Flutter Interview Questions and Answers – Find Your Highly Qualified Developer

13 min read
Jun 07, 2021
Flutter Interview Questions and Answers – Find Your Highly Qualified Developer
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Asking the right Flutter technical interview questions of job candidates begins with a preliminary understanding of this tool as a software development platform. Indeed, as an employer who is going to interview candidates, you should have some technical idea of the development platform, and in this case, Flutter questions.

The introduction of Flutter by Google resulted in a huge competition in cross-platform application development. It is an open-source software development kit that allows developers to program applications for at least six platforms (Android, iOS, macOS, Windows, Linux, and Fuchsia) by operating from a single codebase. Although, its highest use case is in frontend (UI) mobile app development (Android and iOS).

As Flutter was released only in 2018 (the stable file; beta versions were released months before), there is an obvious skills gap for companies looking to migrate to Flutter to build their mobile apps. The situation is worsened by the fact that it is based on a whole new language (Dart). Therefore, it is difficult for most (potential) employers to find skilled Fluter developers that match their requirements.

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Fortunately, recruitment and outstaffing agencies are available to help. Outstaffing agencies, in particular, often have developers skilled in various platforms and languages available for hire. Even then, you, as the employer, need the right Flutter developer interview questions to determine if they are fit for the role.

So, how do you do that? This piece covers the top Flutter interview questions and answers for different experience levels. Read on to find out.

List of The Flutter Developer Interview Questions

The Flutter interview questions and answers are divided into junior, mid-level, and senior according to the expertise of the candidate in question.

Basic Level Flutter Developer Interview Questions Junior Developers

Flutter technical interview questions for junior developers are meant to cover the fundamental facts about the framework and the language (Dart) and how they work. Basically, you are trying to understand if the candidate has elementary knowledge of both.

Homer-is-a-trainee

Why is Flutter better than its competitors in mobile app development?

This should be a permanent fixture of any Flutter interview question and answer meeting, regardless of skill level. You need a developer who not only knows how to use Flutter but also believes in the platform’s possibilities as against its competitors in the mobile app development space.

  • Cross-platform development: Unlike other mobile app development tools such as Java and React Native that are built upon existing foundations, Flutter was developed from scratch and uses its own unique programming language, Dart. Moreover, its apps are compiled natively and so, building an app with it is far more seamless and requires less heavy coding.
one does not simply create two apps without Flutter
  • Flexible programming: The hot reload feature allows developers to modify code in real-time. This is very useful, particularly in debugging and testing. It is time-saving too since the app won’t have to restart to see changes.
  • Faster building process: Of course, Flutter is a cheaper tool for startups looking to develop one native app quickly for up to six operating systems, including the two major mobile platforms: Android and iOS. It is much easier to manage one app from a single codebase that works on six platforms than to manage six apps.

What are the advantages of Dart in programming?

Flutter supports two programming languages Dart and C++, but the former was specially created for use. Therefore, Flutter questions almost naturally always flow into the Dart space. Any Flutter developer must have at least basic understanding of Dart.

Unlike Python, Javascript, PHP, Ruby and etc., Dart uses static typing, which makes it type-safe and easier to detect and avoid runtime errors, as well as ensure effective code optimization overall.

dart night is comming

While Dart is fairly similar to Javascript, it runs code multiple times faster than the latter. The Dart VM (virtual machine) uses both Just-in-Time (JIT) and Ahead-of-Time (AOT) compilers to ensure faster and better code performance.

More so, Dart uses object-oriented programming, which makes it very scalable and stable for building even the most complex applications.

How do widgets work?

Flutter is known to heavily rely on widgets (like how React uses components). Every widget is used to execute a build() function and these units of composition make up the entire UI. Therefore, any set of Flutter technical interview questions that does not include widget-related inquiry is most probably not enough.

As its official documentation admits, almost everything is a widget, including layout models, images, and texts. Its layouts are built by assembling smaller widgets, each nested within a parent widget, to make bigger and more complex widgets.

flutter developer interview questions should always include something about widgets

Widgets serve a variety of aims including animation, input functionality, async functionality, interaction models, accessibility, scrolling, and style, among many others. Non-dynamic widgets like icons and labels are stateless widgets, while dynamic widgets such as Slider, TextField, Checkbox, etc. are stateful widgets.

What are some editors used in Flutter development?

The most popular Flutter IDEs include Android Studio, IntelliJ IDEA, Xcode, Emacs, Visual Studio, Codemagic, among others.

  • IntelliJ IDEA is feature-rich, boasts extensive support for many languages, and provides smart coding assistance. Most beginner developers would probably get by with the free Community Edition, but the paid Ultimate Edition is required to access additional features.
  • Android Studio works like IntelliJ IDEA but for Android only. Unlike the latter, though, Android studio is free and open-source. With smart coding assistance and a built-in debugger, it seems the best choice when programming for Android devices.
  • Visual Studio code, or simply VS Code, is a free tool backed by Microsoft. It speeds up development and lowers development time to minutes. It works with Windows, macOS, and Linux.

To add to this, you can also ask Flutter questions about what their favorite IDE is and justification for their choice.

Mid-Level Flutter Developer Interview Questions for Intermediate Developers

At mid-level, the Flutter interview question and answer flow should move away from the elementary and to the practical. You need the developer to demonstrate that they can work independently. Therefore, Flutter questions at this level should ask about concepts such as interactivity as well as elements and classes such as keys, build modes, and widget testing.

A guy is asking about difficult things

What are some drawbacks of Flutter and Dart?

Indeed Flutter is a great platform for mobile app development. However, a smart and competent developer must know the limits of their tools and be able to produce great results within those limits. Therefore, while Flutter interview questions and answers like this seem to be tricky at first, it is far from such.

Flutter, only just released in 2018, is still in the early stages, compared with established platforms such as native technology, Xamarin, and React Native. Therefore, it still needs time to have very rich library support.

Due to its rapid evolution, it can be a challenge for developers to maintain code because changes are being introduced and implemented constantly. On the one hand, it is indicative of growth; yet, on the other, it might make the job of developers more challenging.

Apps developed using Flutter are often storage-heavy. Native Java apps can be as small as 539 KB but for Flutter, the minimum is about 4 MB. Larger app sizes result in storage space issues and poor user experience for users.

joke about free up space for new app

How do you add interactivity to an app?

Stateful widgets are dynamic widgets that can be modified to respond to user input (interactivity). The state of a stateful widget can be managed by either the widget itself or the parent widget, or both. Aesthetic states are better managed by the widget while functional states (such as accepting user data), then the widget’s parent should manage such.

Alternatively, a developer may use the GestureDetector to implement interactivity for a custom widget in response to actions such as tapping and dragging.

How do you use keys?

The key class is a set of identifiers for Widgets, Elements, and SemanticsNodes. When widgets are modified within the widget tree, keys are responsible for preserving the state of those widgets. Collections of widgets that have an equivalent type and defined states can also be modified and reorganized using keys.

Otherwise, keys may be unnecessary to the code even though not detrimental in any way. Essentially, keys are useful when you have to modify a widget tree that contains stateful widgets but not when a tree is entirely composed of stateless widgets.

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What are the available build modes?

There are three build modes: Debug, Release, Profile. Each of the modes represents a stage in the development process.

The debug mode is used while the app is still in development and when you need to identify and remove existing and potential errors. Flutter’s hot reload feature allows you to do this in real-time and without needing to restart the software every time you make a change.

The release mode is used when the development process is complete and you are ready to deploy the app. To use the release mode, you need to disable debugging since it is assumed that an app ready for deployment must already be bug-free. The release mode optimizes compilation for fast execution.

flutter interview questions should cover it's productivity

The profile mode is used post-development. Every developer worth their salt knows that development does not end with app deployment. Therefore, in the profile mode, you still require some debugging functionality. Use this mode to analyze the real-time performance of your released app.

What is the BuildContext?

Widgets are created using the build method, whose functionality is, in turn, defined by a corresponding BuildContext argument. Basically, as its name implies, the BuildContext class defines the context of a custom-built widget.

Therefore, there is no widget without its own BuildContext as a reference to the widget’s location within the widget tree. BuildContext is commonly used to interact with a widget’s parents. You can also use BuildContext to access widget data easily.

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What is Widget Testing?

Basically, Flutter apps are subject to three main types of tests including unit tests and integration tests, as every competent developer must be familiar with. In Flutter, there is a third: widget test. Unit tests are for individual functions and elements while integration tests are comprehensive app tests.

However, widget tests are implemented for individual widgets. As everything in Flutter is a widget, familiarity with this type of testing is inevitable for successful development. In a non-Flutter framework, ‘widget testing’ would be the equivalent of ‘component testing’.

UnitWidgetIntegration
ConfidenceLowHigherHighest
Maintenance costLowHigherHighest
DependenciesFewMoreMost
Execution speedQuickQuickSlow

Tools for testing widgets include WidgetTester (for controlling widgets within the test environment), the testWidgets() function (for running callbacks in WidgetTester), Finder classes (for searching the widget tree during testing), and Matcher constants.

Advanced Level Flutter Developer Interview Questions for Senior Developers

The Flutter technical interview questions in this section are purely practical, for well obvious reasons. Ask senior candidates to explain difficult concepts such as state management and you may even venture into a discussion of the future of Flutter in development and business. A senior developer, by virtue of their experience, should also have foresight.

The Rock faced a challenge

Explain state management

This is easily one of the toughest concepts for developers to grasp on this platform. Therefore, asking a developer to explain state management is among the most telling Flutter interview questions and answers of the candidate’s true level of expertise.

For stateful widgets, a state is the local data that the widget holds that makes it respond to dynamic context, including interactive input. For the entire app, the state consists of everything contained in the app memory while running.

flutter state managment

There are two different types of state: app state and ephemeral state. First, the ephemeral state is the UI state. It is also called the local state because it is usually contained in a single widget. On the other hand, app state refers to a state that cuts across various parts of the app.

That is, it is not ephemeral. This includes shopping carts, user preferences, login info, and so on. Sometimes though, both the app state and the ephemeral state flow into each other that they are indistinguishable.

What are some approaches to state management?

  • setState is useful only for managing the ephemeral state; that is when the state is widget-specific. It is very straightforward and, in fact, it is not recommended to use a different approach for ephemeral state management.
  • InheritedWidget: as obvious from the name, this approach is used to manage data transmission between ancestors and children.
  • Redux: is useful for app state management and particularly for large, complex apps. Many web developers are already familiar with Redux and so using it in Flutter is not much of a hassle.
  • Other popular state management approaches include Provider, BLoC, MobX, Riverpod, and so on.
flutter interview questions help understand if the developer knows flutter

Explain the types of streams in Dart

Streams are a concept in asynchronous programming. They refer to the asynchronous sequence of data events within a program. The SteamController can be used to create new streams or manage existing ones. There are two main types of streams.

Single subscription streams are sequences contained within a larger whole. Such a stream only allows one listener throughout the sequence and the event is not triggered unless there is a listener. On the other hand, broadcast streams are versatile streams that allow more than one listener at a time. More so, one can listen again even a prior subscription has been canceled.

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What is the future of Flutter app development?

Besides the skills and the experience, you should expect your senior developers to be visionary. Flutter was only recently developed (in 2018) and if you are planning to develop an app, you need to be certain that there is a future for the platform. Therefore, you need a senior developer who not only can use Flutter but also believes it as a tool for the future so you can be assured that your investment would not go to drain.

There is no clear answer to this question since every developer would have diverse views and perspectives. However, you should watch out for answers that demonstrate ideas for overcoming the drawbacks of Flutter and how to make mobile app development better overall using this innovative SDK.

How to Prepare For a Flutter Interview Question and Answer Session as an Employer

While most of the Flutter technical interview questions here focus on hard skills, you should not neglect the role of soft skills in the development process. Flutter developers, at any level, still require soft skills such as communication skills, adaptability, teamwork, creativity, problem-solving, etc. to function properly.

There is a huge talent gap in the Flutter and Dart space. Therefore, you may not gain much from scouting Upwork, Fiverr, LinkedIn, Indeed, and the likes for Flutter developers who know Dart. Your best bet is to hire a software development agency that specializes in building Flutter app development teams, even if located offshore. Such is ProCoders. That way, you won’t even have to worry about your Flutter developers’ salaries.

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Tighten loose ends in the business aspect. Whichever engagement model you use, hiring developers is an important business process with legal implications. Therefore, make sure that there are no loose ends in the official agreement that you would present to the successful applicant(s).

Every Flutter interview question and answer session should not just be an avenue to quiz candidates. You should encourage the candidates to ask questions too. That means, you as an employer should be prepared to share your goals and expectations in the clearest manner in order to achieve mutual understanding.

An experienced guy

In essence, your Flutter interview question and answer session should not just feature technical inquiries. It should be an all-encompassing interaction between yourself and the candidate.

Conclusion

These Flutter interview questions and answers, and even more, feature during our own interview process for skilled developers that we include in teams we build for our clients. Therefore, there is no doubt that these Flutter questions would be useful to you too to reveal the strengths of your candidates.

Because Flutter is a relatively new platform and Dart has not attained the popularity of JavaScript, Python, and so on, it is not quite easy to find Flutter and Dart developers around or craft the right Flutter questions for them. That is why many companies outsource their development to software development companies abroad.

ProCoders, in Ukraine, is famed for some of the best developers around. ProCoders provides outstaffing software development services to companies from across the world. Developers at ProCoders offer just the right mix of skills and experience despite the scarcity of supply of Flutter developers. Therefore, by partnering with ProCoders, you can have a team ready for your app development project within days, all vetted to high standards and with proven experience and knowledge.

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