Add 'compareWith' option to mat-radio-group just like mat-select

[CurtisDS]

Bug, feature request, or proposal:

Feature request: There is an issue with the mat-radio-group. If you use an object as the value for the form control the corresponding radio button is not checked. It only uses reference based comparison for checking which button should be highlighted.

I would like the ability to specify a comparison method to use while the mat-radio-group is deciding which item is selected. Just like how you can already specify a 'compareWith' method for a mat-select control.

What is the expected behavior?

If you use basic values it works as expected. Example here. In this case the value is set to 1.1 and the 'one,one' button is selected.

What is the current behavior?

However when you use an array, it does not work. Example here. In this case the value is set to [1,1] and none of the buttons are selected. Even though the form control's value is clearly shown to be [1,1].

What is the use-case or motivation for changing an existing behavior?

I am currently trying to dynamically generate a form based on some data given back from an API. The api gives me choices and a selected value to show by default.

{ tag: 'radio button', value: '[0,1]', choices: [ { tag: 'option 1', value: [0,0] }, { tag: 'option 2', value: [0,1] } ] }

In the spec for mat-radio-group and mat-radio-button the value is of type any. So it should support any type of value I want to use.

The current mat-select control already possesses this feature and I would like to see it paralleled in the radio button control. Here is an example of the select control with the 'compareWith' attribute. As you can see it selects the "one,one" value by default.

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Angular: 5.2.6
@angular/material: 5.2.3
typescript: 2.4.2

[julianobrasil]

This is not material fault. That's how javascript works: you're comparing different objects. If you change your code to the following, it'll work:

seasons = [
  { value : [1,0], tag : 'one,zero' },
  { value : [2,0], tag : 'two,zero' },
  { value : [3,0], tag : 'three,zero' },
  { value : [1,1], tag : 'one,one' },
  { value : [2,1], tag : 'two,one' },
  { value : [3,1], tag : 'three,one' }
];

selectedValue  = this.seasons[3].value; // same array, not a 'similar' one
favoriteSeason: FormControl = new FormControl(this.selectedValue);

you were doing selectedValue=[1,1]; in your example code. To javascript (and almost every programming language), [1,1] == [1,1] is false: they are similar arrays, but not equal arrays (the array comparison actually compares references, not values).

[CurtisDS]

you were doing selectedValue=[1,1]; in your example code. To javascript (and almost every programming language), [1,1] == [1,1] is false: they are similar arrays, but not equal arrays (the array comparison actually compares references, not values).

Yes I understand that is how it works. I brought it up in the end bit of my post there. I consider it a bug to not use a value based comparison on objects for setting the selected item but I would be willing to change my wording and make it a feature request instead if that is more appropriate. Asking for the ability to provide my own comparison method to the radio group. So that I can have a values based comparison, instead of a reference based one.

[julianobrasil]

Well, other components have something similar to *ngFor's trackBy. I've never thought of mat-radio-group as a component similar to mat-select, but now I'm reconsidering my position. In the sense of this use case IMO, it would be nice to have such a feature, but someone from the material team will surely give you a more accurate info about it.

[CurtisDS]

Yes, I didn't realize select already had this feature. Thank you for that, it makes it a lot easier to communicate what I would like. I have edited my post.

[CurtisDS]

I found a semi work around. By using the 'checked' attribute of the radio button and setting it equal to the result of the same compare function written for the select. Here is that example. However there is still a hiccup where if you reset the value of the form control, while the form control is already set to the default value, it will uncheck all the radio buttons. So ill have to add more code to block the reset function from resetting the value if its already equal to the default value.

I still think implementing the same compareWith function is the better solution, especially for consistency. But I guess this is an ok workaround for now.

[keatkeat87]

sometime, we change the select to radio group is just because of user experience.
user want to see all selection all the time.
so i think compare With is a necessary feature.

[cvaliere]

in case someone wants a directive to do that:

import { AfterContentInit, ContentChildren, Directive, EventEmitter, Input, OnChanges, Output, QueryList, SimpleChanges } from '@angular/core';
import { MatRadioButton } from '@angular/material';
import { AutoUnsubscribe } from '@bemyeye/auto-unsubscribe';
import { BehaviorSubject } from 'rxjs';
import { takeUntil } from 'rxjs/operators';

/**
 * Add 'compareWith' to mat-radio-group just like mat-select, because angular team didn't implement it
 * see https://github.com/angular/components/issues/10495
 */
@Directive({
  selector: 'mat-radio-group[bmeCompareWith]',
})
export class RadioGroupCompareWithDirective<T> extends AutoUnsubscribe implements AfterContentInit, OnChanges {

  @Input() bmeCompareWith: (o1: T, o2: T) => boolean;
  @Input() ngModel: T;

  @Output() ngModelChange = new EventEmitter<T>();

  @ContentChildren(MatRadioButton, { descendants: true }) radioButtons: QueryList<MatRadioButton>; // List of descendant RadioButtons

  ngOnChangesModel = new BehaviorSubject<T>(null);

  ngAfterContentInit() { // Use ngAfterContentInit to make sure that radioButtons is initialized
    this.ngOnChangesModel.pipe(
      takeUntil(this.componentDestroyed)
    ).subscribe(() => {
      const foundRadioButton = this.radioButtons.toArray().find(radioButton => { // Find a radio button whose value compares to ngModel
        return this.bmeCompareWith(radioButton.value, this.ngModel);
      });
      if (foundRadioButton) { // If radio button is found
        if (this.ngModel !== foundRadioButton.value) { // But its value is not already the ngModel
          this.ngModelChange.emit(foundRadioButton.value); // Then emit the new value
        }
      }
    });
  }

  ngOnChanges(changes: SimpleChanges): void {
    if (changes.ngModel) {
      this.ngOnChangesModel.next(changes.ngModel.currentValue);
    }
  }

}

[cvaliere]

with the class AutoUnsubscribe, which is useful too :)

import { OnDestroy } from '@angular/core';
import { Subject } from 'rxjs';

/**
 * Extend this class in order to autounsubscribe all subscriptions of a component onDestroy
 * Usage: replace XXX.subscribe() with XXX.takeUntil(this.componentDestroyed).subscribe()
 * See https://stackoverflow.com/questions/38008334/angular-rxjs-when-should-i-unsubscribe-from-subscription
 */
export class AutoUnsubscribe implements OnDestroy {
  protected componentDestroyed = new Subject<void>();

  constructor() {

    // wrap the ngOnDestroy to be an Observable. and set free from calling super() on ngOnDestroy.
    const _$ = this.ngOnDestroy.bind(this);
    this.ngOnDestroy = () => {
      this.componentDestroyed.next();
      this.componentDestroyed.complete();
      _$();
    };
  }

  ngOnDestroy() {
    // placeholder of ngOnDestroy. no need to do super() call of extended class.
  }
}

[Diegovictorbr]

Any updates on this? It is really necessary in edition forms when you want to set an object as a value for a radio group.