Angular 6：从选择下拉事件触发的ExpressionChangedAfterItHasBeenCheckedError

Question

What code changes can remedy the Error described below ?

Use-case

A drop-down input UI is protected from unintended selected value change via a modal. However, the event (click, focus or other), wired to the drop-down causes the ExpressionChangedAfterItHasBeenCheckedError, observed in Chrome console in dev mode.

Observed result

When drop-down is clicked, an ExpressionChangedAfterItHasBeenCheckedError is thrown (see console)

Expected result

When drop-down is clicked, a Modal opens without error

Demo

A link to demo in stackblitz

Notes

• As described in "Everything you need to know about ExpressionChangedAfterItHasBeenCheckedError" here , I attempt to trigger change detection (see comments inside app.component.ts:48-49, marked as STEP-1 and STEP-2), but unsuccessfully (probably triggered not in the right place?)
• The modal in the demo is not fully implemented for [OK] and [CANCEL] as it doesn't affect the Error
• The code is simplified version of a larger app

Answer 1

What code changes can remedy the Error described below ?

The code like this should help you:

<select 
  [(ngModel)]="building.venueId"
  #ngModel="ngModel"
  ^^^^^^^^^^^^^^^^^^
  get hold of NgModel instance
  ...
  (click)="ngModel.control.markAsTouched(); confirmChangeItem(building.venueId)">
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
           and prepare FormControl to the changes

Forked Stackblitz

Update

I forgot to say that you can remove cdRef.detectChanges and microtask in this case so i'm glad to know you guessed it yourself