validation - angular2 - validating FormControlName in child component of parent FormGroup

Question

I have an angular component corresponding a form/page that is generating an indeterminate amount of child components, each representing an individual field, and I would like the parent component's FormGroup to validate the fields contained in the child components. Only when I do so, I get an error:

A FormControlName must have a corresponding FormGroup.

Here is the template code for my parent component:

<div class="form-group" [formGroup]="parentGroup">
  <table>
    <tbody>
      <tr *ngFor="let i of array">
        <child [property]="i" [options]="myForm.controls[i.id]"></child>
      </tr>
    </tbody>
  </table>
</div>

The form is defined in the component file here. I'm adding the FormControls according to how many child components we're adding:

private formAttrs: FormGroup;

constructor(private _fb: FormBuilder) { }

ngOnInit() {
  this.myForm = this._fb.group({});
  for (var i = 0; i < this.array.length; i++) {
    this.formAttrs.addControl(this.array[i].id, new FormControl(this.array[i].value, Validators.required));
  }
}

The template code for the child component is this:

<td class="prompt">
  {{i.label}}
</td>
<td class="required" width="1%">
  <span *ngIf="property.required">*</span>
</td>
<td>
  <input type="text " class="form-control" [ngClass]="{error: !options.valid}" formControlName="property.id">
</td>
<td>

While there is nothing defined in the child component class (other than the "property" and the FormControl element passed down for "options"), I would think that the formGroup in the parent component would be able to match with the formControlName in the child component, but instead I get the error:

EXCEPTION: Error in ./ChildComponent class ChildComponent - inline 
template:7:109 caused by: formControlName must be used with a parent 
formGroup directive.  You'll want to add a formGroup directive and pass 
it an existing FormGroup instance (you can create one in your class).

Is there a way I can get around this error? If not, is there another solution to this problem that someone can suggest?

Thanks in advance.

Answer 1

There are a couple of things I came across implementing this in a Plunker.

First, we'll need to pass in our formGroup from the parent to the child so we have a FormGroup to satisfy the templating engine's enforcement of FormControls being a part of a FormGroup:

child.component.ts

@Input() parentGroup: FormGroup;

child.component.html

<td [formGroup]="parentGroup">
<...>
</td>

Then we'll also need to set the [formControl] or evaluate property.id, otherwise it looks for the name "property.id":

<input type="text " class="form-control" [ngClass]="{error: !options.valid}" [formControl]="options"/>

or

<input type="text " class="form-control" [ngClass]="{error: !options.valid}" formControlName="{{property.id}}"/>

Your code was using different variables binding the formGroup and using formAttrs which was a little unclear as to what was going on so I went ahead and collapsed them to one and you can see that in the Plunker: http://plnkr.co/edit/3MRiO9bGNFAkN2HNN7wg?p=preview