Injectable

Compile-time metadata that marks a class Type or Function for injection.

The @Injectable() annotation has two valid uses:

1. On a class Type
2. On a top-level Function

Use #1: A class Type

The class must be one of the following:

• non-abstract with a public or default constructor
• abstract but with a factory constructor

A class annotated with @Injectable() can have only a single constructor or the default constructor. The DI framework resolves the dependencies and invokes the constructor with the resolved values.

Example

// Use the default constructor to create a new instance of MyService.
@Injectable()
class MyService {}
 
// Use the defined constructor to create a new instance of MyService.
//
// Each positional argument is treated as a dependency to be resolved.
@Injectable()
class MyService {
  MyService(Dependency1 d1, Dependency2 d2)
}
 
// Use the factory constructor to create a new instance of MyServiceImpl.
@Injectable()
abstract class MyService {
  factory MyService() => new MyServiceImpl();
}

Use #2: A top-level Function

The Injectable() annotation works with top-level functions when used with useFactory.

Example

// Could be put anywhere DI providers are allowed.
const Provide(MyService, useFactory: createMyService);
 
// A `Provide` may now use `createMyService` via `useFactory`.
@Injectable()
MyService createMyService(Dependency1 d1, Dependency2 d2) => ...