Form with Custom Component does not recognize control

Question

I am using a custom component (custom-text) which has the below code

    @Component({
      selector: \'custom-text, [custom-text]\',
      templateUrl: \'./         


        

Answer 1

thinking about your problem really you needn't make a custom form component, just a component that pass as input the form control. Just add an Input

@Input() control
//And in .html
<mat-form-field>
      <input matInput 
            id="controlid" 
            name="controlname" 
            maxlength="8"
            [formControl]="control">
</mat-form-field>

You use the component like

<form #someForm="ngForm">
    <div custom-text [control]="someForm.controls['controlId']"></div>
</form>

Answer 2

I leave in stackblitz the most simple custom form control based in material input.

As you see implements ControlValueAccessor, that's has the functions:

onChange:any; //declare this function to indicate in any time that you change the value
onTouched:any; //declare this function to indicate in any time that your compoment is touched

 writeValue(value: any[]|any): void {
    this.value=value;
  }

  registerOnChange(fn: any): void {
    this.onChange = fn;
  }

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

  setDisabledState(isDisabled: boolean): void {
    this.disabled=isDisabled
  }

And a provider like

   {
      provide: NG_VALUE_ACCESSOR,
      useExisting: forwardRef(() => CustomMat),
      multi: true
    }

If you want to make a validation inside the component, you need add a new provider

   {
      provide: NG_VALIDATORS,
      useExisting: forwardRef(() => CustomMat),
      multi: true,
    }

And create the function validate

validate(control: AbstractControl): ValidationErrors | null{
      //your logic here
      return null;
  }

I used this two more functions:

setValue(value: any){
    this.value=value;
    this.onChange(value);

  }
  focusOut()
  {
    this.onTouched()
  }

To call a change and a touched functions

Updated 01.04.20 well, the problem of this custom material input is that the error can not see reflected in the input, so we are going to make some change

The idea is add a customError matcher

export class CustomFieldErrorMatcher implements ErrorStateMatcher {
  constructor(private customControl: AbstractControl,private errors:any) { }

  isErrorState(control: AbstractControl | null, form: FormGroupDirective | NgForm | null): boolean {
    return this.customControl && this.customControl.touched && this.customControl.invalid;
  }
}

That's our inner input is invalid if the control is invalid. Well, are a dificult that is know what is the this "control". For this, in ngAfterViewInit we inject the NgControl, and this ngControl will be our control, puff

ngAfterViewInit(): void {
    const ngControl: NgControl = this.injector.get(NgControl, null);
    if (ngControl) {
      setTimeout(() => {
        this.control = ngControl.control;
         this.matcher = new CustomFieldErrorMatcher(this.control,null);
      })
    }
  }

At least add this matcher

  <input name="input" matInput [ngModel]="value"
    (ngModelChange)="setValue($event)" 
    [errorStateMatcher]="matcher" >

You can see in this stackblitz