Host
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.
说明
For an extended example, see "Dependency Injection Guide".
使用说明
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 {
}
