当值从 select 更改时不会触发 ngOnChanges

Question

我有下一个html:

<select  [(ngModel)]="district"  class="form-control" (change)="dsChange()">

      <option disabled hidden [value]="undefined" >Ноҳия</option>

      <option *ngFor="let dis of districts" [ngValue]="dis">{{dis.title}}</option>
</select>

我还有下一个组件

@Input() district: District;
 ngOnChanges(changes: SimpleChanges) {
      console.log("CHANGED")
}
 dsChange(){
      console.log(this.district);
}

而且我不明白为什么当我 select 一些值 dsChange 被正确的区值触发，但是 ngOnChanges() 不是

Answer 1

ngOnChanges 在组件的数据绑定输入属性更改时调用。在您的情况下，如果父组件为 @Input() district.

设置新值，则会调用它

See the docs

ngOnChanges()

Respond when Angular (re)sets data-bound input properties...Called before ngOnInit() and whenever one or more data-bound input properties change.

Answer 2

即使变量是 component.I 的本地变量，它也不会调用 onChanges 为此创建了一个 plukr:

https://plnkr.co/edit/lsqyeZ8aiBpylciOQxnU?p=preview

当值从 select 更改时不会触发 ngOnChanges

ngOnChanges is not triggered when value changes from select

angular2-template

ngonchanges

angular

ngOnChanges()