ERROR Error: formControlName must be used with a parent formGroup directive.  You'll want to add a formGroup
       directive and pass it an existing FormGroup instance (you can create one in your class).

      Example:

      
    <div [formGroup]="myGroup">
      <input formControlName="firstName">
    </div>

    In your class:

    this.myGroup = new FormGroup({
       firstName: new FormControl()
    });

情况一：没有FormGroup，使用FormControlName

情况二：有FormGroup，没有FormControlName而是使用[(ngModel)]

总而言之，FormGroup和FormControlName必须同时存在