parameter. We must always use the parameter name while calling the function. Here is an example. 

Code : - 

getHttpUrl('example.com', '/index.html', port: 8080) ; // here port = 8080 
getHttpUrl('example.com', '/index.html') ;             // here port = 80 

We should always remember that you may use positional optional parameters or named optional parameters at a time, but not both in the same function or method. The phenomenon is not allowed. 

This constructor allows the Flutter developer to create a widget that displays on ImageStream obtained from the network. All the network images are cached regardless of the HTTP headers. An optional headers argument can be used to send custom HTTP headers with the image request. We make use of filterQuality to specify the rendering quality of image. The example is given below. 

Code: - 

Image.network(URL) // the URL is the URL of any image. 

The first step would be to import a simple library as given below: 

Code : - 

import ‘package:Flutter/foundation.dart’ as Foundation; 
Then, we can use kReleaseMode as shown below: - 

Code: - 

If(Foundation.kReleaseMode){ 
print(‘In release mode’); 
} else{ 
print(‘In debgugging mode’); 
} 

The asserts can be used to manually create an “is debug mode,” we should always avoid that. The issue with asserts is that the isInReleaseMode boolean value is not constant, so while shipping our application, both the dev as well as release mode codes are also shipped along with it. Over here the kReleaseMode is a constant, therefore the compiler can remove unused code correctly. 

Now we will see the Flutter interview question and answers for developers. These Flutter and dart interview questions can be asked to you if you are willing to join a company as a Flutter developer. 

I would make sure that I am making full use of all the features that are available in Flutter, by referring to the Flutter documentation and make use of different resources that are available online.

The Dart and Flutter provide us with tools, such as the http package, for this type of work. We can say the steps involved in making an HTTP request in Flutter are as follow:  

  • Step 1- Adding the http package.  
  • Step 2- Making a network request.  
  • Step 3- Converting the response into a custom Dart object.  
  • Step 4- Fetching the data.  
  • Step 5- Displaying the data.

JSON serialization with code generation means that having an external library that generates the encoding boilerplate for us. After some initial setup, we run a file watcher that generates the code from your model classes. For example, json_serializable and built_value are these kinds of libraries.  

This approach always scales well for a larger project. No hand-written boilerplate is needed for this, and typos when accessing the JSON fields are caught at compile time. The downside with code generation is that it requires some initial setup. Also, the generated source files might produce visual clutter in our project navigator. 

Dart apps function exclusively on a single thread by default. This technique frequently makes writing the code simpler and is quick enough to prevent poor app performance or stuttering animations. However, there are times when we might need to carry out an expensive calculation, such parsing a huge JSON document. The users will feel jank if this process takes more than 16 milliseconds.  

We must run costly computations like this in the background to prevent this jank. This means scheduling work for a different thread on Android. We can employ a different Isolate in Flutter. The following are the procedures for parsing JSON in Flutter:  

  • Step 1- Adding the http package.  
  • Step 2- Using the http package to send a network request.  
  • Step 3- Making the response into a gallery of images.  
  • Step 4- Transferring this project to a different isolation. 

In a normal constructor, an instance gets created and the final variables get instantiated with the initializer list, this is why there is no return statement. The instance to return is already fixed, when executing the constructor. In a factory constructor, the instance to return is decided by the method. That is why it needs a return statement and why it will usually call a normal constructor in at least one path.  

So, a factory does nothing different than a static method could do (in other languages often called getInstance()), except you cannot overload the constructor with a static method but you can with a factory method. i.e., factory methods are a way to hide the fact that the user of your class is not calling a constructor but a static method.  

For example: 

Code: - 

// named generative 
  // delegates to the default generative constructor 
  Person.greek(String name) : this(name, "Romania");  
 
  // named factory  
  factory Person.greek(String name) { 
    return Greek(name); 
  } 
} 
 
class Greek extends Person { 
  Greek(String name) : super(name, "Romania"); 
} 

The alignment property describes a point in the child's coordinate system and a different point in the coordinate system of this widget. The Align widget positions the child such that both points are lined up on top of each other. Contrarily, this is true of a column. A column's children are arranged vertically, top to bottom (by default).  

Since it has a vertical primary axis, this means that using crossAxisAlignment in a Column determines how the children are aligned horizontally in that Column whereas using mainAxisAlignment in a Column aligns its children vertically (for example, top, bottom). 

Flutter uses Keys for a lot of things inside the framework. Since our widget extends StatelessWidget or StatefulWidget, this is the way our widget having a key so that the framework knows what to do with it.  

The Keys allows widgets to change parents anywhere in our application without losing state, or they can also be used to access the information about another widget in a completely different part of the widget tree. So, the keys are not needed in a stateless widget but they are needed in a Stateful widget. 

A must-know for anyone heading into a Flutter interview, this question is frequently asked in Flutter interview questions for experienced.  

Flutter's profile mode compiles and launches our application identically to that of release mode but with just enough additional functionality to allow debugging performance problems. For example, profile mode provides tracing information to the profiling tools. We should use profile mode when we want to analyze the performance of our application.

I will use release mode for deploying my application when I want maximum optimization and minimal footprint size. Mostly, I would use release mode when I am ready to release my application.

Description

Tips for Preparing for Flutter Interview Questions

Now, that you have a good command of Flutter and Dart and are well-versed with the most asked interview question about Flutter, you should follow these certain tips to ace your next interview: 

  1. You should present yourself well in an interview, this is not Flutter/Dart related or related to your knowledge, but it’s very important. Most people are often hired for their good attitude, willingness to learn, and potential, especially if some technology is in its initial stage or is new, like Flutter. There are only a few true Flutter seniors now, so you should take full advantage of that.  
  2. You should also focus on polishing your CV according to market standards.  
  3. Put references to your previous work/experiences there. It would be best if you had some applications hosted on the Play Store or App Store, even the simplest one, so you could prove to the interviewer that you have gone through the entire process from creation to publishing and have hands-on experience with Flutter. 
  4. You should find out all you can about the company you’re going to the interview and have good knowledge about the tech stack mentioned in the job description. Remember, you have to convince the interviewer how you are beneficial to the organization. 
  5. Should have knowledge about the future plans of the company. 
  6. Before appearing for the interview, if it is a product-based company, you should try and understand the product of the company, it will help you to show the hiring manager that you are genuinely interested in the role. 

You should familiarize yourself with the STAR method to answer the questions: 

  1. Situation: Describe the scenario in sufficient detail so that the interviewer understands everything else in your response. 
  2. Task: Discuss specifically your role in this situation. 
  3. Action: Tell the interviewer what you did and why you did it. 
  4. Result: Tell the interviewer what happened and what you learned from this. 

How to Prepare for Flutter Developer Interview Questions?

Currently, there are 6000+ jobs for Flutter developers available just on LinkedIn. In the initial years, there were a few hundred jobs only. This is a huge expansion in such a short duration of time. Hence you should prepare well if you have your Flutter interview scheduled. You have to be prepared well for Flutter senior interview questions, too, along with keeping your basics clear. 

If you apply for the Flutter interview, you must know Dart programming language, at least at the beginner’s level, so you should first start from Dart Docs. Dart is a modern object-oriented programming language and if you are switching from Java or C++ or some similar OOP language, you would need a few weeks. 
After completing the Dart documentation, you shall thoroughly read the Flutter docs available online. It has many examples, best practices, and well documented features. You should focus on the most used widgets in this.  

Now that you know Flutter and Dart, you should do a couple of projects before sitting for the interviews and research the most asked Flutter Interview questions and answers and prepare them once. During your preparation time, you could learn a bunch of new stuff that would be especially useful in later stages, which would help you in becoming a good Flutter developer.  

The time that you invest in learning new stuff, especially in the area in which you are interested, is not wasted time. Many developers around the world are upskilling themselves with react native courses. Going for React Native course will help you get comprehensive hands-on with modern JS features. 

Job Roles for Flutter

  • Mobile Application Developer 
  • Flutter Application Developer 
  • Senior Mobile Application Developer 
  • Senior Flutter Developer 
  • Flutter Developer Intern 
  • Flutter Developer iOS/Android 
  • Flutter UI Developer 
  • Software Engineer- Mobile Apps 
  • Staff Mobile Engineer- Flutter 
  • Remote Flutter Developer 

Top Companies that Hire Flutter Developers

  • Google 
  • Amazon 
  • ByteDance 
  • Alibaba 
  • Dream11 
  • BMW 
  • Tencent 
  • eBay 
  • Groupon 

What to Expect in Flutter Interview Questions?

Before interviewing for a company as a Flutter developer, you should be well-prepared with Flutter interview questions and answers that are most likely to be asked. You should find all you can about the company you are going to the interview at; you should have a little knowledge about their future plans, etc. 

All of this will make you look like someone who cares about the company and is really interested in getting the job, which is especially important. In the interview, you shall ask questions, ask about the team, culture, expectations, roadmap, and technology.  

Remember, in every interview, you are presenting the interviewer with the whole of you, your personality, not just the developer part of yourself. Lastly, even if you are not selected after interviewing, it’s very important that you should never stop learning.  

You should always remember that the more you know about a technology, the more value you have on the job market. This is a very rapid environment that changes dynamically, and if you do not learn something almost every day, your value will decrease. Also, focus on improving yourself every day. 

Summary

Many industry experts believe Flutter will be the dominant mobile app soon because it has significant business benefits due to the support of cross-platform development. That is why businesses can now rapidly bring their products to market, saving costs and making them more accessible on more devices at the same time. The profit of the business increases manifolds due to this.  

Also, if you are planning a product where you only develop a native application to penetrate the market and then expand to the web platform once you have a stable financial condition and user base, Flutter is the ideal choice for you. Because of the single codebase used and the cross-platform functionality of Flutter, you can easily use the same code to expand your products at any time in the future.  

This can not only save your time and money; it also helps you to ensure that the user experience is seamless across all the platforms, because of such amazing features of Flutter, even many current tech giants like Google, Tencent, Hamilton, Alibaba, and many others of such elite organizations have built their mesmerizing user interface using the Flutter’s UI toolkit.  

Developing mobile apps at a rapid pace can be challenging for developers. Flutter, on the other hand, makes it a little bit easier. The Google Flutter SDK comes with plenty of free, open-source packages that make it easier for developers to build new apps quickly. Moreover, flutter itself is an open-source framework, so developers from all over the world can make their own additions to the library, this makes it easier to collaborate on the projects. To developers, Flutter is even more useful and easier to use, allowing faster app development.  

So, what is your favorite reason for using Flutter in your project? Most professionals skill up themselves with Mobile Development training. 

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