ModalPopup, UpdatePanel, Javascript "Object Required" Error

[Sheldon M. Penner]

A page in my asp.net web app has a modal popup which contains a listbox that must be populated on the fly. The page contains a treeview control, right clicking a node on the treeview calls up a context menu, and if the user clicks on "Add Pretask", the popup form appears, listing items which vary depending upon which node was clicked.

The listbox is contained within an UpdatePanel which was inserted so that the list could be populated without reposting the entire page. I developed this popup, tested it, and it appeared to be working properly. I was patting myself on the back for a job well done when I happened to press a key on the computer keyboard. The app crashed with the following error message:

"Unhandled exception at line 1010, column 1 in http://localhost:55109/PPM/ScriptRe...1_Q79OAckMdH-JliDUkID4lzcsT8Bfkxn0&t=1e478eba

0x800a138f - JavaScript runtime error: Object expected"

After many unsuccessful attempts to fix this problem, I decided to recreate it on a test page, but so far I have not been able to reproduce the error.

Here is the relevant markup:


<!-- POPUP FOR ADDING PRETASKS TO SELECTED TASK -->
<a href="#" style="display:none;" onclick="javascript:return false" id="hidlinkAddPretask"
runat="server">dummy</a>

<cc1:ModalPopupExtender ID="mpePretask" runat="server" PopupControlID="pnlPretask" TargetControlID="hidlinkAddPretask"
CancelControlID="btnCancelPretask" ></cc1:ModalPopupExtender>

<aspanel ID="pnlPretask" runat="server" CssClass="popupPanel" Width="40%">

<!-- Panel within pnlPretask contains list of selected pretasks. -->
<aspanel runat="server" ID="pnlPretaskList" Visible="false">
<asp:BulletedList ID="blPretasks" runat="server">
</asp:BulletedList>
</aspanel>


<asp:HiddenField runat="server" ID="hidPostTaskID" Visible="true" />

Before <b>"<asp:Label ID="lblAddPretask" runat="server"></asp:Label>"</b> can be completed, I must:
<br /><br />

<asp:UpdatePanel ID="updPretask" runat="server" ChildrenAsTriggers="false" UpdateMode="Conditional">
<ContentTemplate>

<asp:ListBox ID="lboxPretask" runat="server" Width="80%" Height="200px"
ToolTip="Select one or more tasks that must be completed before..." AutoPostBack="false"
SelectionMode="Multiple">
</asp:ListBox>

</ContentTemplate>
</asp:UpdatePanel>

<br /><br />
<asp:UpdateProgress ID="UpdateProgress4" runat="server" DisplayAfter="0">
<ProgressTemplate>
<img src="images/progress.gif" alt="" />&nbsp;Updating...</ProgressTemplate>
</asp:UpdateProgress>

<asp:Label runat="server" ID="lblErrPretask" Font-Bold="True" ForeColor="Red" />
<br />
<asp:Button ID="btnAddAnotherPretask" runat="server" Text="Save and Add Another" />
<asp:Button ID="btnSavePretask" runat="server" Text="Save" />
<asp:Button ID="btnCancelPretask" runat="server" Text="Cancel" />
</aspanel>

The popup is called up from the server in vb:

'Repopulate lboxPretask
Dim ID As String = e.NodeClicked.Attributes("TaskID").ToString
PretaskSelectList(ID)
updPretask.Update()
mpePretask.Show()


And this routine populates the listbox:

Private Sub PretaskSelectList(ByVal TaskID As Integer)

'Populate drop down list lboxPretask with all Owner's undone, active tasks
'that are not for TaskID is not a prerequisite.

Dim strConn As String = ConfigurationManager.ConnectionStrings("PPMConnectionString").ConnectionString
Dim cnn As SqlConnection = New SqlConnection(strConn)

cnn.Open()

'Get two result sets from uspPretaskPickList
Dim sql As String = "execute dbo.uspPretaskPickList " & TaskID.ToString

Dim cmd As SqlCommand = New SqlCommand(sql, cnn)

'Result set #1 - Tasks from current Goal
Dim rdr As SqlDataReader = cmd.ExecuteReader()
Dim Itm As ListItem

With lboxPretask
.Enabled = True

.Items.Clear()

'Add a default item, #0
Itm = New ListItem("ADD NEW TASK", "0")
Itm.Attributes.Add("Style", "Font-Weight:Bold")
.Items.Add(Itm)

'Insert a separator if data reader has any records
Dim separator As New ListItem("-------------------------", "")
separator.Attributes.Add("disabled", "true")

If rdr.HasRows Then
.Items.Add(separator)
End If

'Add each member of 1st result set, using lboxPretask.Items.Add(New ListItem(TaskName, TaskID))
Do While rdr.Read
Itm = New ListItem(rdr("TaskName"), rdr("TaskID").ToString)
'Each item should be Bold.
Itm.Attributes.Add("Style", "Font-Weight:Bold")
.Items.Add(Itm)
Loop

'Add dividing line, Pretask.Items.Add("------------", "-1")
separator.Attributes.Add("disabled", "true")
.Items.Add(separator)

'Results set #2 - Tasks from other or no goal
rdr.NextResult()

'Add each member of 2nd result set, using lboxPretask.Items.Add(New ListItem(TaskName, TaskID))
Do While rdr.Read
Itm = New ListItem(rdr("TaskName"), rdr("TaskID").ToString)
.Items.Add(Itm)
Loop

End With

rdr.Close()
cnn.Close()

rdr = Nothing
cnn = Nothing

lboxPretask.ClearSelection()

End Sub




Sheldon Penner

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