angular5响应式表单动态添加元素

    this.editModel = fb.group({
      params: this.fb.array([
        new FormGroup({
          x: new FormControl(null),
          y: new FormControl(null)
        })
      ]),
    });


  // this.index = 0;
   // this.dynamicArr = [];

  addForm (flag) {
    this.index += 1;
    this.dynamicArr.push({
      id: this.index,
      value: `obj${this.index}`
    });
    (this.editModel.controls[flag] as FormArray).push(new FormGroup({x: new                 FormControl(null), y: new FormControl(null)}));
  }

  minusForm(index, flag) {
    this.dynamicArr.splice(index, 1);
    (this.editModel.get(flag) as FormArray).removeAt(index);
  }

 

      <div class="ui-grid-row">
        <div class="ui-grid-col-2"></div>
        <div class="ui-grid-col-8">
          <label>参数：</label>
          <i class="fa fa-plus-square" aria-hidden="true" style="cursor: pointer;" (click)="addForm('params')"></i>
        </div>
      </div>
      <div formArrayName="params" class="ui-grid-row margin-bottom-1vw" *ngFor="let item of editModel.get('params')['controls']; let i = index;">
        <div class="ui-grid-col-2"></div>
        <div class="ui-grid-col-8" [formGroupName]="i">
          <label></label>
          <p-dropdown [options]="parameterOption" formControlName="x" filter="true" [style]="{'width': '130px'}"></p-dropdown>
          <span>-</span>
          <input type="text" formControlName="y" pInputText [style.width.%]="30"/>
          <i class="fa fa-minus-square" aria-hidden="true" style="cursor: pointer;" (click)="minusForm(i, 'params')"></i>
        </div>
      </div>