Question

If I have the following ListView, how can I attach a SelectedIndexChanged event listener to the DropDownList so I can perform a command on the respective object? Imagine I have a list of new users and I want to add them to a usergroup by selecting the group from the DropDownList.

<asp:ListView ID="NewUsers" runat="server" DataSourceID="NewUsersSDS" DataKeyNames="ID">
    <LayoutTemplate>
        <asp:Table ID="groupPlaceholder" runat="server"><asp:TableRow></asp:TableRow></asp:Table>
    </LayoutTemplate>
    <GroupTemplate>
        <asp:TableCell ID="itemPlaceholder" runat="server"></asp:TableCell>
    </GroupTemplate>
    <ItemTemplate>
        <asp:Table ID="NewUsersTable" runat="server" Width="32%" CssClass="inlineTable">
            <asp:TableRow>
                <asp:TableCell Width="100px"><%# Eval("FullName").ToString.Trim()%></asp:TableCell>
                <asp:TableCell>
                    <asp:HiddenField ID="RowIndex" runat="server" Value="<%# Container.DisplayIndex %>" />
                    <asp:DropDownList ID="UserGroupSelect" runat="server" DataSourceID="UserGroupSelectSDS" DataValueField="ID" DataTextField="UserGroup"
                        OnSelectedIndexChanged="UserGroupSelect_SelectedIndexChanged" AutoPostBack="True">
                    </asp:DropDownList>
                </asp:TableCell>
            </asp:TableRow>
        </asp:Table>
    </ItemTemplate>
</asp:ListView>

I’ve been having issues accessing controls inside of __View controls. I read in a few places that you could access them by NewUsers.FindControl([ControlID as String]) but this doesn’t seem to be working for me. I guess this is what’s called a dynamic control? Not really sure, feeling a bit lost.

As always, your help is greatly appreciated. 😉

Additional Info / Code

'Now working code, thanks to James :)
Protected Sub ItemBind(ByVal sender As Object, ByVal e As ListViewItemEventArgs) Handles NewUsers.ItemDataBound
    Dim lv As ListView = DirectCast(sender, ListView)
    If e.Item.ItemType = ListViewItemType.DataItem Then
        lv.DataKeys(e.Item.DataItemIndex).Value.ToString() 'get the datakey
    End If
End Sub
    Protected Sub UserGroupSelect_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
    Dim RowIndex As Integer = CInt(DirectCast(DirectCast(sender, DropDownList).Parent.FindControl("RowIndex"), HiddenField).Value)
    Dim pk As Integer = CInt(NewUsers.DataKeys(RowIndex)("ID"))
    Try
        MessageBox("Update key " + pk.ToString, "Update Key") 'Custom js "alert" box function
    Catch ex As Exception
        MessageBox("Something went wrong, is the update key empty?")
    End Try
End Sub

Answer 1

To access controls in a ListView (or any databound control), you need to use FindControl on the item/row:

ListViewItem item = ListView1.Items[0];
if (item != null)
{
    DropDownList ddl = item.FindControl("DropDownList1") as DropDownList;
    if (ddl != null)
    {
        string value = ddl.SelectedValue;
    }
}

As for attaching a SelectedIndexChanged event, you can do it like this:

<ItemTemplate>
    <asp:DropDownList ID="DropDownList1" runat="server" 
        AutoPostBack="true" 
        OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged">
    </asp:DropDownList>
    <asp:HiddenField ID="HiddenField1" runat="server" Value='<%# Container.DisplayIndex %>' />
</ItemTemplate>

Code-behind:

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
    int rowIndex = Convert.ToInt32(((HiddenField)((DropDownList)sender).Parent.FindControl("HiddenField1")).Value);

    ListViewItem item = ListView1.Items[rowIndex];
    if (item != null)
    {
        //your logic here
    }        
}

To retrieve a datakey:

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
    int rowIndex = Convert.ToInt32(((HiddenField)((DropDownList)sender).Parent.FindControl("HiddenField1")).Value);

    int pk = (int)ListView1.DataKeys[rowIndex]["PrimaryKey"];     
}