问如何在angularjs webapi中使用ng-change来聚焦表格中的文本框？

EN

$scope.txtqty = function (item) {
    var id = item.Id;
    $http.put("/api/Products/txtqty/" + id, item).then(function (response) {
        $scope.gridproducts = response.data;
    })
}

    <table>
    <tbody>
        <tr ng-repeat="item in gridproducts">
            <td ng-click="griddelete(item.Id)"><a class="delete"><i class="fa fa-times-circle-o"></i></a></td>
            <td class="name">{{item.ProductName}}</td>
            <td>{{item.ProductRate}}</td>
            <td><input class="form-control qty" type="text" style="width:50px" ng-change="txtqty(item)" ng-model="item.ProductQty" value="{{item.ProductQty}}"></td>
            <td>{{item.TotalAmount}}</td>
        </tr>
        <tr></tr>
    <tfoot>
        <tr>
            <th colspan="2"></th>
            <th colspan="2"><b>Total</b></th>
            <th><b>{{gridproducts[0].TotalBill}}</b></th>
            </tr><tr>
            <th colspan="2"><b></b></th>
            <th colspan="2"><b>Total Items</b></th>
            <th><b>25</b></th>
            </tr>
        </tfoot>
</table>

 [System.Web.Http.Route("api/Products/txtqty/{id}")]
        [ResponseType(typeof(void))]
        public IHttpActionResult PuttxtQTY(int id, Product Pro)
        {
            var q = gridlist.Where(x => x.Id == id).FirstOrDefault();
            if (q != null)
            {
                q.ProductQty = Pro.ProductQty;
                q.TotalAmount = q.ProductQty * q.ProductRate;
                q.TotalBill = gridlist.Sum(x => x.TotalAmount);
                foreach (var item in gridlist)
                {
                    item.TotalBill = q.TotalBill;
                }
            }
            return Ok(gridlist);
        }