[RESOLVED] [2005] Speeding up TreeView.

[Tinbeard]

I have a treeView in my application that displays the available ebay categories, as you can imagine this is quite sizeable, around 2500 dataTable rows.

The problem I have is when a parent category is expanded there is a delay (not massive but enough to be annoying) while the application goes through the dataTable and pulls out the relevent sub categories and any associated child items.

I've not done a great deal with treeviews so the method I'm using to populate it may not be the best.

If anyone could point me in the right direction for eliminating or at least minimising the delay .....

The code for the treeview is as follows:

Public Class Categories
 
    Dim dt As DataTable
    Dim dr As DataRow
    Dim tn As TreeNode
 
    Private Sub Categories_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        dt = Main.dtCats
        'if the category list is still being downloaded show the please wait message.
        lblMessage.Visible = True
        trvCats.ImageList = ImageList1
    End Sub
 
    Private Sub Categories_Shown(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Shown
        If dt.Rows.Count > 1 Then
            loadLIst()
        End If
    End Sub
 
    '///
    'This method loads the initial top level parents and any associated child items
    '///
    Public Sub loadList()
        'Hide the please wait message
        lblMessage.Visible = False
        For Each dr In dt.Rows
            If dr("level") = "1" Then
                tn = New TreeNode
                tn.Text = dr("name")
                tn.Name = dr("CatID")
                'check if the node is a leaf category, if so set the images required
                If dr("leaf") Then
                    tn.ImageIndex = 2
                    tn.SelectedImageIndex = 2
                End If
                trvCats.Nodes.Add(tn)
                AddChildNodes(tn)
            End If
        Next
    End Sub
 
    '///
    'This method add the child nodes to the parent node
    '///
    Private Sub AddChildNodes(ByVal tn As TreeNode)
        If tn.Nodes.Count = 0 Then
            Dim childNode As TreeNode
            For Each dr As DataRow In dt.Rows
                'find the rows that have the same parent ID but not the same name
                'as this will add a duplicate of the parent category to the list
                If dr("ParentID") = tn.Name AndAlso dr("name") <> tn.Text Then
                    childNode = New TreeNode
                    childNode.Text = dr("name")
                    childNode.Name = dr("CatID")
                    'if the category is a leaf then add the appropriate image
                    If dr("leaf") Then
                        childNode.ImageIndex = 2
                        childNode.SelectedImageIndex = 2
                    End If
                    'add the node to the collection
                    tn.Nodes.Add(childNode)
                End If
            Next
        End If
    End Sub
 
    Private Sub trvCats_AfterCollapse(ByVal sender As Object, ByVal e As System.Windows.Forms.TreeViewEventArgs) Handles trvCats.AfterCollapse
        'node has been collapsed so reset the image displayed
        e.Node.ImageIndex = 0
    End Sub
 
    Private Sub trvCats_AfterSelect(ByVal sender As Object, ByVal e As System.Windows.Forms.TreeViewEventArgs) Handles trvCats.AfterSelect
        'get the id of the selected node
        tn = e.Node
        AddChildNodes(tn)
        For Each node As TreeNode In tn.Nodes
            AddChildNodes(node)
        Next
    End Sub
 
    Private Sub trvCats_BeforeExpand(ByVal sender As Object, ByVal e As System.Windows.Forms.TreeViewCancelEventArgs) Handles trvCats.BeforeExpand
        'get the id of the selected node
        tn = e.Node
        'node is being expanded so change the image displayed
        tn.ImageIndex = 1
        AddChildNodes(tn)
        For Each node As TreeNode In tn.Nodes
            AddChildNodes(node)
        Next
    End Sub
End Class