Feature: expose the ngDefaultControl

[gogoout]

Currently all the form controls have implemented the ControlValueAccessor. While if the users wants to wrap the form controls themselves, it will be quite redundant. They have to implement the ControlValueAccessor all over again.

In here, the way is much more easier thanks to the ngDefaultControl which Angular exposed.

@Component({
  selector: 'my-wrapper',
  template: '<input ngDefaultControl>',
  providers: [
    {
      provide: NG_VALUE_ACCESSOR,
      useExisting: forwardRef(() => NumberInputComponent),
      multi: true,
    },
  ],
})
export class MyWrapper implements ControlValueAccessor {
  @ViewChild(DefaultValueAccessor) private valueAccessor: DefaultValueAccessor;

  writeValue(obj: any) {
    this.valueAccessor.writeValue(obj);
  }

  registerOnChange(fn: any) {
    this.valueAccessor.registerOnChange(fn);
  }

  registerOnTouched(fn: any) {
    this.valueAccessor.registerOnTouched(fn);
  }

  setDisabledState(isDisabled: boolean) {
    this.valueAccessor.setDisabledState(isDisabled);
  }
}

The way doesn't work in the nativescript-angular because the ngDefaultControl is not exposed in here.
By simply put the ngDefaultControl selector in all the value-accessor. We can implement the same feature.

[gms1]

If I understand that correctly, you want to use the 'ngDefaultControl' directive for NOT binding an element to this 'DefaultValueAccessor':
https://github.com/angular/angular/blob/master/packages/forms/src/directives/default_value_accessor.ts
but you still like to get a reference to this 'DefaultValueAccessor' using "@ViewChild (DefaultValueAccessor)"?

[gogoout]

No, I believe that's not what I want. I'll try to explain in detail.
The thing is I want to wrap a TextView(or Switch/ListPicker/... etc) into a custom component kind like this:

@Component({
    selector: 'ag-float-input',
    moduleId: module.id,
    template: '<TextField  ngDefaultControl></TextField>'
    providers: [
        {
            provide: NG_VALUE_ACCESSOR,
            useExisting: forwardRef(() => FloatInputComponent),
            multi: true,
        },
    ],
})
export class FloatInputComponent implements ControlValueAccessor, AfterViewInit {
   @ViewChild(TextValueAccessor) private valueAccessor: TextValueAccessor;

   public writeValue(value: string): void {
        this.valueAccessor.writeValue(value);
    }

  ...
}

The problem here is that I can't get the TextValueAccessor directive here because the selector of the direcitve is

from https://github.com/NativeScript/nativescript-angular/blob/master/nativescript-angular/forms/value-accessors/text-value-accessor.ts

"TextField[ngModel],TextField[formControlName],TextField[formControl]," +
        "textField[ngModel],textField[formControlName],textField[formControl]," +
        "textfield[ngModel],textfield[formControlName],textfield[formControl]," +
        "text-field[ngModel],text-field[formControlName],text-field[formControl]," +
         ....

What I want to do is adding a selector to the Nativescript selector so that I can get a reference to the TextValueAccessor

So the selector will turn into something like this:

"TextField[ngModel],TextField[formControlName],TextField[formControl], TextField[ngDefaultControl]," +
        "textField[ngModel],textField[formControlName],textField[formControl],textField[ngDefaultControl]," +
        "textfield[ngModel],textfield[formControlName],textfield[formControl],textfield[ngDefaultControl]," +
        "text-field[ngModel],text-field[formControlName],text-field[formControl],text-field[ngDefaultControl]," +

Well, to be honest, I'm still new to the Nativescript and Angular so I'm not sure if this is going to work. But the idea is to expose a way to get the Nativescripts' TextValueAccessor(and also other value accessors) so that we can easily wrap the native form component into a custom one.

[gms1]

ok, but the actual name of the attribute selector is almost completely irrelevant for this use case.

For example, if the TextValueAccessor would have the '[nsDefaultTextControl]' attribute declared and you would use that attribute for a TextField element, you should be able to resolve the TextValueAccessor instance by using @ViewChild(TextValueAccessor).

On the other hand, if the TextValueAccessor AND the DefaultValueAccessor would have the same '[ngDefaultControl]' attribute declared, angular should find two different value accessors for the same css selector and should throw an error

see angular/angular#3011

[gogoout]

Thanks, that make sense.