解决Angular2动态表单丢失焦点问题

<div *ngFor="let value of field.values; let i=index; trackBy:trackByFn">
    <input type="text" [(ngModel)]="field.values[i]"  /><br/>
</div>
<div>
    <button (click)="addValue(field)">Click</button>
</div>

trackByFn(index: any, item: any) {
   return index;
}