NG_VALUE_ACCESSOR

用于为表单控件提供 ControlValueAccessor

interface ControlValueAccessor {
  writeValue(obj: any): void
  registerOnChange(fn: any): void
  registerOnTouched(fn: any): void
  setDisabledState(isDisabled: boolean)?: void
}

双向绑定 示例组件：

import {
  ChangeDetectionStrategy,
  ChangeDetectorRef,
  Component,
  forwardRef,
} from '@angular/core';
import { NG_VALUE_ACCESSOR, ControlValueAccessor } from '@angular/forms';
 
@Component({
  selector: 'my-input',
  styleUrls: ['./my.input.component.scss'],
  changeDetection: ChangeDetectionStrategy.OnPush,
  providers: [
    {
      provide: NG_VALUE_ACCESSOR,
      useExisting: forwardRef(() => MyInputComponent),
      multi: true,
    },
  ],
  template: `
    <input type="text" #inputElement 
        [(ngModel)]="value"  
        (ngModelChange)="modelChange($event)"/>
    <button (click)="clickMe()">change</button>
  `
})
export class MyInputComponent implements ControlValueAccessor {
  
  private onTouch = () => {};
  private onChange = (newValue: any) => {};
 
  value = '';
  index = 0; // for test manual change value
 
  constructor(
    private cdr: ChangeDetectorRef
  ) { }


  clickMe() {
    const v = 'index : ' + (++this.index);
    this.value = v;
    this.onChange(v);
  }

    
  modelChange(newValue: string) {
    this.onChange(newValue);
  }
 
  // ControlValueAccessor - 
  // 至少需要实现 writeValue, registerOnChange,registerOnTouched
  writeValue(v: any) {
    if (v !== this.value) {
      this.value = v;
    }
    // on push
    this.cdr.markForCheck();
  }
 
  registerOnChange(fn: any) {
    this.onChange = fn;
  }
 
  registerOnTouched(fn: any) {
    this.onTouch = fn;
  }
}

registerOnTouched 的参数 fn：

 registerOnChange 的参数 fn ：