Specifies that an injector should retrieve a dependency from any injector until reaching the host element of the current component.

How to use

@Injectable() class Car { constructor(@Host() public engine:Engine) {} }

Description

For more details, see the Dependency Injection Guide.
Example

class OtherService {}

class HostService {}

@Directive({selector: 'child-directive'})

class ChildDirective {

 logs: string[] = [];

 constructor(@Optional() @Host() os: OtherService, @Optional() @Host() hs: HostService) {

 // os is null: true

 this.logs.push(`os is null: ${os === null}`);

 // hs is an instance of HostService: true

 this.logs.push(`hs is an instance of HostService: ${hs instanceof HostService}`);

 }

}

@Component({

 selector: 'parent-cmp',

 viewProviders: [HostService],

 template: '<child-directive></child-directive>',

})

class ParentCmp {

}

@Component({

 selector: 'app',

 viewProviders: [OtherService],

 template: '<parent-cmp></parent-cmp>',

})

class App {

}

//parentservice 是child的host，再上层就不是了