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VB.NET TreeView exception

Posted on 2010-11-08
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Last Modified: 2012-05-10
I have started getting an exception thrown when trying to select a child node.

The Treeview is fillled with a company and child nodes are entered, when a specific child node is being entered it is selected with:

If CLng(prealert1.PreAlertID) = idprealert Then
  tvwPreAlert.SelectedNode = tvwNodeChild ' exception here
End If

EXCEPTION IS:
System.InvalidOperationException was unhandled
  Message=Collection was modified; enumeration operation may not execute.
 
A first guess is my logic is wrong in filling the child nodes and also selcting one in the list. If that is so then the other way to do it would be to finish filling the treeview then loop through companies/child nodes to select the required one.

If I had to loop through the treeview what would be the syntax to do that correctly?
Dim company2 As Company
			Dim tvwNodeCompany As TreeNode
			Dim tvwNodeChild As TreeNode

			For Each company2 In companyArray

				tvwNodeCompany = tvwPreAlert.Nodes.Add(company2.CompanyLedgerType + " ~ " + company2.CompanyName)

				tvwNodeCompany.Tag = company2.CompanyID.ToString()
				tvwNodeCompany.ForeColor = Color.Blue

				Dim prealert1 As PreAlertNumber
				For Each prealert1 In company2.CompanyPreAlerts
					tvwNodeChild = tvwPreAlert.Nodes(companyArray.IndexOf(company2)).Nodes.Add("Pre-alert " + prealert1.PreAlertID)
					tvwNodeChild.Tag = prealert1.PreAlertID
					If CLng(prealert1.PreAlertID) = idprealert Then
						tvwPreAlert.SelectedNode = tvwNodeChild
					End If
				Next prealert1

			Next company2

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Question by:TeDeSm
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4 Comments
 
LVL 47

Expert Comment

by:Wayne Taylor (webtubbs)
ID: 34083573
What routine are you running this code from? If it's one of the Treeview's Select events, then that code is going to be called again. What you may need to do is have a class level boolean variable and set it to True prior to setting the SelectedNode. Then in the event, check the value of that boolean variable and if True, Exit Sub.

Wayne
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Author Comment

by:TeDeSm
ID: 34085998
I am selecting a value from a combobox, see code below.
Private Sub cboPreAlert_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cboPreAlert.SelectedIndexChanged
		Dim x As Long = cboPreAlert.SelectedValue

		' Clear the TreeView
		tvwPreAlert.BeginUpdate()
		tvwPreAlert.Nodes.Clear()
		tvwPreAlert.EndUpdate()
		FilterMyTreeViewAlertNumber(x)

	End Sub

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Accepted Solution

by:
TeDeSm earned 0 total points
ID: 34091927
Found a solution to the exception, remove the erroneous code;
If CLng(prealert1.PreAlertID) = idprealert Then
  tvwPreAlert.SelectedNode = tvwNodeChild
End If

Then use the following AFTER filling the treeview that uses a function to select the required child node.

See this link:
http://www.xtremedotnettalk.com/showthread.php?t=71346


' Give treeview focus
Me.tvwPreAlert.Focus()
'look for a node with a text property value of Pre-alert + idprealert

Me.tvwPreAlert.SelectedNode = GetNode("Pre-alert " + idprealert.ToString, Me.tvwPreAlert.Nodes())
'ensure the focus set on the node
Me.tvwPreAlert.Select()
' Set the ListView's 'HideSelection' property to False
' to show selected node
Me.tvwPreAlert.HideSelection = False


Private Function GetNode(ByVal text As String, ByVal parentCollection As TreeNodeCollection) As TreeNode
Dim ret As TreeNode
Dim child As TreeNode

For Each child In parentCollection 'step through the parentcollection           
  If child.Text = text Then
    ret = child
  ElseIf child.GetNodeCount(False) > 0 Then	' if there is child items then call this function recursively
    ret = GetNode(text, child.Nodes)
  End If

  If Not ret Is Nothing Then Exit For 'if something was found, exit out of the for loop       
Next
Return ret
End Function

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Author Closing Comment

by:TeDeSm
ID: 34130136
My previous code failed due to the fact the tree was still being filled when I was trying to select a node. The exception was correct.

Waiting until the tree had finished being filled the selecting a node worked.

Remember that you are passing a string to the function which is used to check the Text value of the child node at child.Text = text.
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