使用ASP.NET和C＃在ListBox中选择多个值

Question

Why "SelectedValue" selects only the first value in my multiple selection mode ?

<dt>Tags:</dt><dd>
<asp:ListBox ID="ListTag" runat="server" SelectionMode="Multiple"
    DataSourceID="SqlDataSourceTag" DataTextField="tag_name" 
    DataValueField="tag_id">
</asp:ListBox>
<asp:SqlDataSource ID="SqlDataSourceTag" runat="server" 
    ConnectionString="<%$ ConnectionStrings:db_cc %>">
</asp:SqlDataSource>
</dd>

 ListTag.SelectedValue = "Tag1"; <-- only this is selects ListTag.SelectedValue = "Tag2"; 

Answer 1

in your asp page you have this.

<asp:ListBox ID="ListTag"  runat="server" AutoPostBack="True" SelectionMode="Multiple" Width="250px">
    <asp:ListItem Selected="False" Text="Tag-1" Value="1">Tag - 1</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-2" Value="2">Tag - 2</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-3" Value="3">Tag - 3</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-4" Value="4">Tag - 4</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-5" Value="5">Tag - 5</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-6" Value="6">Tag - 6</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-7" Value="7">Tag - 7</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-8" Value="8">Tag - 8</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-9" Value="9">Tag - 9</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-10" Value="10">Tag - 10</asp:ListItem>
</asp:ListBox>

then in your cs(Code Behind) in the event that you want you have this.

  for (int i = 0; i < lsBox.Items.Count; i++)
        {
            var item = lsBox.Items[i];
            string[] selectecvalues = new string[] { "1", "3", "6", "9" };

            if (selectecvalues.Contains(item.Value)) // or item.Text  if you like
            {
                lsBox.Items[i].Selected = true;
            }
        }

that will result in Tags 1,3,6,9 selectd