Revealing Flutter Technical Interview Questions and Answers!

Ian Deed
Ian Deed
Published: 22.09.2022

Flutter is a UI development tool that is rapidly growing in popularity, appreciation, and use amongst developers. Capable of targeting multiple platforms with highly-performant code and a user-friendly UI — those familiar with Flutter have no question about what it can deliver for teams. In this guide, we've put together some Flutter technical interview questions (and answers) that can help you to identify the right skills and qualities in developers you intend to bring into your teams.

With strong Flutter skillsets in such high demand today, attracting and retaining these developers is as much about the culture and fit as the technical ability and practical skills they bring to your teams. One of our favorite technical guides to finding the right fit when it comes to a Flutter App Development company takes a deep dive into this topic to help you to create productive and lasting relationships with technology experts.

Of course, one of the unique difficulties of hiring and decision-making when it comes to Flutter is the very nature of such a unique technology solution. Technically speaking, Flutter is an SDK (software development kit) and not just a framework. This distinction that applies uniquely to Flutter introduces some complexity and nuance into the discussion amongst teams.

From Flutter's use of the dart language and Skia graphics engine for to the widget-based architecture and design — there's a lot to the discussion and use of Flutter that is unique only to the platform itself.

Two technical staff members shaking hands over a desk in a brightly lit office

Helpfully, we've created a handy technical primer for teams in our ultimate guide to Flutter. With a complete understanding of what Flutter is, what makes the technology work, and why it's so unique in the development landscape. Covering application development on Andriod, iOS, desktop and web development — our guide covers everything you need to begin asking the technical questions to help identify the right candidates for the role.

Flutter Technical Interview Questions (and answers)

Here, we've put together a series of technical questions that interest, challenge, and promote discussion amongst our Flutter teams. For the right candidates, these should do the same during your technical interview process and provide you with an insight into the skills and values of developers that you think you might hire.

If you're working on an app that requires experienced Flutter teams then take a look at our list of top Flutter development companies to find some of the best in the business today.

What are the advantages of using Flutter over Native development or another framework?

It's important that Flutter is chosen for a project for the right reasons and that developers can take full advantage of the unique characteristics of the technology. Look for the features of Flutter that matter most to a candidate and the advantages that they consider most important to a new development project.

Some of the key advantages that Flutter provides for candidates to draw on include:

  • Providing a performant and flexible UI architecture to developers. The ability to create exceptional user interfaces is one of the flagship features of Flutter and one of the key reasons teams choose it for their apps.
  • Enabling effective cross-platform development. The ability for Flutter apps to be deployed to Linux, macOS, Android, and windows amongst other platforms is key to reducing development and testing workloads when deploying a new application.
  • Creating a strong community to support projects. The resources and assistance available to developers embarking on using Flutter for the first time are some of the greatest strengths Flutter has against competing frameworks. There are an ever-increasing number of users and resources to get help from when stuck on projects.
  • Exceptional documentation provided by Google. Technical projects built and maintained by Google are well known amongst developers for providing excellent documentation and resources. There are few technical solutions as well-supported as Flutter is when it comes to tutorials and guides.
  • Achieving near-native application performance. When comparing Flutter to related mobile and cross-platform frameworks Google's platform has a distinct advantage in building its application directly to machine code. By not relying on an application bridge or intermediate solution Flutter unlocks remarkable performance credentials that are a close match for native applications.
  • Providing exceptional development tools. One of the distinct advantages Flutter application development has over native development is the tools and resources available to developers to support testing, speed-up development, and create better solutions. Tools such as live and hot reload are key examples that provide exceptional resources to speed-up development and debugging.
  • Flutter is being endorsed as the primary technology for developers to build applications on the Google Fuschia operating system.

What are some of the drawbacks of Flutter that can limit applications?

Knowing when you shouldn't use Flutter is just as important as knowing about its benefits. There are situations where you will almost certainly have to incorporate additional technologies and tools into an application to compensate for Flutter's drawbacks.

Some of the key limitations of Flutter include:

  • Limited third-party libraries are available for this relatively new platform running on Dart. Although this problem is becoming less significant over time it's still worth noting that JavaScript frameworks have a larger ecosystem to work with.
  • Reduced 3D rendering capabilities for modeling and games. Compared to frameworks designed to support gaming almost exclusively, Flutter's 3D graphics capabilities fall short of what some developers might expect. Integration for game engines such as unity is also severely lacking.
  • Increased app size compared to native or competing frameworks. As a result of bundling all of Flutter's resources and tools into the app to improve runtime performance and UI capabilities, the size of applications produced by Flutter is noticeably larger. As a result of this inflated app size, Flutter apps are often a poor choice for building instant apps for mobile app platforms.
  • Reliance on the Dart programming language. Google's Dart language is still relatively new in terms of software engineering tools. Having only grown in popularity since the release of Flutter in 2017, it's much younger than comparable languages such as Java which has more than 25 years of longevity. It can be difficult to find engineers and designers with the relevant experience as a result of using Dart.

What is the Container class?

A container is a widget with the capacity to house and manage multiple child widgets and their appearance. Widgets are often used in situations where design constraints apply to the position and appearance of the content being rendered on screen.

What’s the difference between stateless and stateful widgets?

In Flutter, Widgets are split into two categories: stateless and stateful.

A stateless widget handles no data. They are created once and don’t allow for stored variables to be changed. A stateful widget, in contrast, is more dynamic. Its values may update the UI and store values which influence the application in some way.

In the simplest possible terms: a user may manipulate a stateful widget such as an input field, text box, button, or slider.

Outline the lifecycle of a stateful Widget

The full widget lifecycle, in order, should feature:

  • createState() — A method called immediately on a stateful widget. The method should return a widget’s State object
  • initiate() — The first method called after the widget is created
  • didChangeDependencies() — Called the first time the widget is built and immediately after initState()
  • build() — Called only once in a stateless Widget. In a stateful Widget, it’s called every time the UI needs to render the widget. The method should return a widget’s tree
  • didUpdateWidget() — Called when there are changes to the parent widget changes the widget is forced to redraw its UI
  • deactivate() — Called when this object is removed from the tree
  • dispose() — Deallocates memory for the widget and its state

Two team members drawing a technical diagram of application design and architecture at a whiteboard

What are the two types of Flutter streams?

Streams are a core part of Dart functionality that Flutter relies on for its applications. The two types of Streams available to developers are:

  • Broadcast Streams. These streams allow multiple components to subscribe to events and listen simultaneously for changes. Broadcast streams don't guarantee delivery in a set sequence of events and will deliver events even when no subscribers are listening for them.
  • Single Subscription Stream. As the name implies, these streams can only be subscribed to by a single listener. The single subscription stream guarantees data is delivered sequentially to its subscriber and only triggers when there is a subscriber listening for events.

Finding Your Next Development Team Through Flutter Technical Interview

Flutter is a rapidly growing technology being used particularly often in mobile application development today. Yet, with the release of Flutter 3.0 earlier this year its use in desktop and web applications is only expected to grow from here. Reviewing these Flutter technical interview questions (and answers) can help give you an edge when it comes to demonstrating your skills and abilities to hiring managers.

Having a solid and robust technical grounding in the details of Flutter can help your teams to grow and target new areas of development with truly exceptional applications. Being able to answer these Flutter technical interview questions listed above with authority and interest is a strong sign the candidate you're interviewing has the technical ability and practical skillset you need to reach your audience.

FAQs:

Q1. How do I prepare for a Flutter interview?

You can prepare for a Flutter developer interview by brushing up on Flutter-specific technologies, general software developer problem-solving skills, and reviewing the technologies and tools you’ve worked with in the past for examples of where you've excelled and answers to some of the toughest technical questions.

The first place to look when preparing for a Flutter interview is the platform’s own documentation and releases. Analyze what’s new in the platform, what’s changed in recent months, and what interests you about the technology. Pay close attention to the details you think you could use for application development soon.

Next, take a look at the most popular and pressing questions that an interviewer is likely to ask. A simple Google search for ‘Flutter developer interview questions’ can bring up some of the most likely topics and help you to prepare answers that reflect your true skills and experience.

Finally, reviewing your portfolio and CV can help you present yourself well and demonstrate the technologies and tools you’ve previously used.

Q2. Is Flutter an SDK?

Yes, Flutter is an SDK (software development kit) that packages all the tools, resources, and software you need to produce applications. This is an area of Flutter that is often confused as many developers refer to Flutter as a framework.

In technology terms, a framework is a code structure that provides a starting architecture and some of the necessary tools to build an effective application. Flutter has this available to developers, but the Flutter framework is only a part of what makes it such a valuable tool for developers.

Packaged alongside Flutter's framework is a suite of code libraries for developers to use, APIs for code to interact with, and even a 2D graphics engine to render application components. It's the addition of these extra tools and resources that makes Flutter a complete SDK for developers. For simplicity and convenience, however, developers often abbreviate Flutter to being just a framework as that's how it's used and compared amongst many other tools.

Q3. What is hot restart in Flutter?

Hot restart is a Flutter tool that allows developers to rapidly restart an application in a development VM (virtual machine) to allow changes to take place without waiting for the entire application to be completely rebuilt.

Hot restart is often compared to hot reload as a related development tool that allows rapid iteration of code changes. Hot reload is a necessary tool for making small changes such as altering a single variable or making a slight UI alteration. The difference between the two tools comes from being saved in hot reload but destroyed during a hot restart.

In simple terms, a hot restart relaunches the app as if it's being started for the first time. The previous state is not saved and the app begins from its default state. Hot reload is slower than hot reload, but remains much much faster than a full application build and first-time startup.

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