谁能帮我，这两天让我感到困惑。我是Knockoutjs / viewmodel的新手。我想了解如何将数据绑定到下拉列表。下拉值需要通过API从数据库中提取，具体取决于在另一个字段中输入的值（这基本上是API返回下拉值的输入参数）。返回数据的API如下所示

[HttpPost]
    public JsonResult GetGInfo(string sNumber)
    {
        try
        {
            DSRepository dsr = new DSRepository();
            List<String> gTypeList = dsr.GetDDInfo(sNumber);
            if (gTypeList != null)
                return Json(gTypeList);
            else
                return null;    
        }
        catch (Exception e)
        {
            return null;
        }}

以下是两个字段

 // this value should be passed in to the API to retrieve the dropdown list 
 self.sNumber= ko.observable().extend({ required: { params: true, message: "Required!" } }); 
 //Dropdown list field 
 self.gType= ko.observable().extend({ required: true });

  //function for making a call to the API 
  self.getGTypes = function (data, event) {
    $.ajax({
        url: '/REQ/GetGInfo',
        type: 'POST',
        data: {
            sNumber: self.sNumber()
        },
        success: function (response) {
            if (response.length < 1)
                console.log("Record retrieved successfully");
        },
        error: function (errorThrown) {
            console.log("Error retrieving the record");
        }
    })
   }; 

UI如下所示

<div class="form-group required">
<label for="SNumber" class="control-label">SNumber:</label>
<input type="number" id="SNumber" class="form-control" data-bind="event: {change: getGTypes}, value: sNumber">
</div>

<div class="form-group required">
<label for="GType" class="control-label">GType</label>
<select id="GType" name="GType" class="form-control" data-bind="options: getGTypes, value: gType, optionsCaption: 'Select'"></select>
</div>
</div>

因此，当在SNumber字段中输入值时，即getGenoTypes会调用，我看到通过调试从API返回了数据，对于我输入的数字，我看到了下面的数据gTypeList是从API返回的

但是在下拉菜单中我什么也没看到

请帮助我，我在这里完全失踪了是什么