c# - 如果在 DropDownListFor() 中使用模型，则选择的值丢失

Question

我遇到了这个 DropDownListFor() 的问题

我有测试控制器：

model.COUNTRYNAME = "Swizerland";
        ViewBag.Selecter = new SelectList(new[]  
        { 
            new SelectListItem { Text = "USA", Value = "USA" }, 
            new SelectListItem { Text = "Swizerland", Value = "Swizerland", Selected =true}, 
             new SelectListItem { Text = "Russia", Value = "Russia" }, 

        }, "Text", "Value", model.COUNTRYNAME);

在视图中

@Html.DropDownListFor(x => Model.COUNTRYNAME , (SelectList)ViewBag.Selecter)

DropDownListFor 没有选择值，它总是选择第一个值。

怎么了？

如果我使用 DropDownList

@Html.DropDownList("COUNTRYNAME" , (SelectList)ViewBag.Selecter)

它也不起作用。

但是如果我使用

@Html.DropDownListFor("AAAAAAA" , (SelectList)ViewBag.Selecter)

它工作正常并选择第二个值！发生什么了？我不明白。

谢谢

Answer 1

试试这样：

model.COUNTRYNAME = "Swizeland";
ViewBag.Selecter = new[]  
{ 
    new SelectListItem { Text = "USA", Value = "USA" }, 
    new SelectListItem { Text = "Swizeland", Value = "Swizeland" },
    new SelectListItem { Text = "Russia", Value = "Russia" }, 
};
return View(model);

在视图中：

@Html.DropDownListFor(
    x => x.COUNTRYNAME, 
    (IEnumerable<SelectListItem>)ViewBag.Selecter
)

但更好的方法是使用视图模型：

model.SelectedCountry = "Swizeland";
model.Countries = new[]  
{ 
    new SelectListItem { Text = "USA", Value = "USA" }, 
    new SelectListItem { Text = "Swizeland", Value = "Swizeland" },
    new SelectListItem { Text = "Russia", Value = "Russia" }, 
};
return View(model);

在视图中：

@Html.DropDownListFor(x => x.SelectedCountry, Model.Countries)