MVC选择列表不会在下拉列表中显示selecteditem

Question

我在Repository.cs中有以下代码来获取Timezones

public static IEnumerable<SelectListItem> GetTimeZoneList()
{
     return TimeZoneInfo.GetSystemTimeZones().Select(x => new SelectListItem()
     {
         Value = x.Id,
         Text = x.DisplayName
     });
}

我的AddEditEmployeeViewModel.cs如下：

public class AddEditEmployeeViewModel
{
   public string TimeZoneID { get; set; }
   public SelectList TimeZones { get; set; }
}

并且在ajax调用中，我填写模型值如下：

public PartialViewResult GetAddEditEmployee(string id)
{
    var model = new AddEditEmployeeViewModel();
    model.TimeZones = new SelectList(Repository.GetTimeZoneList(), "Value", "Text");
    var employee = (from e in context.tbl_users where e.eid == eid select new { e.fnamae, e.lname, e.account_status, e.preferred_timezone }).FirstOrDefault();
    if (employee == null) return PartialView("_AddEditEmployee", model);
    model.TimeZoneID = employee.preferred_timezone;
    //model.TimeZoneID will have values like India Standard Time, UTC etc.,
    //..Other properties
    return PartialView("_AddEditEmp", model);
}

即使model.TimeZoneID具有来自selectlist的匹配值，它也不会将值项保持为选中状态。我可以在SelectList中看到从DB中获取的值。参考屏幕截图

以下是view code

@Html.DropDownListFor(m => m.TimeZoneID, Model.TimeZones, "Select a Timezone", new { @class = "selectpicker", data_width = "100%", })

我犯的错误是什么？需要进行哪些更改才能从dropdownlist/selectpicker中选择项目？

Answer 1

作为一项规则，我会替换

model.TimeZones = new SelectList(
    Repository.GetTimeZoneList(), 
    "Value", 
    "Text");

与

model.TimeZones = new SelectList(
    Repository.GetTimeZoneList(), 
    "Value", 
    "Text", 
    model.TimeZoneID);

基本上，请使用overload that takes the selected value as a parameter。您也可以简单地返回您的时区对象，而不是SelectListItems的集合：

public static IEnumerable<TimeZone> GetTimeZoneList()
{
     return TimeZoneInfo.GetSystemTimeZones();
}

和

model.TimeZones = new SelectList(
    Repository.GetTimeZoneList(), 
    "ID", 
    "DisplayName", 
    model.TimeZoneID);