Host

decorator

A parameter decorator on a view-provider parameter of a class constructor that tells the DI framework to resolve the view by checking injectors of child elements, and stop when reaching the host element of the current component.

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说明

For an extended example, see "Dependency Injection Guide".

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The following shows use with the @Optional decorator, and allows for a null result.

      
      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 {
}

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