Angular2从指令访问ngModel变量

# 在Angular2中如何从指令访问ngModel变量

typescript
import { Directive, forwardRef } from '@angular/core';
import { NG_VALUE_ACCESSOR, ControlValueAccessor } from '@angular/forms';
@Directive({
  selector: '[appCustomDirective]',
  providers: [
    {
      provide: NG_VALUE_ACCESSOR,
      useExisting: forwardRef(() => CustomDirective),
      multi: true,
    },
  ],
})
export class CustomDirective implements ControlValueAccessor {
  private innerValue: any;
  // 提供一个setter方法，用于在ngModel变量发生变化时更新指令内部的值
  set value(v: any) {
    if (v !== this.innerValue) {
      this.innerValue = v;
      this.onChangeCallback(v);
    }
  }
  // 用于在指令内部值发生变化时通知ngModel的回调函数
  private onChangeCallback: (_: any) => void = () => {};
  // 实现ControlValueAccessor接口的方法
  writeValue(value: any): void {
    if (value !== this.innerValue) {
      this.innerValue = value;
    }
  }
  registerOnChange(fn: any): void {
    this.onChangeCallback = fn;
  }
  registerOnTouched(fn: any): void {}
  setDisabledState?(isDisabled: boolean): void {}
}