正如下面提供的代码.我试图选择由ngIf生成的动态元素但是失败了.
我总共用了两种方法.
> ElementRef和querySelector
组件模板:
`<div class="test" *ngIf="expr">
<a id="button">Value 1</a>
</div>
<div class="test" *ngIf="!expr">
<a id="button">Value 2</a>
</div>`
组件类:
expr: boolean;
constructor(
private elementRef: ElementRef,
) {
}
ngOnInit(): void{
//Call Ajax and set the value of this.expr based on the callback;
//if expr == true, then show text Value 1;
//if expr == false, then show text Value 2;
}
ngAfterViewInit(): void{
console.log(this.elementRef.nativeElement.querySelector('#button'));
}
输出结果为null.
> @ViewChild
组件模板:
`<div class="test" *ngIf="expr">
<a #button>Value 1</a>
</div>
<div class="test" *ngIf="!expr">
<a #button>Value 2</a>
</div>`
组件类:
@ViewChild('button') button: elementRef;
expr: boolean;
ngOnInit(): void{
//Call Ajax and set the value of this.expr based on the callback;
//if expr == true, then show text Value 1;
//if expr == false, then show text Value 2;
}
ngAfterViewInit(): void{
console.log(this.button);
}
输出结果未定义;
有没有办法获得* ngIf生成的动态dom?
最后,问题已经通过@ViewChildren解决了.
要记录更新的结果,必须使用单独的功能.
例如:
错误的代码:
@ViewChildren('button') buttons: ElementRef;
function(): void{
this.expr = true; // Change expression then the DOM will be changed;
console.log(this.buttons.toArray()); // This is wrong because you will still get the old result;
}
正确的代码:
@ViewChildren('button') buttons: ElementRef;
function(): void{
this.expr = true; // Change expression then the DOM will be changed;
}
ngAfterViewInit(): void{
this.buttons.changes.subscribe( e => console.log(this.buttons.toArray()) ); // This is right and you will get the latest result;
}
解决方法:
当* ngIf =“expr”表达式为false时,您无法获取该元素,因为该元素不存在.
仅当调用ngAfterViewInit()时,该值尚未在ngOnInit()中设置.
@Component({
selector: 'my-app',
template: `
<div class="test" *ngIf="prop">
<a #button id="button1">button1</a>
</div>
<div class="test" *ngIf="!boolean">
<a id="button2">button2</a>
</div>`
,
})
export class App {
@ViewChild('button') button: ElementRef;
prop:boolean = true;
ngAfterViewInit() {
console.log(this.button);
}
}
Plunker example with ViewChildren
@Component({
selector: 'my-app',
template: `
<button (click)="prop = !prop">toggle</button>
<div class="test" *ngIf="prop">
<a #button id="button1">button1</a>
</div>
<div class="test" *ngIf="!boolean">
<a #button id="button2">button2</a>
</div>`
,
})
export class App {
@ViewChildren('button') button: QueryList<ElementRef>;
prop:boolean = true;
ngAfterViewInit() {
console.log(this.button.toArray());
this.button.changes.subscribe(val => {
console.log(this.button.toArray());
});
}
}
原文地址:https://codeday.me/bug/20190519/1134217.html
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