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Installation

Setting up inject.dart involves adding three packages and running the code generator. This chapter walks through each step.

Packages

PackageRoleDependency type
inject_annotationAnnotations your code uses (@inject, @provides, …)regular
inject_generatorCode generator — reads annotations, emits .inject.dartdev
build_runnerDart’s standard build system; runs the generatordev
inject_flutterViewModelFactory<T> and ViewModelBuilder<T> for Flutterregular

inject_annotation is the only package that ships with your app. inject_generator and build_runner are dev dependencies — they are not included in the production build.

inject_flutter is optional; add it only in Flutter projects that use the ViewModelFactory<T> pattern.

Adding Dependencies

Flutter projects

flutter pub add inject_annotation inject_flutter
flutter pub add --dev inject_generator build_runner

Or in a single command:

flutter pub add inject_annotation inject_flutter dev:inject_generator dev:build_runner

Dart-only projects (no Flutter integration)

dart pub add inject_annotation dev:inject_generator dev:build_runner

Running the Code Generator

After annotating your classes, generate the wiring code:

dart run build_runner build

This processes every file with inject.dart annotations. It writes a .inject.dart library next to each @Component, and a .factory.dart part next to each file that declares an @assistedInject (or @assistedFactory) constructor.

If output files from a previous run conflict, add --delete-conflicting-outputs:

dart run build_runner build --delete-conflicting-outputs

Watch Mode

build_runner can watch for file changes and regenerate automatically:

dart run build_runner watch

Watch mode is convenient during development, but keep in mind:

  • It holds a background process that can use significant CPU/memory in large projects.
  • Many developers prefer explicit rebuilds — run build_runner build once when a batch of changes is complete.
  • IDEs with Flutter/Dart tooling often provide a UI button that runs the build command for you.

Verifying the Setup

After the first successful build you will see files like:

lib/main.inject.dart
lib/src/features/home/home_page.factory.dart
lib/src/features/app/my_app.factory.dart

These are generated — never edit them by hand. They are typically git-ignored at the package level (add *.inject.dart and *.factory.dart to .gitignore), with the documented exception of the pub.dev example where they are committed so the snapshot is self-contained.

If you see an error such as Bad state: component class must declare at least one @inject-annotated provider, see the Quickstart chapter’s Troubleshooting section.