无法在列表框中选择多个项目

Question

I have a ListBox and DropDownList in GridView EditItemTemplate . On rowEditing , I want to select all the items in ListBox . Below is my code:

string categories = (e.Row.FindControl("lblCategoryID") as Label).Text;          
ListBox lbx = (ListBox)e.Row.FindControl("lbSelectedCategory");
DropDownList drp = (DropDownList)e.Row.FindControl("drpCat");
List<string> TagIds = categories.Split(',').ToList();
lbx.SelectionMode = ListSelectionMode.Multiple;
foreach (string s in TagIds)
{
     ListItem li = drp.Items.FindByValue(s);
     lbx.Items.Add(li);
}

Here the items gets added into the Listbox .

But when I try to select the multiple items,

for (int i = 0; i < lbx.Items.Count; i++)
{
     lbx.Items[i].Selected = true;
}

I get error :

cannot select multiple items in a dropdownlist.

Aspx:

<EditItemTemplate>
   <asp:Label ID="lblCategoryID" Text='<%# Bind("tag_id") %>' runat="server"></asp:Label>
   <asp:ListBox ID="lbSelectedCategory" Visible="false" Width="150px" runat="server"
         SelectionMode="Multiple" CssClass="chosen-select"></asp:ListBox>
   <asp:DropDownList ID="drpCat" AutoPostBack="true"
         OnSelectedIndexChanged="drpCat_SelectedIndexChanged" CssClass="chosen-select" runat="server">
   </asp:DropDownList>
</EditItemTemplate>

Can anyone help me solving this Issue?

Answer 1

与其在下拉列表中查找行并将相同的行添加到ListBox中，不如尝试从下拉列表中创建一个与ListItem具有相同值的新ListItem并添加它。