为何在Angular 4 @Directive中初始化组件时调用ngModel.valueChanges

Question

我有一个指令观察组件更改，并在更改值时调用自定义验证器。

为什么ngModel.valueChanges在初始化组件时有新的变化？

@Directive({
    providers: [NgModel],
    selector: "[inputValidator][ngModel]",
})
@Inject(BootstrapFormGroupComponent)
export class InputValidatorDirective implements OnInit, BootstrapFormGroupMember {

  public ngOnInit() {
    this.ngModel.valueChanges.subscribe((value) => {
        // ...
        // calling custom validators
        // why it is called after the component has initialized
        // ...
    });
  }

}

HTML：

<input type="number" inputValidator [validator]="postalCodeValidator" [(ngModel)]="postalCode" class="form-control" />

Answer 1

我在角度6中面临同样的问题，我能找到的唯一解决方案是使用像这样的skip（1）

    this.ngModel.valueChanges.pipe(skip(1)).subscribe((value) => {
        // your code here
    });