如何获取角形数组中已更改项的索引

我将项添加到表单数组中,如下所示：

createFormWithModel() {
  this.orderForm = this.fb.group({
    orderNumber: [this.order.ProductBookingOrder],orderDate: [this.order.PurchaSEOrderIssuedDate],lineDetailsArray: this.fb.array([])
  })

  const arrayControl = <FormArray>this.orderForm.controls['lineDetailsArray'];
  this.order.ProductBookingDetails.forEach(item => {
    let newGroup = this.fb.group({
      ProductName: [item.ProductName],Quantity: [item.ProductQuantity.Quantity],UOM: [item.ProductQuantity.UOM],RequestedShipDate: [item.RequestedShipDate]
    })
  })
}

orderForm显然是我的反应形式FormGroup.订单是我从API获取的对象,我想更新其值,包括行详细信息.我想我应该在每个newGroup上使用’valueChanges.subscribe’,但我不确定如何获取已更改的项的索引.有什么想法吗？

newGroup.valueChanges.subscribe('i want value and index some how' => {
this.order.ProductbookingDetails[index].ProductName = value.ProductName;
    });

这是这部分的HTML：

<tbody formArrayName="lineDetailsArray">
        <tr [formGroupName]="i" *ngFor="let line of orderForm.controls['lineDetailsArray'].controls; index as i">
          <td><input class="form-control" type="text" placeholder="Product Name" formControlName="ProductName" required/></td>
          <td><input class="form-control" type="number" step=".01" (focus)="$event.target.select()" placeholder="Quantity" formControlName="Quantity"/></td>
          <td><input class="form-control" readonly formControlName="UOM"></td>
          <td><date-picker formControlName="RequestedShipDate" format="L" [showClearButton]="false"></date-picker></td>
          <td><button type="button" (click)="deleteLineDetail(i)">Remove</button></td>
        </tr>
      </tbody>