C# @Html.dropdownlist对于使用ViewBag SelectedListItem，不显示所选项目

我的代码如下：

控制器：

foreach (Employee engineer in engineers)
{                       
       if (!model.Customer.PrimaryEngineerId.Equals(engineer.EmployeeId)) 
       {
            engineersListPrimary.Add(new SelectListItem { Text = engineer.FirstName + ' ' + engineer.LastName, Value = engineer.EmployeeId, Selected = false});
       }
       else
       {
            engineersListPrimary.Add(new SelectListItem { Text = engineer.FirstName + ' ' + engineer.LastName, Value = engineer.EmployeeId, Selected = true });
       }                 
}
ViewBag.engineersListPrimary = engineersListPrimary;
return View(model);

@Html.DropDownListFor(m => m.Customer.PrimaryEngineer, (IEnumerable<SelectListItem>)ViewBag.engineersListPrimary, new { style = "width:100%;"})

查看：

foreach (Employee engineer in engineers)
{                       
       if (!model.Customer.PrimaryEngineerId.Equals(engineer.EmployeeId)) 
       {
            engineersListPrimary.Add(new SelectListItem { Text = engineer.FirstName + ' ' + engineer.LastName, Value = engineer.EmployeeId, Selected = false});
       }
       else
       {
            engineersListPrimary.Add(new SelectListItem { Text = engineer.FirstName + ' ' + engineer.LastName, Value = engineer.EmployeeId, Selected = true });
       }                 
}
ViewBag.engineersListPrimary = engineersListPrimary;
return View(model);

@Html.DropDownListFor(m => m.Customer.PrimaryEngineer, (IEnumerable<SelectListItem>)ViewBag.engineersListPrimary, new { style = "width:100%;"})

@Html.DropDownListFor（m=>m.Customer.PrimaryEngineer，（IEnumerable）ViewBag.engineersListPrimary，新{style=“width:100%；”}）

在搜索了很多并尝试了很多不同的方法之后，我无法打印所选的值

问题：

foreach (Employee engineer in engineers)
{                       
       if (!model.Customer.PrimaryEngineerId.Equals(engineer.EmployeeId)) 
       {
            engineersListPrimary.Add(new SelectListItem { Text = engineer.FirstName + ' ' + engineer.LastName, Value = engineer.EmployeeId, Selected = false});
       }
       else
       {
            engineersListPrimary.Add(new SelectListItem { Text = engineer.FirstName + ' ' + engineer.LastName, Value = engineer.EmployeeId, Selected = true });
       }                 
}
ViewBag.engineersListPrimary = engineersListPrimary;
return View(model);

@Html.DropDownListFor(m => m.Customer.PrimaryEngineer, (IEnumerable<SelectListItem>)ViewBag.engineersListPrimary, new { style = "width:100%;"})

所选值不会显示在视图中使用的下拉列表中

调试后，我已检查engineersListPrimary是否正确填充（正确插入Selected=true行），因此问题必须保留在视图中

---

有什么建议吗？？谢谢你的回答

试试这样的东西

@Html.DropDownListFor(model => model.SelectedID, new SelectList(model.PrimaryEngineer, "Value", "Text"), "optionalLabel",  new { style = "width:100%;"})

---

问题在于这个表达式：

m => m.Customer.PrimaryEngineer

DropDownListFor期望此lambda提供您正试图通过此输入控件设置的属性。在您的情况下，这不是

m.Customer.PrimaryEngineer

，而是

m.Customer.PrimaryEngineerId

，因此应该解决它：

m => m.Customer.PrimaryEngineerId

---

还请注意，在使用DropDownList for时，不需要设置列表项的

Selected

属性，因为此帮助程序可以根据提供的模型值派生所选项。

我看到的最佳方法是使用

SelectList（）

来执行此操作

用以下代码替换foreach循环代码，就可以开始了：

ViewBag.engineersListPrimary = new SelectList(engineers,
                                             "EmployeeId",
                                             "FirstName",
                                             model.Customer.PrimaryEngineerId);
return View(model);

鉴于：

@Html.DropDownListFor(m => m.Customer.PrimaryEngineer, 
                           ViewBag.engineersListPrimary as SelectList, 
                           new { style = "width:100%;"})

MSDN文件：

---

参见

我假设

m=>m.Customer.PrimaryEngineer

后面缺少的逗号只是问题中的一个输入错误。如果您在

@Html.DropDownListFor

行上放置断点，则

ViewBag.engineersListPrimary

是否仍然正确？是的，逗号在我的代码中，我已将其更正为发布的代码。

ViewBag.engineersListPrimary

正确地填充了所选的=真值。但正如@Andrei所说，我必须将

m=>m.Customer.PrimaryEngineer

更改为

m=>m.Customer.primaryengineerinid

，并自动填充所选值。谢谢你的回答！是的，它有效！即使ViewBag没有将属性Selected设置为true，它也会在DropDownList for中正确选择工程师。我想在内部将值设置为Selected=true，否？谢谢你的回答@Alvykun，坦白说，我还没有检查过。但是你的假设看起来很有可能me@Alvykun与其如此混乱和重复使用

SelectList

class，还不如查看我的帖子以获得更多的澄清