从 API MVC C# 填充下拉列表选项值

Question

我有一个在下拉值更改时调用的API。它返回 JSON 结果，我想从这些 JSON 结果中更新另一个下拉列表，但我的 Jquery 中不断出现错误

剃须刀视图页面

<div class="form-group">
      @Html.LabelFor(model => model.CustomerProfile.Country, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
           @Html.DropDownListFor(model => model.CustomerProfile.Country, Model.CountryList, htmlAttributes: new { @id = "profileCountry", @class = "form-control col-md-2" , @onchange = "FillState()" })
        </div>
</div>
<div class="form-group">
    @Html.LabelFor(model => model.CustomerProfile.State, htmlAttributes: new { @class = "control-label col-md-2" })
     <div class="col-md-10">
       @Html.DropDownListFor(model => model.CustomerProfile.State, new SelectList(Enumerable.Empty<SelectListItem>(), "StateFullName", "StateFullName"),
                  "Select State",
                  htmlAttributes: new { @id = "profileState", @class = "form-control col-md-2" })
     </div>
</div>

Jquery 脚本

<script>
  function FillState() {
      var countryParam = $('#profileCountry').val();
    $.ajax({
        url: '/api/CountryToState/FillState',
        type: "GET",
        dataType: "JSON",
        data: { country: countryParam},
        success: function (states) {
            $("#profileState").html(""); // clear before appending new list
            $.each(states, function (i, statetest) {
                $("#profileState").append(
                    $('<option></option>').val(statetest.StateFullName).html(statetest.StateFullName));
            });
        }
    });
  }
</script>

接口代码

 [System.Web.Http.HttpGet]
        public ActionResult FillState(string country)
        {
            var states = _context.CountryToState.Where(c => c.CountryName == country);
            return new JsonResult()
            {
                Data = states,
                JsonRequestBehavior = JsonRequestBehavior.AllowGet
            };
        }

国与国模型

 public class CountryToState
    {
        [Column("lngStateID")]
        [Key]
        public Int32 StateID { get; set; }
        [Column("strCountry")]
        public string CountryName { get; set; }
        [Column("strStateFullName")]
        public string StateFullName { get; set; }
}

它一直给我一个错误 无法读取 null 的属性"状态全名"。 成功函数中返回的状态有 36 行，每行都有状态全名。为什么它是空的。我该如何解决这个问题。我希望值和文本在下拉列表中是状态全名。

我不正确地理解每个函数

Console.Log(状态( 显示以下内容：

ContentEncoding: null, ContentType: null, Data: Array(36), JsonRequestBehavior: 0, MaxJsonLength: null, …}
ContentEncoding: null
ContentType: null
Data: (36) [{…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}]
JsonRequestBehavior: 0
MaxJsonLength: null
RecursionLimit: null
__proto__: Object

Answer 1

我查看了您的代码，我认为错误源于 ajax 成功函数

$.ajax({
    url: '/api/CountryToState/FillState',
    type: "GET",
    dataType: "JSON",
    data: { country: countryParam},
    success: function (states) {
        $("#profileState").html(""); // clear before appending new list
        $.each(states, function (i, statetest) {
            $("#profileState").append(
                $('<option></option>').val(statetest.StateFullName).html(statetest.StateFullName));
        });
    }
});

在上面的代码中，我认为成功回调中的状态参数具有这样的结构：

{
  ContentEncoding: ...
  ContentEncoding: ...
  ContentType: ...
  Data: (36) [{…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, 
             {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, 
             {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}]
  JsonRequestBehavior: ...
  MaxJsonLength: ...
  RecursionLimit: ...
}

所以你需要在状态中做一个循环。数据而不是状态：

$.each(states.Data, function (i, statetest) {
            $("#profileState").append(
                $('<option></option>').val(statetest.StateFullName).html(statetest.StateFullName));
        });