compareWith for RadioControlValueAccessor

[sclausen]

🚀 feature request

Relevant Package

This feature request is for @angular/forms

Description

I want to bind objects to radio button values and need an own function for comparing the ngModel with the value.

Describe the solution you'd like

I suggest the RadioControlValueAccessor should have compareWith like the SelectControlValueAccessor.

Describe alternatives you've considered

[kara]

@sclausen can you add some more detail to this? suggested use, etc

[sclausen]

@kara If I provide an object as my [(ngModel)] and want to have the radio button's [value] to be an object too, the radio button directive never marks the radio as checked, since it compares by strict equality.

If this lines could be copied to the radio_control_value_accessor.ts and writeValue could be changed to the following, it would be easy to implement a custom function to check the identity.

  writeValue(value: any): void {
    this._state = this._compareWith(this.value, value);
    this._renderer.setProperty(this._elementRef.nativeElement, 'checked', this._state);
  }

I would've provided a PR, but don't know how to write a test case for this.

[adam-marshall]

I need this too. I am using [compareWith] for select controls, but there is no equivalent way of getting this to work with radio buttons.

The justification is the same as the following issues, but for radio buttons instead of select:
#13268 (comment)
#13295
#12742
https://stackoverflow.com/questions/40325480/angular2-ngmodel-ngvalue-select-option-object-equality-across-different-instan

Therefore it would probably be intuitive for radio_control_value_accessor.ts to use the same pattern?

[adam-marshall]

There is a related issue on material which this would resolve too: angular/components#10495

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