How to use packages
The Dart ecosystem uses packages to manage shared software such as libraries and tools. To get Dart packages, you use the pub package manager. You can find publicly available packages on the pub.dev site, or you can load packages from the local file system or elsewhere, such as Git repositories. Wherever your packages come from, pub manages version dependencies, helping you get package versions that work with each other and with your SDK version.
At a minimum, a Dart package is a directory containing a pubspec file. The pubspec contains some metadata about the package. Additionally, a package can contain dependencies (listed in the pubspec), Dart libraries, apps, resources, tests, images, and examples.
To use a package, do the following:
- Create a pubspec (a file named
pubspec.yamlthat lists package dependencies and includes other metadata, such as a version number).
dart pub getto retrieve your package's dependencies.
- If your Dart code depends on a library in the package, import the library.
Creating a pubspec#
The pubspec is a file named
pubspec.yaml that's in the top directory of your application. The simplest possible pubspec lists only the package name:
Here is an example of a pubspec that declares dependencies on two packages (
intl) that are hosted on the pub.dev site:
To update the
pubspec.yaml file, without manual editing, you can run
dart pub add command. The following example adds a dependency on
$ dart pub add vector_math
+ vector_math 2.1.3
Downloading vector_math 2.1.3...
Changed 1 dependency!
For details on creating a pubspec, see the pubspec documentation and the documentation for the packages that you want to use.
Once you have a pubspec, you can run
dart pub get from the top directory of your application:
$ cd <path-to-my_app>
$ dart pub get
This process is called getting the dependencies.
dart pub get command determines which packages your app depends on, and puts them in a central system cache. If your app depends on a published package, pub downloads that package from the pub.dev site. For a Git dependency, pub clones the Git repository. Transitive dependencies are included, too. For example, if the
js package depends on the
pub grabs both the
js package and the
Pub creates a
package_config.json file (under the
.dart_tool/ directory) that maps each package name that your app depends on to the corresponding package in the system cache.
Importing libraries from packages#
To import libraries found in packages, use the
import 'package:js/js.dart' as js;
The Dart runtime takes everything after
package: and looks it up within the
package_config.json file for your app.
You can also use this style to import libraries from within your own package. Let's say that the
transmogrify package is laid out as follows:
parser_test.dart file can import
parser.dart like this:
Upgrading a dependency#
The first time you get a new dependency for your package, pub downloads the latest version of it that's compatible with your other dependencies. It then locks your package to always use that version by creating a lockfile. This is a file named
pubspec.lock that pub creates and stores next to your pubspec. It lists the specific versions of each dependency (immediate and transitive) that your package uses.
If your package is an application package you should check this file into source control. That way, everyone working on your app uses the same versions of all of its dependencies. Checking in the lockfile also ensures that your deployed app uses the same versions of code.
When you're ready to upgrade your dependencies to the latest versions, use the
dart pub upgrade command:
$ dart pub upgrade
dart pub upgrade command tells pub to regenerate the lockfile, using the newest available versions of your package's dependencies. If you want to upgrade only one dependency, you can specify the package to upgrade:
$ dart pub upgrade transmogrify
That command upgrades
transmogrify to the latest version but leaves everything else the same.
dart pub upgrade command can't always upgrade every package to its latest version, due to conflicting version constraints in the pubspec. To identify out-of-date packages that require editing the pubspec, use
dart pub outdated.
The following pages have more information about packages and the pub package manager.
- Pub dependencies
- Pub environment variables
- Pub glossary
- Pub package layout conventions
- Pub versioning philosophy
- Pubspec format
dart pub tool provides the following subcommands:
For an overview of all the
dart pub subcommands, see the pub tool documentation.
Troubleshooting pub gives solutions to problems that you might encounter when using pub.