Issue encountered: "ERROR TypeError: Upon attempting to patchValue in ngOnInit(), the property 'form' is undefined."

Can someone help me figure out how to use the patchValue method in the ngOnInit() function? I'm trying to populate a HTML select dropdown with a value from a link, but it's not working as expected.

Note: onTest() works perfectly when called separately.

@ViewChild('FomrElm', {static: false}) RentForm: NgForm;

ngOnInit() {
  if (this.route.snapshot.params['brand'] != null) {
    console.log('::' + this.route.snapshot.params['brand']);
    this.RentForm.form.patchValue({
      Brand: 'Peugeot'
    });
    this.brand_V = this.route.snapshot.params['brand'];
    this.model_V = this.route.snapshot.params['model'];
  } 

  onTest(){
    this.RentForm.form.patchValue({
      Brand: 'Peugeot'
    });
  }
}
angulartypescriptangular-reactive-forms

Answer №1

The form in the parent component's ngOnInit has not been initialized yet. To access the initialized form of the ViewChild, you can implement AfterViewInit.

Check out the stackblitz below for more details:

export class AppComponent implements OnInit, AfterViewInit  {
  
  @ViewChild(UserFormComponent)
  public userForm: UserFormComponent;

  ngOnInit() {
    
  }

  ngAfterViewInit() {
    // The form in ViewChild will now be accessible without being null.
    console.log(this.userForm);
  }

}

Take a look at the console in the stackblitz link below to observe the difference.

https://stackblitz.com/edit/angular-shwrtx

https://angular.io/api/core/AfterViewInit

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