Angular 4 フォーム FormArray フォーム入力行を追加・削除するボタンを追加する。

    <h3 class="page-header">Add Invoice</h3>
    <form [formGroup]="invoiceForm">
      <div formArrayName="itemRows">
        <div *ngFor="let itemrow of itemRows.controls; let i=index" [formGroupName]="i">
          <h4>Invoice Row #{{ i + 1 }}</h4>
          <div class="form-group">
            <label>Item Name</label>
            <input formControlName="itemname" class="form-control">
          </div>
          <div class="form-group">
            <label>Quantity</label>
            <input formControlName="itemqty" class="form-control">
          </div>
          <div class="form-group">
             <label>Unit Cost</label>
             <input formControlName="itemrate" class="form-control">
          </div>
          <div class="form-group">
            <label>Tax</label>
            <input formControlName="itemtax" class="form-control">
          </div>
          <div class="form-group">
            <label>Amount</label>
            <input formControlName="amount" class="form-control">
          </div>
          <button *ngIf="i > 1" (click)="deleteRow(i)" class="btn btn-danger">Delete Button</button>
        </div>
      </div>
      <button type="button" (click)="addNewRow()" class="btn btn-primary">Add new Row</button>
    </form>
    <p>{{invoiceForm.value | json}}</p>

import { Component, OnInit } from '@angular/core';
import { FormBuilder, FormControl, FormArray, FormGroup } from '@angular/forms';

@Component({
  selector: 'app-add-invoice',
  templateUrl: './add-invoice.component.html',
  styleUrls: ['./add-invoice.component.css']
})

export class AddInvoiceComponent implements OnInit {
  invoiceForm: FormGroup;

  constructor(
    private _fb: FormBuilder
  ) {
    this.createForm();
  }

  createForm(){
    this.invoiceForm = this._fb.group({
      itemRows: this._fb.array([])
    });
    this.invoiceForm.setControl('itemRows', this._fb.array([]));
  }

  get itemRows(): FormArray {
    return this.invoiceForm.get('itemRows') as FormArray;
  }

  addNewRow(){
    this.itemRows.push(this._fb.group(itemrow));
  }

  ngOnInit(){

  }
}