如何在自定义的组件(form 控件)中找到FormControl

懒的翻译了，翻也翻不通顺，直接上原文（其实我就是个搬运工......）

As we can't get NgControl instance directly from DI system since we'll get a circular dependency error. The following diagram shows why it happens if we inject NgControl in our custom value accessor:

Now it should be clear that we have NgControl -> FormControlName -> ValueAccessor -> CustomValueAccessor -> NgControl circular dependency

To work around it you can leverageInjector to achieve that:

component.ts

import { NgControl } from '@angular/forms';
export class PasswordComponent implements ControlValueAccessor {
  ...
  ngControl: NgControl;

  constructor(private inj: Injector) {
    ...
  }

  ngOnInit() {
    this.ngControl = this.inj.get(NgControl)
  }

Plunker Example