由于$digest
- 循环检查所有内容,我试图解决AngularJS中不存在的问题。
我试图创建一个可以初始化自身(异步)的组件,并通知其周围的容器已完成加载。
我有这个伪表:
<my-table>
<ng-container *ngFor="let row in rows">
<my-table-row
[row]="row"
[isLoading]="row.isLoading"
(click)="onClickRow(row)"
></my-table-row>
<my-detail-row *ngIf="row.isExpanded">
<my-component
[data]="row"
></my-component>
></my-detail-row>
</ng-container>
</my-table>
在周围的组件(包含rows
)中,我有onClickRow(row)
函数切换row.isExpanded
。
在my-component
组件中,我想将row.isLoading
设置为true(通知&#34;父级&#34;它正在加载的行),然后在API调用后将其设置为false完成。
@Input() data: any;
ngOnInit() {
this.task.isLoading = true; // PROBLEM
setTimeout(() => { // simulate API call
this.task.isLoading = false; // no problem
}, 2000);
}
现在我收到此错误:Error: ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked. Previous value: 'undefined'. Current value: 'true'.
我想这是因为更改从my-component
上升到ng-container
,但后来不是my-table-row
?
我有一个解决方法,因为我可以在setTimeout()
的第一个设置周围使用第二个this.task.isLoading
,但是这会产生一些popin效果,我想找到一个更清洁的解决方案可能的。
是否有人有任何建议,这是如何运作的?
答案 0 :(得分:0)
I found a solution that I can live with.
You can inject the "parent" into your component (similar to require
in AngularJS).
For this to work, you need to combine my-table-row
and my-detail-row
into something like my-item-row
. This has the added benefit, that you can put the toggling-logic into the component and don't have to re-implement it on every use.
my-item-row.component.html
:
<div
class="item-row"
(click)="onToggleDetail()"
>
<div class="cell">...</div>
<div *ngIf="isLoading" class="loading"></div>
</div>
<div
*ngIf="isExpanded"
[hidden]="!isInitialized"
class="detail-row"
>
...
</div>
my-item-row.component.ts
:
import { Component } from '@angular/core';
import { Input, ChangeDetectorRef } from '@angular/core';
@Component({...})
export class MyItemRowComponent {
...
isInitialized: boolean = false;
isLoading: boolean = false;
isExpanded: boolean = false;
constructor(private changeDetector: ChangeDetectorRef) { }
onToggleDetail() : void {
this.isExpanded = !this.isExpanded;
}
public startLoading() : void {
this.isLoading = true;
this.isInitialized = false;
this.changeDetector.detectChanges(); // trigger re-evaluate
}
public stopLoading() : void {
this.isLoading = false;
this.isInitialized = true;
this.changeDetector.detectChanges(): // trigger re-evaluate
}
}
Now, you can inject this into my-component
, like this:
my-component.component.ts
:
import { Component } from '@angular/core';
import { Input, Host, Optional } from '@angular/core';
import { MyItemRowComponent } from '...';
@Component({...})
export class MyComponentComponent {
...
// Optional, because there may be a case where we want to use it outside of a row
constructor(@Optional() @Host() private parent: MyItemRowComponent) { }
ngOnInit() { // or ngAfterViewInit, doesn't matter
if (this.parent) {
this.parent.startLoading();
}
setTimeout(() => { // simulate API call
if (this.parent) {
this.parent.stopLoading();
}
}, 2000);
}
}
This is my current solution.
This lead to a different issue with the my-component
being initiated, even when it wasn't expanded yet, see here: