更改后角度8值将不会在视图上更新

Question

I have a small component in Angular with a method that (for now) sets a timeout and changes the value of a variable.

import { Component, ChangeDetectionStrategy } from '@angular/core';

@Component({
  selector: 'my-component',
  templateUrl: './my-view.html',
  styleUrls: ['./my-view.scss'],
  changeDetection: ChangeDetectionStrategy.Default
})
export class MyComponent {

  status: boolean = false;

  changeStatus(): void {

    setTimeout(() => {
      this.status = true;
    }, 1500);
  }
}

And the HTML

<div>
  <form #myForm="ngForm">
    <input name="code" type="text" class="form-control" [(ngModel)]="code" #codeInput="ngModel" required placeholder="Enter your code" />
  </form>
</div>

<div class="row">
  <div class="col-md-5" (click)="changeStatus()">
    <mat-icon aria-label="clear-all" *ngIf="!status">&#xe042;</mat-icon>
    <a>Change status</a>
  </div>
  <div class="col-md-7">
    <button type="button" class="btn-flat app-btn-flat">Cancel</button>
    <button type="button" class="btn app-btn" [disabled]="myForm.invalid || myForm.pristine">Save</button>
  </div>
</div>

If I log the value of 'status' in the component. I get the new value of 'true' but it won't change on the view unless I focus the cursor on the input and then click anywhere outside it.

Why is that happening? how can I solve it?

Answer 1

You're doing it outside of the normal change detection cycle. This will work:

export class MyComponent {

  status: boolean = false;

  constructor(private _cdr: ChangeDetectorRef) { }

  changeStatus(): void {

  setTimeout(() => {
    this.status = true;
    this._cdr.detectChanges()
  }, 1500);
 }
}

EDIT : It's updating on your next interaction with the UI because angular is running it's change detection at that point in time and it catches the change in your component and updates the UI. If you're doing things asynchronously (unless you're using angular APIs, like HttpService), then you've got to tell the ChangeDetector that there are changes manually.

Answer 2

Why is that happening?

You set changeDetection to OnPush in one of the ancestor component. That property cannot be overridden. Ref: https://angular.io/api/core/ChangeDetectionStrategy

how can I solve it?

Unset changeDetection in the ancestor component, or manually detect changes like Adam's answer.

constructor(private _cdr: ChangeDetectorRef) {}

changeStatus(): void {
  setTimeout(() => {
    this.status = true;
    this._cdr.detectChanges()
  }, 1500);
}