Host

decorator

Contents

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.

Description

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

Options

Usage notes

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 {
}