Why can't I find the control?

uczxnvdrlf · Apr 28, 2012

Hi, I am building a DataGrid with dynamic columns added to the grid in Page_Init. As part of this, the EditItemTemplate is loaded into the DataGrid from a separate .ascx file via the Page.LoadTemplate method. My problem is that I am having difficulties finding the server controls within this dynamically-added EditItemTemplate, (which I need to do to change their properties and add events dynamically). On a non-dynamic TemplateColumn, I would simply use the following code to find a server control in an EditItemTemplate: sub dg_ItemDataBound(sender as object, e as DataGridItemEventArgs) If (e.Item.ItemType = ListItemType.EditItem) then Dim lbtExampleLinkButton as LinkButton = e.Item.FindControl("lbtExampleLinkButton") lbtExampleLinkButton.Text="Text property dynamically changed in dg_ItemDataBound" end if end sub But when I try to do this for my dynamic TemplateColumn, it doesn't work (neither in dg_ItemDataBound, nor in dg_ItemCreated), and I get the following error message: System.NullReferenceException: Object reference not set to an instance of an object Can anyone tell me how to locate these server controls in a dynamic Template Column? Thanks, JON ++++++++++++++++++++++++++++++++++++++++++++++++++ ++++ MAIN DATAGRID PAGE (the EditItemTemplate is in a separate ascx file, see below): ++++++++++++++++++++++++++++++++++++++++++++++++++ ++++ <%@ Page Language="VB" Debug="true" %> <%@ Import Namespace="System.Data" %> <%@ Import Namespace="System.Data.Oledb" %> <script language="VB" runat="server"> Dim objConn as New OleDbConnection ( ConfigurationSettings.AppSettings("ConnectionString") ) Dim ds as Dataset = New DataSet() Dim objAdapter as New OleDbDataAdapter ( "SELECT * FROM tblItems WHERE ItemID = 1;", objConn ) Sub Page_Init(sender as object, e as eventargs) Dim tc1 As New TemplateColumn() tc1.HeaderTemplate = New DataGridTemplate(ListItemType.Header, "Column1") tc1.ItemTemplate = New DataGridTemplate(ListItemType.Item, "Column1") tc1.EditItemTemplate = Page.LoadTemplate("Example_EditItemTemplate.ascx") tc1.FooterTemplate = New DataGridTemplate(ListItemType.Footer, "Column1") dg.Columns.Add(tc1) End sub Sub Page_Load(sender as object, e as eventargs) objConn.Open() objAdapter.Fill(ds, "tblItems") dg.DataSource = ds dg.DataMember = "tblItems" If Not Page.IsPostBack Then dg.Databind() End If End Sub sub dg_edit(sender as object, e as DataGridCommandEventArgs) dg.edititemindex = e.item.itemindex dg.databind() end sub sub dg_cancel(sender as object, e as DataGridCommandEventArgs) dg.edititemindex = -1 dg.databind() end sub sub dg_update(sender as object, e as DataGridCommandEventArgs) 'Put an update function here end sub sub dg_command(sender as object, e as DataGridCommandEventArgs) 'Do something later here end sub sub dg_ItemCreated(sender as object, e as DataGridItemEventArgs) 'can't find lbtExampleLinkButton in dg_ItemDataBound or here either end sub sub dg_ItemDataBound(sender as object, e as DataGridItemEventArgs) If (e.Item.ItemType = ListItemType.EditItem) then Dim lbtExampleLinkButton as LinkButton = e.Item.FindControl("lbtExampleLinkButton") lbtExampleLinkButton.Text="Text property dynamically changed in dg_ItemDataBound" '************************************************* ************************* 'Above line gets following error: 'System.NullReferenceException: Object reference not set to an instance of an object '************************************************* ************************* AddHandler lbtExampleLinkButton.Click, AddressOf DoSomething end if end sub sub DoSomething(sender as object, e as EventArgs) Response.Write("written in Sub DoSomething") end sub Private Class DataGridTemplate Implements ITemplate Dim templateType As ListItemType Dim columnName As String Sub New(ByVal type As ListItemType, ByVal ColName As String) templateType = type columnName = ColName End Sub Sub InstantiateIn(ByVal container As Control) Implements ITemplate.InstantiateIn Dim lc As New Literal() Select Case templateType Case ListItemType.Header lc.Text = "Header" container.Controls.Add(lc) Case ListItemType.Item lc.Text = "Item " & columnName container.Controls.Add(lc) Case ListItemType.EditItem Dim tb As New TextBox() tb.Text = "" container.Controls.Add(tb) Case ListItemType.Footer lc.Text = "Footer" container.Controls.Add(lc) End Select End Sub End Class </script> <html><body> <form runat="server" name="form1" id="form1"> <asp

ataGrid id="dg" runat="server" HeaderStyle-BackColor="#cccc99" FooterStyle-BackColor="#cccc99" ItemStyle-BackColor="#ffffff" AlternatingItemStyle-Backcolor="#cccccc" AutoGenerateColumns="False" ShowFooter="True" OnEditCommand="dg_edit" OnCancelCommand="dg_cancel" OnUpdateCommand="dg_update" OnItemCommand="dg_command" OnItemCreated="dg_ItemCreated" OnItemDataBound="dg_ItemDataBound" > <Columns> <asp:editcommandcolumn HeaderText="EDIT" edittext="Edit" CancelText="Cancel" UpdateText="Save" /> </Columns> </asp:dataGrid> </form> </body></html> __________________________________________________ ____________________________ CODE FOR "Example_EditItemTemplate.ascx": <%@ Control Language="VB" %> ItemTitle: <asp:Textbox id="tbItemTitle" runat="server" /> ItemRating: <asp:TextBox id="tbItemRating" runat="server" /> <asp:LinkButton id="lbtExampleLinkButton" runat="server" Text="ExampleLinkButton" /> <asp:Button id="btExampleButton" runat="server" Text="ExampleButton" />

Why can't I find the control?

uczxnvdrlf

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