See also: Flutter's code of conduct
We gladly accept contributions via GitHub pull requests.
Please become familiar with our style guide and design philosophy. These guidelines are intended to keep the code consistent and avoid common pitfalls, and being familiar with them will make everything much easier for you. If you have questions about our processes or are looking for random tips and tricks, you may be interested in the engine wiki and framework wiki.
This document will introduce you to the basic steps for developing for the Flutter framework (Dart).
If you're interested in developing for the Flutter engine (C++, Java, Objective C), please
switch to the engine repo's CONTRIBUTING.md
document.
If you have an itch, work on that. If you are just looking for something good to start with, consider the issues marked "easy fix" in our issues list.
- Linux, Mac OS X, or Windows
- git (used for source version control).
- An IDE. We recommend Android Studio with the Flutter plugin.
- An ssh client (used to authenticate with GitHub).
- Python (used by some of our tools).
- The Android platform tools (see Issue #55
about downloading the Android platform tools automatically).
If you're also working on the Flutter engine, you can use the
copy of the Android platform tools in
.../engine/src/third_party/android_tools/sdk/platform-tools
.- Mac:
brew cask install android-platform-tools
- Linux:
sudo apt-get install android-tools-adb
- Mac:
- Ensure all the dependencies described in the previous section, in particular
git, ssh, and python are installed. Ensure that
adb
(from the Android platform tools) is in your path (e.g., thatwhich adb
prints sensible output). - Fork
https://github.com/flutter/flutter
into your own GitHub account. If you already have a fork, and are now installing a development environment on a new machine, make sure you've updated your fork so that you don't use stale configuration options from long ago. - If you haven't configured your machine with an SSH key that's known to github then follow the directions here: https://help.github.com/articles/generating-ssh-keys/.
git clone [email protected]:<your_name_here>/flutter.git
cd flutter
git remote add upstream [email protected]:flutter/flutter.git
(So that you fetch from the master repository, not your clone, when runninggit fetch
et al.)- Add this repository's
bin
directory to your path. That will let you use theflutter
command in this directory more easily. - Run
flutter update-packages
This will fetch all the Dart packages that Flutter depends on. You can replicate what this script does by runningpub get
in each directory that contains apubspec.yaml
file. - If you plan on using IntelliJ as your IDE, then also run
flutter ide-config --overwrite
to create all of the IntelliJ configuration files so you can open the main flutter directory as a project and run examples from within the IDE.
To run an example, switch to that example's directory, and use flutter run
.
Make sure you have an emulator running, or a device connected over USB and
debugging enabled on that device.
cd examples/hello_world
flutter run
You can also specify a particular Dart file to run if you want to run an example
that doesn't have a lib/main.dart
file using the -t
command-line option. For
example, to run the widgets/spinning_square.dart
example in the examples/layers
directory on a connected Android device, from that directory you would run:
flutter run -t widgets/spinning_square.dart
When running code from the examples directory, any changes you make to the
example code, as well as any changes to Dart code in the
packages/flutter directory and subdirectories, will
automatically be picked when you relaunch the app. You can do the same for your
own code by mimicking the pubspec.yaml
files in the examples
subdirectories.
When editing Flutter code, it's important to check the code with the
analyzer. There are two main ways to run it. In either case you will
want to run flutter update-packages
first, or you will get bogus
error messages about core classes like Offset from dart:ui
.
For a one-off, use flutter analyze --flutter-repo
. This uses the analysis_options.yaml
file
at the root of the repository for its configuration.
For continuous analysis, use flutter analyze --flutter-repo --watch
. This uses normal
analysis_options.yaml
files, and they can differ from package to package.
If you want to see how many members are missing dartdocs, you should use the first option,
providing the additional command --dartdocs
.
If you omit the --flutter-repo
option you may end up in a confusing state because that will
assume you want to check a single package and the flutter repository has several packages.
To automatically find all files named _test.dart
inside a package's test/
subdirectory, and
run them inside the flutter shell as a test, use the flutter test
command, e.g:
cd examples/stocks
flutter test
Individual tests can also be run directly, e.g. flutter test lib/my_app_test.dart
Flutter tests use package:flutter_test which provides flutter-specific extensions on top of package:test.
flutter test
runs tests inside the flutter shell. To debug tests in Observatory, use the --start-paused
option to start the test in a paused state and wait for connection from a debugger. This option lets you
set breakpoints before the test runs.
To run analysis and all the tests for the entire Flutter repository, the same way that Cirrus runs them, run dart dev/bots/test.dart
and dart dev/bots/analyze.dart
.
If you've built your own flutter engine, you
can pass --local-engine
to change what flutter shell flutter test
uses. For example,
if you built an engine in the out/host_debug_unopt
directory, you can pass
--local-engine=host_debug_unopt
to run the tests in that engine.
Flutter tests are headless, you won't see any UI. You can use
print
to generate console output or you can interact with the DartVM
via observatory at http://localhost:8181/.
To add a test to the Flutter package, create a file whose name
ends with _test.dart
in the packages/flutter/test
directory. The
test should have a main
function and use the flutter_test
package.
The flutter tool itself is built when you run flutter
for the first time and each time
you run flutter upgrade
. If you want to alter and re-test the tool's behavior itself,
locally commit your tool changes in git and the tool will be rebuilt from Dart sources
in packages/flutter_tools
the next time you run flutter
.
Alternatively, delete the bin/cache/flutter_tools.snapshot
file. Doing so will
force a rebuild of the tool from your local sources the next time you run flutter
.
flutter_tools' tests run inside the Dart command line VM rather than in the
flutter shell. To run the tests, ensure that no devices are connected,
then navigate to flutter_tools
and execute:
../../bin/cache/dart-sdk/bin/pub run test -j1
The pre-built flutter tool runs in release mode with the observatory off by default.
To enable debugging mode and the observatory on the flutter
tool, uncomment the
FLUTTER_TOOL_ARGS
line in the bin/flutter
shell script.
To start working on a patch:
git fetch upstream
git checkout upstream/master -b name_of_your_branch
- Hack away.
git commit -a -m "<your informative commit message>"
git push origin name_of_your_branch
To send us a pull request:
git pull-request
(if you are using Hub) or go tohttps://github.com/flutter/flutter
and click the "Compare & pull request" button
Please make sure all your checkins have detailed commit messages explaining the patch.
Once you've gotten an LGTM from a project maintainer and once your PR has received
the green light from all our automated testing (running on Cirrus, etc), and once
the tree is green (see the design principles
document for more details), submit your changes to the master
branch using one of
the following methods:
- Wait for one of the project maintainers to submit it for you.
- Click the green "Merge pull request" button on the GitHub UI of your pull request (requires commit access)
You must complete the Contributor License Agreement. You can do this online, and it only takes a minute. If you've never submitted code before, you must add your (or your organization's) name and contact info to the AUTHORS file.
We grant commit access to people who have gained our trust and demonstrated a commitment to Flutter.
We strive for a high degree of test coverage for the Flutter framework. We use Coveralls to track our test coverage. You can download our current coverage data from cloud storage and visualize it in Atom as follows:
- Install Atom.
- Install the lcov-info package for Atom.
- Open the
packages/flutter
folder in Atom. - Open a Dart file in the
lib
directory an typeCtrl+Alt+C
to bring up the coverage data.
If you don't see any coverage data, check that you have an lcov.info
file in
the packages/flutter/coverage
directory. It should have been downloaded by the
flutter update-packages
command you ran previously.
If you want to iterate quickly on improving test coverage, consider using this workflow:
- Open a file and observe that some line is untested.
- Write a test that exercises that line.
- Run
flutter test --merge-coverage path/to/your/test_test.dart
. - After the test passes, observe that the line is now tested.
This workflow merges the coverage data from this test run with the base coverage
data downloaded by flutter update-packages
.
See issue 4719 for ideas about how to improve this workflow.
You can work both with this repository (flutter.git) and the Flutter engine repository at the same time using the following steps.
-
Follow the instructions above for creating a working copy of this repository.
-
Follow the contributing instructions in the engine repository to create a working copy of the engine. The instructions also explain how to use a locally-built engine instead of the one bundled with your installation of the Flutter framework.
If you make a breaking change to the engine, you'll need to land your change in a few steps:
-
Land your change in the engine repository.
-
Publish a new version of the engine that contains your change. See the engine's release process for instructions about how to publish a new version of the engine. Publishing a new version is important in order to not break folks using prebuilt binaries in their workflow (e.g., our customers).
To view the API docs for the master
branch,
visit https://master-docs-flutter-io.firebaseapp.com/.
Those docs should be updated after a successful CI build
of Flutter's master
branch.
(Looking for the API docs for our releases? Please visit https://docs.flutter.io.)
We build and test Flutter on: