错误错误：找不到路径控制

我是Angular的新手并试图扩展示例代码：Angular 4 Form FormArray Add a Button to add or delete a form input row

如果在下拉列表中选择了某个选项，则该选项的新选项应该是可表达的 . 我没有遇到任何问题，但为那些'lower-tier-options'实现formControlName标签会给我一个错误：

ContentComponent.html：56错误错误：找不到带路径的控件：'inhalt - > 0 - > optionsKey'（...）.html中的确切行是:(输入formControlName =“optionsKey”）

我在其他线程（Angular 2 Form "Cannot find control with path"）或（Angular 2 Reactive Forms: Cannot find control with path）或（Error: Cannot find control with path: 'x ' angular 2）中查找了这些错误，但是它们的问题是基于在没有FormBuilder的情况下创建ReactiveForm-Components . 我使用Formbuilder创建了所有的ReactiveForm-Components，您将在我的代码中看到它 .

我可能错过了什么或者做错了吗？

content.html

<h3 class="page-header">Formular-Abschnitt hinzufügen</h3>
<button type="button" (click)="addNewFormControl()" class="btn btn-primary">Neues Formularelement</button><br>
<form [formGroup]="formContent">
  <div>
    <label>Bezeichnung des Abschnittes</label>
    <input formControlName="absatz">
  </div>
  <div formArrayName="inhalt">

    <!--
    In the template we are iterating this formarray,
        and that is just the path to the formarray, which is:

        invoiceForm.controls.itemRows.controls

        'invoiceForm' being the complete form object, 'controls' being the content of the form object,
        'itemRows' being the (form)array in the form, 'controls' being the content of the formarray.

    -->

    <div *ngFor="let itemrow of formContent.controls.inhalt.controls; let i=index" [formGroupName]="i">
      <h4>Formular-Element #{{ i + 1 }}</h4>
      <div class="form-group">
        <label>Element-Name</label>
        <input formControlName="label" class="form-control">
      </div>
      <div class="form-group">
        <label>Element-Key</label>
        <input formControlName="key" class="form-control">
      </div>
      <div class="form-group">
        <label>Element-zwingend notwendig?</label>
        <input type="checkbox" formControlName="required" class="form-control">
      </div>
      <div class="form-group">
        <label>Element-Position</label>
        <input formControlName="order" class="form-control">
      </div>
      <div class="form-group">
        <label>Element-Art</label>
        <select formControlName="controlType" class="form-control">
          <option>InputField</option>
          <option>Checkbox</option>
          <option>Radiobutton</option>
          <option>Dropdown</option>
          <option>Beschreibungstext</option>
        </select>
        <div [ngSwitch]="formContent.value.inhalt[i].controlType">
          <div *ngSwitchCase="'Checkbox'">
            <h3>Optionen definieren:</h3>
            <button (click)="addFormControlOptions()">Neue Option hinzufügen</button>
            <div *ngFor="let test of itemrow.controls.options.controls; let x = index" >
              {{test.controls.optionsKey.value}}
              <div>
                <label >Key: </label>
                <input formControlName="optionsKey" >
              </div>
              <div>
                <label>Value: </label>
                <input>
              </div>
              <button (click)="deleteFormControlOptions(x)">Option entfernen</button>
            </div>



          </div>
          <div *ngSwitchCase="''">
            <p>lololololo</p>
          </div>
          <div *ngSwitchDefault="">
            <p>DEFAULT</p>
          </div>
        </div>


      </div>
      <button *ngIf="formContent.controls.inhalt.controls.length > 1" (click)="deleteFormControl(i)"
              class="btn btn-danger">Delete Button
      </button>
    </div>
  </div>

</form>
<!--<pre>{{formContent.value | json}}</pre>-->
<button type="submit" (click)="saveData()">Formular-Abschnitt speichern</button>

content.ts

import { Component, OnInit } from '@angular/core';
import {Form, FormArray, FormBuilder, FormGroup} from '@angular/forms';
import {isBoolean, isNumber} from 'util';

@Component({
  selector: 'app-content',
  templateUrl: './content.component.html',
  styleUrls: ['./content.component.css']
})
export class ContentComponent implements OnInit {


  public formContent: FormGroup;
  absatz;

  constructor(private _fb: FormBuilder) { }

  ngOnInit() {
    this.formContent = this._fb.group({
      absatz: '',
      inhalt: this._fb.array([this.initFormElements()])
    });
  }
  initFormElements() {
    return this._fb.group({
      label: '',
      key: '',
      order: isNumber(),
      controlType: '',
      required: isBoolean(),
      options: this._fb.array([this.initFormElementOptions()])
    });
  }
  initFormElementOptions() {
    return this._fb.group({
      optionsKey: '',
      optionsValue: ''}
    );
  }
  addNewFormControl() {
    const control = <FormArray>this.formContent.controls['inhalt'];
    control.push(this.initFormElements());
  }
  deleteFormControl(index: number) {
    const control = <FormArray>this.formContent.controls['inhalt'];
    control.removeAt(index);
  }

  saveData() {

    return this.formContent.value;
  }
   addFormControlOptions() {
   // const control = <FormArray>this.formContent.controls['inhalt'].controls[0].options;
   // control.push(this.initFormElementOptions());
   }
   deleteFormControlOptions(index: number) {
     const control = <FormArray>this.formContent.controls['inhalt'].value[0].options;
     control.removeAt(index);
   }
}

Plunker：https://embed.plnkr.co/LIcp9vpGDCAWH9qZacQT/

提前致谢！

Update: 我需要将一个formArrayName = "options"添加到我的SwitchCase，并将formGroupName = "x"（我使用ngFor的索引x）添加到ngFor-Div .