Display mat-form-field error message before control is touched

Question

This question has a Stackblitz; stackblitz.com/edit/yz1dhz.

How can mat-form-field validation error messages be rendered when a component loads and before the user has touched the control?

class AppComponent implements OnInit {
  form: FormGroup;

  constructor(private readonly fb: FormBuilder) {
    // Create a form in an invalid state.
    this.form = this.fb.group({
      a: this.fb.control(null, [Validators.required])
    });
  }

  ngOnInit() {
    // This does do what I had hoped.
    this.form.updateValueAndValidity();
  }
}

That code creates a form which is immediately invalid. I expected <mat-error> to show:

<form [formGroup]="form">
    <mat-form-field>
        <mat-select formControlName="a">
            <mat-option>Foo</mat-option>
            <mat-option>Bar</mat-option>
            <mat-option>Baz</mat-option>
        </mat-select>
    <mat-hint>I am a hint.</mat-hint>
    <mat-error>{{ form.controls['a'].errors | json }}</mat-error>
    </mat-form-field>
</form>

But instead the <mat-hint> is displayed.

Answer 1

You can force it that way

this.form.get('a').markAsTouched();

or you can mark all controls as touched

this.form.markAllAsTouched();

you can change the status of a form control using markAsTouched, markAllAsTouched, markAsUntouched, markAsDirty, markAsPristine, markAsPending...