mat-slide-toggle shouldn't change it's state when I click cancel in confirmation window

问题

When I checked the slide toggle it should work as expected. But when I try to uncheck it there is a confirmation window asking if you are sure. When I click cancel in that confirmation window, still the toggle changes to unchecked, which shouldn't happen. It should stay in the same state.

Here is my Html and TS Code

// html
<mat-slide-toggle 
   (change)="change($event)" [checked]="isChecked()" >
     To-pay
   </mat-slide-toggle>

TS code:

// ts
    change(e) {
       if(this.checked) {
           if(confirm("Are you sure")) {
              console.log("toggle")
           }
           else {
              e.stopPropagation();
                console.log("toggle should not change if I click the cancel button")
           }
        }
    }

when the confirmation window comes while trying to uncheck the toggle button and I click the cancel option there, nothing should happen to the toggle. stopPropagation() is also not working.

Edit1 :I tried doing return false in else statement. didn't worked. Even tried to change the e.checked = false. It just changed the event object value but didn't prevent the toggle from slidding

回答1:

Unfortunately you cannot use stopPropagation with mat-slide-toggle, you will need to programmatically set the checked value back to true on the event in your else condition.

else {
    e.source.checked = true;
    console.log("toggle should not change if I click the cancel button")
}

Stackblitz

https://stackblitz.com/edit/angular-79yf7m?embed=1&file=app/slide-toggle-overview-example.ts

回答2:

You can prevent the toggle mechanism by listening for click event and then event.preventDefault() / event.stopImmediatePropagation(). Then open your dialog and according to the user selection you toggle the toggle yourself or not: toggleReference.toggle().

No need to set it back to true.

回答3:

I was using MatDialog as the confirmation window and I noticed the following behavior: when MatDialog is opened, the mat-slide-toggle displays as false / unchecked value, even if the user has not made a decision:

Demo: https://stackblitz.com/edit/angular-79yf7m-4gdxbu?file=app/slide-toggle-overview-example.ts

That's because the change event fires after the mat-slide-toggle value changes.

In order to fix this issue, we have to reset the value to its previous (true) immediately after the change event fires, then let the user decide, and if it confirms the action, we'll update the value accordingly.

The code would be:

change(e) {
  if (this.checked) {
    // at first, reset to the previous value
    // so that the user could not see that the mat-slide-toggle has really changed
    e.source.checked = true;

    const dialogRef = this.dialog.open(ConfirmDialogComponent);
    dialogRef.afterClosed().subscribe(response => {
      if (response) {
       this.checked = !this.checked;
      }
    })
  } else {
    this.checked = !this.checked;
  }
}

Demo: https://stackblitz.com/edit/angular-79yf7m-yzwwc7?file=app%2Fslide-toggle-overview-example.ts

回答4:

I think the matter is the (change)="eventHandler()" will fire AFTER the value change, while the (ngModelChange)="eventHandler()" will fire BEFORE the value change

来源：https://stackoverflow.com/questions/54005182/mat-slide-toggle-shouldnt-change-its-state-when-i-click-cancel-in-confirmation