我试图在我的两个组件(父组件和子组件)之间使用双向绑定,并尝试在两个组件的ngOnChanges中检测由此引起的更改 . 我可以通过更改父组件(App Component)的输入/输出属性来触发子组件(测试组件)的ngOnChanges . 但是,我无法通过更改Child组件中的双向绑定属性来触发Parent组件的ngOnChanges .
可以在这里找到Working Plunker:https://plnkr.co/edit/AGh6EM9l9ENMufb9JWPW?p=preview
import { Component, OnInit, OnChange, Output, Input, EventEmitter } from '@angular/core';
@Component({
selector: 'my-app',
template: `<h1>Hello {{name}}</h1>
<h3>Two Way Parent - {{twoWaySend}} </h3>
<button (click) = "oneWayButtonPressed()">Increase oneWay from Parent</button>
<button (click) = "twoWayButtonPressed()">Increase TwoWay from Parent</button>
<test-component [oneWayReceive] = 'oneWaySend'
[(twoWayReceive)] = 'twoWaySend'></test-component>`
})
export class AppComponent implements OnChanges{
name = 'Angular';
oneWaySend = "You shall pass";
twoWaySend = "You shall both ways";
counter:int = 0;
negativeCounter:int = 0;
oneWayButtonPressed() {
this.oneWaySend = `${this.oneWaySend} ${++this.counter}`;
}
twoWayButtonPressed() {
this.twoWaySend = `${this.twoWaySend} ${--this.negativeCounter}`;
}
ngOnChanges() {
console.log('ngOnchange Parent ' + this.twoWaySend);
}
}
@Component({
selector: 'test-component',
template: `<h1>TestComponent {{name}} {{oneWayReceive}}</h1>
<h3>Two Way Child - {{twoWayReceive}}</h3>
<button (click) = "twoWayButtonPressed()">Change Two Way from Child</button>`
})
export class TestComponent implements OnChange {
@Input() oneWayReceive;
@Input() twoWayReceive;
@Output() twoWayReceiveChange: EventEmitter<string> = new EventEmitter<string>();
name = 'Angular';
negativeCounter = 0;
ngOnChanges() {
console.log(`OneWayReceive ${this.oneWayReceive} TwoWayReceive ${this.twoWayReceive}`);
}
twoWayButtonPressed() {
this.twoWayReceive = `${--this.negativeCounter} ${this.twoWayReceive}`;
this.twoWayReceiveChange.emit(this.twoWayReceive);
}
}
3 回答
仅当父组件为组件的输入传递不同的值时,才会调用
ngOnChanges
. 你不应该调用't expect the parent component' sngOnChanges
方法,因为它没有任何输入,也没有任何父组件 .简直就是你不能
您只能从父级到子级检测到,如果要将更改的值或事件从子级传递给父级,则必须使用
@Outpput
或EventTrigger via Service
Angular文档声明,
ngOnChanges
被调用:如果要捕获此更新;
您可以显式使用输出/事件绑定,而不是使用
[()]
.[twoWayReceive]="twoWaySend" (twoWayReceiveChange)="twoWaySendChange($event)"
父组件中的输出更改处理程序将是