ionic-framework/angular/src/directives/control-value-accessors/boolean-value-accessor.ts

import { Directive, ElementRef, HostListener } from '@angular/core';
import { ControlValueAccessor, NG_VALUE_ACCESSOR } from '@angular/forms';

import { setIonicClasses } from './util/set-ionic-classes';

@Directive({
  /* tslint:disable-next-line:directive-selector */
  selector: 'ion-checkbox,ion-toggle',
  providers: [
    {
      provide: NG_VALUE_ACCESSOR,
      useExisting: BooleanValueAccessor,
      multi: true
    }
  ]
})
export class BooleanValueAccessor implements ControlValueAccessor {

  constructor(private element: ElementRef) {
    this.onChange = () => {/**/};
    this.onTouched = () => {/**/};
  }

  onChange: (value: any) => void;
  onTouched: () => void;
  private lastValue: any;

  writeValue(value: any) {
    this.element.nativeElement.checked = this.lastValue = value;
    setIonicClasses(this.element);
  }

  @HostListener('ionChange', ['$event.target.checked'])
  _handleIonChange(value: any) {
    if (value !== this.lastValue) {
      this.lastValue = value;
      this.onChange(value);
    }

    requestAnimationFrame(() => {
      setIonicClasses(this.element);
    });
  }

  @HostListener('ionBlur')
  _handleBlurEvent() {
    this.onTouched();

    requestAnimationFrame(() => {
      setIonicClasses(this.element);
    });
  }

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

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

  setDisabledState(isDisabled: boolean) {
    this.element.nativeElement.disabled = isDisabled;
  }
}