ioc_container 0.15.0

A Dart Ioc Container. Store and manage dependencies in one place keyed by type. It simplifies creating instances of your classes.

A Dart Ioc Container

ioc_container is a simple IoC Container for Dart and Flutter. You can use it for dependency injection or as a service locator. It has scoping and singleton support. If you've used Provider, you'll probably need an Ioc Container to compliment it. Provider and InheritedWidgets are good at passing dependencies through the widget tree, but Ioc Container is good at minting them in the first place. Return get<>() from your container to Provider's create builder method. Whenever Provider needs a dependency the Ioc Container will either create a new instance or grab one of the singletons/scoped objects. The library is so small that you can just copy the source code into Dartpad to share your code.

You can do this. It's nice.

final a = A('a');
final builder = IocContainerBuilder();
builder
  //Singletons last for the lifespan of the app
  ..addSingletonService(a)
  ..add((i) => B(i.get<A>()))
  ..add((i) => C(i.get<B>()))
  ..add((i) => D(i.get<B>(), i.get<C>()));
final container = builder.toContainer();
var d = container.get<D>();
expect(d.c.b.a, a);
expect(d.c.b.a.name, 'a');

Scoping

You can create a scoped container that will never create more than one instance of an object by type within the scope. You can check this example out in the tests. In this example, we create an instance of D but the object graph only has four object references. All instances of A, B, C, and D are the same instance. This is because the scoped container is only creating one instance of each type. When you are finished with the scoped instances, you can call dispose() to dispose everything.

final a = A('a');
final builder = IocContainerBuilder()
  ..addSingletonService(a)
  ..add((i) => B(i.get<A>()))
  ..add<C>(
    (i) => C(i.get<B>()),
    dispose: (c) => c.dispose(),
  )
  ..add<D>(
    (i) => D(i.get<B>(), i.get<C>()),
    dispose: (d) => d.dispose(),
  );
final container = builder.toContainer();
final scoped = container.scoped();
final d = scoped.get<D>();
scoped.dispose();
expect(d.disposed, true);
expect(d.c.disposed, true);

Async Initialization

You can do initialization work when instantiating an instance of your service. Just return a Future<T> instead of T (or use the async keyword). When you want an instance, call the init() method instead of get()

Warning: you must put error handling inside singleton or scoped async factories. If a singleton/scoped async factory throws an error, that factory will continue to return a Future with an error for the rest of the lifespan of the container.

  test('Test Async', () async {
    final builder = IocContainerBuilder()
      ..add(
        (c) => Future<A>.delayed(
          //Simulate doing some async work
          const Duration(milliseconds: 10),
          () => A('a'),
        ),
      )
      ..add(
        (c) => Future<B>.delayed(
          //Simulate doing some async work
          const Duration(milliseconds: 10),
          () async => B(await c.init<A>()),
        ),
      );

    final container = builder.toContainer();
    final b = await container.init<B>();
    expect(b, isA<B>());
    expect(b.a, isA<A>());
  });

As a Service Locator

You can use an IocContainer as a service locator in Flutter and Dart. Just put an instance in a global space and use it to get your dependencies anywhere with scoping.

Note: there are many ways to avoid declaring the container globally. You should weigh up your options and make sure that declaring the container globally is the right choice for your app.

late final IocContainer container;

void main(List<String> arguments) {
  final builder = IocContainerBuilder()
    ..addSingletonService(A('A nice instance of A'))
    ..add((i) => B(i.get<A>()))
    ..add((i) => C(i.get<B>()))
    ..add((i) => D(i.get<B>(), i.get<C>()));
  container = builder.toContainer();

  final d = container.scoped().get<D>();
  // ignore: avoid_print
  print('Hello world: ${d.c.b.a.name}');
}

Install it like this:

dart pub add ioc_container