Angular: composite ControlValueAccessor to implement nested form

Question

Composition of ControlValueAccessor to implement nested form is introduced in an Angular Connect 2017 presentation.

https://docs.google.com/presentation/d/e/2PACX-1vTS20UdnMGqA3ecrv7ww_7CDKQM8VgdH2tbHl94aXgEsYQ2cyjq62ydU3e3ZF_BaQ64kMyQa0INe2oI/pub?slide=id.g293d7d2b9d_1_1532

In this presentation, the speaker showed a way to implement custom form control which have multiple value (not only single string value but has two string field, like street and city). I want to implement it but I'm stuck. Sample app is here, does anybody know what should I correct?

https://stackblitz.com/edit/angular-h2ehwx

parent component

@Component({
  selector: 'my-app',
  template: `
    <h1>Form</h1>
    <form [formGroup]="form" (ngSubmit)="onSubmit(form.value)" novalidate>
      <label>name</label>
      <input formControlName="name">
      <app-address-form formControlName="address"></app-address-form>
      <button>submit</button>
    </form>
  `,
})
export class AppComponent  {
  @Input() name: string;
  submitData = '';
  form: FormGroup;

  constructor(private fb: FormBuilder) {
    this.form = fb.group({
      name: 'foo bar',
      address: fb.group({
        city: 'baz',
        town: 'qux',
      })
    });
  }

  onSubmit(v: any) {
    console.log(v);
  }
}

nested form component

@Component({
  selector: 'app-address-form',
  template: `
    <div [formGroup]="form">
      <label>city</label>
      <input formControlName="city" (blur)="onTouched()">
      <label>town</label>
      <input formControlName="town" (blur)="onTouched()">
    </div>
  `,
  providers: [
    {
      provide: NG_VALUE_ACCESSOR,
      multi: true,
      useExisting: forwardRef(() => AddressFormComponent)
    }
  ]
})
export class AddressFormComponent implements ControlValueAccessor {
  form: FormGroup;

  onTouched: () => void = () => {};

  writeValue(v: any) {
    this.form.setValue(v, { emitEvent: false });
  }

  registerOnChange(fn: (v: any) => void) {
    this.form.valueChanges.subscribe(fn);
  }

  setDisabledState(disabled: boolean) {
    disabled ? this.form.disable() : this.form.enable();
  }

  registerOnTouched(fn: () => void) {
    this.onTouched = fn;
  }
}

and error message I got

ERROR TypeError: Cannot read property 'setValue' of undefined
at AddressFormComponent.writeValue (address-form.component.ts:32)
at setUpControl (shared.js:47)
at FormGroupDirective.addControl (form_group_directive.js:125)
at FormControlName._setUpControl (form_control_name.js:201)
at FormControlName.ngOnChanges (form_control_name.js:114)
at checkAndUpdateDirectiveInline (provider.js:249)
at checkAndUpdateNodeInline (view.js:472)
at checkAndUpdateNode (view.js:415)
at debugCheckAndUpdateNode (services.js:504)
at debugCheckDirectivesFn (services.js:445)

I think FormGroup instance should be injected to nested form component somehow...

Answer 1

Couple issues, on your AppComponent change your FormBuilder to:

this.form = fb.group({
  name: 'foo bar',
  address: fb.control({ //Not using FormGroup
    city: 'baz',
    town: 'qux',
  })
});

On your AddressFormComponent you need to initialize your FormGroup like so:

form: FormGroup = new FormGroup({
    city: new FormControl,
    town: new FormControl
});

Here's the fork of your sample: https://stackblitz.com/edit/angular-np38bi