当我在DropDownList中选择一个项目时，Selected未设置为true

Question

我见过this question，但不清楚以下内容：

我有一个exec sp_executesql N'SELECT [Limit2].[C1] AS [C1] FROM ( SELECT TOP (1) CASE WHEN ([Project2].[C1] IS NULL) THEN cast(0 as bigint) ELSE [Project2].[Percentage] END AS [C1] FROM ( SELECT 1 AS X ) AS [SingleRowTable1] LEFT OUTER JOIN (SELECT TOP (1) [Project1].[Percentage] AS [Percentage], cast(1 as tinyint) AS [C1] FROM ( SELECT [Extent1].[Amount] AS [Amount], [Extent1].[Percentage] AS [Percentage] FROM [dbo].[Discount] AS [Extent1] WHERE [Extent1].[Amount] <= @p__linq__0 ) AS [Project1] ORDER BY [Project1].[Amount] DESC ) AS [Project2] ON 1 = 1 ) AS [Limit2]',N'@p__linq__0 bigint',@p__linq__0=15000 ，我是这样填充的：

SelectListItem

在我看来，它是这样显示的：

MySelectList.Insert(0, new SelectListItem { Text = "Text0", Value = "0" });
MySelectList.Insert(1, new SelectListItem { Text = "Text1", Value = "1" });

如果我选择 Text0 并将模型发布到控制器，则MyId将包含所选的值，这是完美的。

但是当我浏览@Html.DropDownListFor(m => m.MyId, Model.MySelectList, new { @class = "form-control" }) 时，列表中的任何项目的MySelectList值都未设置为Selected：

我知道我可以使用MyId查找选定的值，但是当用户从下拉菜单中选择一项并发布表格时，有什么方法可以将true设置为Selected？ >

Answer 1

这并不意味着框架会自动对其进行更新。当您检查HTTP请求时，您会注意到只有MyId的值被传输。当通过模型绑定器重建目标视图模型时，根本不会填充MySelectList，当您在其中看到一些数据时，这可能是因为您在请求后再次填充了它。

您当然可以轻松地自己执行更新：

var selectedItem = Model.MySelectList.FirstOrDefault(x => x.Value == Model.MyId);
if (selectedItem != null)
{
    selectedItem.Selected = true;
}

问题是，它是否对您的进一步处理有所帮助。