What does Flutter do?

Flutter gives developers an easy and productive way to build and deploy cross-platform, high-performance mobile apps on both Android and iOS.

Flutter gives users beautiful, fast, and jitter-free app experiences.

What does Flutter provide?

Flutter has four main components:

  • a heavily optimized, mobile-first 2D rendering engine (with excellent support for text)
  • a functional-reactive framework (optional, you can bring-your-own framework)
  • a set of Material Design widgets (optional, you can bring-your-own widgets)
  • command-line tools and plugins for IntelliJ IDEA, including the free Community edition.

What makes Flutter unique?

Flutter is different than most other options for building cross-platform mobile apps because Flutter uses neither WebView nor the OEM widgets that shipped with the device. Instead, Flutter uses its own high-performance rendering engine to draw widgets.

Flutter also offers developers a highly productive and fast development experience, fast runtime and engine performance, and beautifully designed widgets that make for beautiful apps.

Why would I want to invest in learning Flutter?

Flutter is an easy way to use a single codebase to deliver beautiful mobile apps that run on both Android and iOS. Flutter gives developers quick edit/debug cycles for an enjoyable low-friction workflow.

What are Flutter’s guiding principles?

We believe that:

  • In order to reach every potential user, developers need to target multiple mobile platforms.
  • HTML and WebViews as they exist today make it challenging to consistently hit high frame rates and deliver high-fidelity experiences, due to automatic behavior (scrolling, layout) and legacy support.
  • Today, it’s too costly to build the same app multiple times: it requires different teams, different code bases, different workflows, different tools, etc.
  • Developers want an easier, better way to use a single codebase to build mobile apps for multiple target platforms, and they don’t want to sacrifice quality, control, or performance.

We are focused on three things:

  • Control - Developers deserve access to, and control over, all layers of the system. Which leads to:
  • Performance - Users deserve perfectly fluid, responsive, jank-free apps. Which leads to:
  • Fidelity - Everyone deserves precise, beautiful, delightful mobile app experiences.

Sky was the codename of an earlier version of Flutter.

What devices and OS versions does Flutter run on?

Mobile operating systems: Android Jelly Bean, v16, 4.1.x or newer, and iOS 8 or newer.

Mobile hardware: 64-bit iOS devices (starting with iPhone 5S and newer iPhone models), and ARM Android devices.

We support developing Flutter apps with Android and iOS devices, as well as with Android emulators and the iOS simulator.

We test on a variety of low-end to high-end phones (excluding tablets) but we don’t yet have an official device compatibility guarantee. We do not offer support for tablets or have tablet-aware layouts.

What technology is Flutter built with?

Flutter is built with C, C++, Dart, and Skia (a 2D rendering engine). See this architecture diagram for a better picture of the main components.

How does Flutter run my code on Android?

The engine’s C/C++ code is compiled with Android’s NDK, and the majority of the framework and application code is running as native code compiled by the Dart compiler.

How does Flutter run my code on iOS?

The engine’s C/C++ code is compiled with LLVM, and any Dart code is AOT-compiled into native code. The app runs using the native instruction set (no interpreter is involved).

Does Flutter run on the web?

No. We do not plan to provide a web version of Flutter.

What operating systems can I use to build a Flutter app?

Flutter supports development on Linux, Mac, and, Windows.

What kinds of apps can I build with Flutter?

Flutter is optimized for 2D mobile apps that want to run on both Android and iOS. Apps that use Material Design are particularly well suited for Flutter.

What kind of app performance can I expect?

You can expect excellent performance. Flutter is designed to help developers easily achieve a constant 60fps. Flutter apps run via natively compiled code – no interpreters are involved.

Can I use Flutter to build desktop apps?

We are focused on mobile-first use cases. However, Flutter is open source and we encourage the community to use Flutter in a variety of interesting ways.

Can I use Flutter inside of my existing native app?

Yes, you can embed a Flutter view in your existing Android or iOS app. You can learn more about this at [[docs coming soon]]. If you want to do this, we encourage you to email our mailing list: flutter-dev@googlegroups.com.

Can I access platform services and APIs like sensors and local storage?

Yes. Flutter gives developers out-of-the-box access to some platform-specific services and APIs from the operating system. However, we want to avoid the “lowest common denominator” problem with most cross-platform APIs, so we do not intend to build cross-platform APIs for all native services and APIs.

We encourage developers to use Flutter’s asynchronous message passing system to create your own integrations with platform and third-party APIs. Developers can expose as much or as little of the platform APIs as they need, and build layers of abstractions that are a best fit for their project.

Can I interop with my mobile platform’s default programming language?

Yes, Flutter supports calling into the platform, including integrating with Java code on Android, and ObjectiveC or Swift code on iOS. This is enabled via a flexible message passing style where a Flutter app may send and receive messages to the mobile platform using a BasicMessageChannel.

Learn more about accessing platform and third-party services in Flutter.

Here is an example project that shows how to use a platform channel to access battery state information on iOS and Android.

Does Flutter come with a framework?

Yes! Flutter ships with a functional-reactive style framework, inspired by React. However, Flutter’s framework is designed to be optional and layered. Developers can choose to use only parts of the framework, or a different framework.

Does Flutter come with widgets?

Yes! Flutter ships with a set of high quality Material and Cupertino (iOS-styled) widgets, layouts, and themes. You can see a collection of those widgets. Of course, these widgets are optional. Flutter is designed to make it easy to create your own widgets, or customize the existing widgets.

Why does Flutter not use the host platform’s native widgets?

We are hoping the end-result will be higher quality apps. If we reused the OEM widgets, the quality and performance of Flutter apps would be limited by the quality of those widgets.

In Android, for example, there’s a hard-coded set of gestures and fixed rules for disambiguating them. In Flutter, you can write your own gesture recognizer that is a first-class participant in the gesture system. Moreover, two widgets authored by different people can coordinate to disambiguate gestures.

Can I extend and customize the bundled widgets?

Absolutely. Flutter’s widget system was designed to be easily customizable. You can see an example of that at [[docs coming soon]].

Does Flutter come with a testing framework?

Flutter apps are tested with the test package. Learn more about testing with Flutter.

Does Flutter come with a dependency injection framework or solution?

Not at this time. Please share your ideas at flutter-dev@googlegroups.com.

Does Flutter come with a reflection/mirrors system?

Not at this time. Because Flutter apps are pre-compiled for iOS, and binary size is always a concern with mobile apps, we disabled dart:mirrors. We are curious what you might need reflection/mirrors for – please let us know at flutter-dev@googlegroups.com.

How do I do internationalization (i18n), localization (l10n), and accessibility (a11y) in Flutter?

Flutter has basic support for accessibility on iOS and Android, though this feature is a work in progress.

Flutter developers are encouraged to use the intl package for internationalization and localization.

We encourage you to email flutter-dev@googlegroups.com with your questions regarding these features.

How do I write parallel and/or concurrent apps for Flutter?

Flutter supports isolates. Isolates are separate heaps in Flutter’s VM, and they are able to run in parallel (usually implemented as separate threads). Isolates communicate by sending and receiving asynchronous messages. Flutter does not currently have a shared-memory parallelism solution, although we are evaluating solutions for this.

Check out an example of using isolates with Flutter.

Can I use JSON/XML/protobuffers/etc with Flutter?

Absolutely. There are libraries in pub.dartlang.org for JSON, XML, protobufs, and many other utilities and formats.

How do I write well-styled code for Flutter?

The code in the flutter repos follow our opinionated style guide.

Developers are not required to use this style guide for their own app code, though.

Does Flutter use my system’s OEM widgets?

No. Flutter provides a set of Material Design widgets, managed and rendered by Flutter’s framework and engine.

How do I deploy a Flutter app?

Flutter apps are most commonly deployed via the mobile platform’s store (such as Apple’s App Store and Google’s Play Store).

Our command-line tools can build an .ipa and .apk file for you. To learn more, run flutter build --help.

What if I don’t want to build my app with Material Design?

Flutter’s widget system is designed to be extensible, and it’s supported and possible to create your own set of widgets using our base classes.

Does Flutter work with any editors or IDEs?

We are building plugins for IntelliJ IDEA, enabling fully integrated development experience for Flutter. The plugins work in both the Ultimate and the free Community editions.

Alternatively, you can use a combination of the flutter command in a terminal and one of the many editors that support editing Dart.

Can I build 3D (OpenGL) apps with Flutter?

Today we don’t support for 3D via OpenGL ES or similar. We have long-term plans to expose an optimized 3D API, but right now we’re focused on 2D.

How big is the Flutter engine?

In November 2015, we measured the size of a minimal Flutter app, bundled as an APK, to be approximately 8MB. For this simple app that used Material Design widgets, the core engine is approximately 5MB, the framework + app code is approximately 400kb, necessary Java code is 330k, and there is approximately 2.5MB of ICU data. We are working to get this smaller.

My app has a Slow Mode banner/ribbon in the upper right. Why am I seeing that?

By default flutter run command uses the debug build configuration. The debug configuration enables type checking and asserts. These checks help you catch errors early during development but impose a runtime cost. The “slow mode” banner indicates that these checks are enabled. You can run your app without these checks by using either --profile or --release flag to flutter run.

If you are using the Flutter plugin for IntelliJ, please note that it currently does not support running in --profile or --release modes (see issue #410).

Where can I get support?

If you think you’ve encountered a bug, please file it in our issue tracker. We encourage you to use Stack Overflow for “HOWTO” type questions. For discussions, please join our mailing list at flutter-dev@googlegroups.com.

How do I get involved?

Flutter is open source, and we encourage you to contribute. You can start by simply filing issues for feature requests and bugs in our issue tracker. You should also join our mailing list at flutter-dev@googlegroups.com and let us know how you’re using Flutter and what you’d like to do with it. If you’re interested in contributing code, you can start by reading our Contributing guide.

Should I build my next production app with Flutter?

Flutter is still being developed and is not yet at 1.0. While lower levels of the system are stabilizing, we continue to improve parts of the system based on user feedback.

Flutter is used inside of Google, but those apps are not yet deployed to external users.

So really, it is up to you. Please let us know if you released an app built with Flutter to users. We’d love to hear what you’re building!

I heard Apple rejects apps built with third-party frameworks, is that true? Will Apple reject my Flutter app?

We can’t speak for Apple, but Apple’s policies have changed, and they have allowed apps built with systems like Flutter. Of course, Apple is ultimately in charge of their ecosystem, but our goal is to continue to do everything we can to ensure Flutter apps can be deployed into Apple’s App Store.

What language is Flutter written in?

We looked at a lot of languages and runtimes, and ultimately adopted Dart for the framework and widgets. The underlying graphics framework and the Dart virtual machine are implemented in C/C++.

Why did Flutter choose to use Dart?

The primary criteria we used to pick a programming language were the following:

  • Developer productivity. One of Flutter’s main value propositions is that it saves engineering resources by letting developers create apps for both iOS and Android with the same codebase. Using a highly productive language accelerates developers further and makes Flutter more attractive.

  • Object-orientation. For Flutter, we want a language that’s suited to Flutter’s problem domain: creating visual user experiences. The industry has multiple decades of experience building user interface frameworks in object-oriented languages. While we could use a non-object-oriented language, this would mean reinventing the wheel to solve several hard problems.

  • Predictable, high performance. With Flutter, we want to empower developers to create fast, fluid user experiences. In order to achieve that, we need to be able to run a significant amount of end-developer code during every animation frame. That means we need a language that both delivers high performance and delivers predictable performance, without periodic pauses that would cause dropped frames.

  • Fast allocation. The Flutter framework uses a functional-reactive style programming model, whose performance depends heavily on the underlying memory allocator efficiently handling small, short-lived allocations. The functional-reactive style was developed in languages with this property and does not work efficiently in languages that lack this facility.

Dart scores highly on all four dimensions. In addition, we have the opportunity to work closely with the Dart community, which is actively investing resources in improving Dart for use in Flutter. For example, when we adopted Dart, the language did not have an ahead-of-time toolchain for producing native binaries, which is instrumental in achieving predictable, high performance, but now the language does because the Dart team built it for Flutter. Similarly, the Dart VM has previously been optimized for throughput but the team is now optimizing the VM for latency, which is more important for Flutter’s workload.

Can Flutter run any Dart code?

Flutter should be able to run most Dart code that does not import (transitively, or directly) dart:mirrors or dart:html.

Why is the build() method on State, not StatefulWidget?

Putting a Widget build(BuildContext context) method on State rather putting a Widget build(BuildContext context, State state) method on StatefulWidget gives developers more flexibility when subclassing StatefulWidget. You can read a more detailed discussion on the API docs for State.build.

Which software license(s) apply to Flutter and its dependencies?

Flutter includes two components: an engine that ships as a dynamically linked binary, and the Dart framework as a separate binary that the engine loads. The engine uses multiple software components with many dependencies; view the complete list here.

The framework is entirely self-contained and requires only one license.

In addition, any Dart packages you use may have their own license requirements.

How can I determine the licenses my Flutter application needs to show?

There’s an API to find the list of licenses you need to show:

Who works on Flutter?

Flutter is an open source project. Currently, the bulk of the development is done by engineers at Google. If you’re excited about Flutter, we encourage you to join the community and contribute to Flutter!