通过另一个下拉列表中的值填充下拉列表ASP.NET

Question

根据另一个下拉列表中定义的值，将下拉列表获取到数据绑定时遇到了一些麻烦。

Protected Sub CategoryDDL_SelectedIndexChanged(sender As Object, e As EventArgs) Handles CategoryDDL.SelectedIndexChanged 
    qaDDL.Items.Clear() 
    qaDDL.Items.Insert(0, New ListItem("(New Question)")) 

    If CategoryDDL.SelectedValue = "(New Category)" Then 
     CategoryName.Text = Nothing 
    Else 
     Dim filter As String = "categoryID = '" + CategoryDDL.SelectedValue.ToString() + "'" 
     Dim dv As DataView = CType(SqlDataSource1.Select(DataSourceSelectArguments.Empty), DataView) 
     dv.RowFilter = filter 
     For Each drv As DataRowView In dv 
      CategoryName.Text = drv("Name").ToString() 
     Next 

我已经试过什么类同材料填充一个文本框，但我不知道怎么用这个数组。

dv = CType(SqlDataSource2.Select(DataSourceSelectArguments.Empty), DataView) 
     For Each drv As DataRowView In dv 
      qaDDL.Items.Insert(drv("placement").ToString(), drv("Question").ToString()) 
     Next 
    End If 
End Sub 

我也尝试过使用一个简单的数据绑定用asp：由DataSourceID的

qaDDL.Databind() 

这里的页面的样子连接下拉列表。

<asp:DropDownList runat="server" ID="CategoryDDL" DataSourceID="SqlDataSource1" Width="300px" DataTextField="Name" DataValueField="categoryID" AppendDataBoundItems="True" AutoPostBack="True" > 
      <asp:ListItem Value="(New Category)">(New Category)</asp:ListItem> 
     </asp:DropDownList> 
     <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings%>" SelectCommand="SELECT categoryID, Name, placement FROM FAQ_category ORDER BY placement"></asp:SqlDataSource> 

<asp:DropDownList runat="server" ID="qaDDL" Width="300px" AppendDataBoundItems="True" AutoPostBack="True" DataSourceID="SqlDataSource2" DataTextField="Question" DataValueField="faqID"> 
      <asp:ListItem Value="(New Question)">(New Question)</asp:ListItem> 
     </asp:DropDownList> 
     <asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ ConnectionStrings%>" SelectCommand="SELECT faqID, categoryID, Question, Answer FROM FAQ WHERE (categoryID = @categoryID) ORDER BY placement"> 

那么做这类任务的最好方法是什么？

Answer 1

最好的办法可能是主观的，但我建议最简单的方式是使用AjaxControlToolkit的CascadingDropDownList扩展的控制，因为它可以节省您的回传，很多工作已经为你做。