BUG: TreeView: Nodes Count Property Limited to 32767

• Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, version 5.0
• Microsoft Visual Basic Professional and Enterprise Editions for Windows, version 4.0

SYMPTOMS

The Count property of the Nodes collection for a TreeView control returns an incorrect value if you add more than 32767 nodes to the TreeView. The Index property of a Node object also returns an incorrect value for the same reason. If you add more than 65535 nodes, the TreeView's scrollbar may disappear and the TreeView may experience redraw problems.

NOTE: In Visual Basic 4.0, you may receive the following error if you attempt to add more than 32767 nodes to a TreeView control:

   Run-time error '7':
   Out of memory

CAUSE

The Count property of the Nodes collection and the Index property of a Node object are limited to Integer values. If you add an additional node beyond 32767 nodes, the Count property of the Nodes collection returns a value of -32768 (instead of 32768). Adding another node to the TreeView results in the Count property returning a value of -32767, and so on. After adding 65536 nodes, the Count property reverts back to a value of 0. When this occurs, the TreeView control appears empty with no scrollbars because it thinks there are no actual nodes to display.

RESOLUTION

It is not recommended that you add more than 32767 nodes to a TreeView control. If you need more than 32767 nodes, you should consider using multiple TreeView controls or a control more suited for larger amounts of data.

If you would like to maintain more than 32767 nodes using Visual Basic versions after version 4.0 in a TreeView control, you should keep the following in mind:

- Performance will become extremely slow as you add more and more nodes.

- Do not add more than 65535 nodes.

- Use the SendMessage API to obtain the true node count. Alternately, you

  can use a module- or public-level variable to keep track of how many
  nodes are in the TreeView. Each time you add or remove a node, increment
  or decrement the variable by one. This is necessary if you need to
  determine the count of nodes because the Count property of the Nodes
  collection will not return the correct value.

  property is 32767 for node 32767 but is -32768 for node 32768.

  the Nodes collection. For example:

     TreeView1.Nodes(40000) refers to node 40000.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. We are researching this bug and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

Steps to Reproduce Behavior

1. Create a new Standard EXE project in Visual Basic. Form1 is created by default.

2. Click Components on the Project menu and select "Microsoft Windows Common Controls."

3. Add a TreeView, CommandButton, and a TextBox to Form1.

4. Copy and paste the following code to the code window of Form1:

         Option Explicit
   

         Private Const TVM_GETCOUNT = &H1105&
         Private Declare Function SendMessage Lib "user32" Alias
           "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal _
           wParam As Long, lParam As Any) As Long
   
         Private Sub Command1_Click()
            Dim lngCnt As Long
            Dim nodX As Node
            Set nodX = TreeView1.Nodes.Add(, , "R", "Root")
            For lngCnt = 1 To 32766
               Set nodX = TreeView1.Nodes.Add("R", tvwChild, "C" & lngCnt, _
                  "Child " & lngCnt)
               If lngCnt Mod 1000 = 0 Then 'refresh
                   Text1.Text = lngCnt
                   DoEvents
               End If
            Next
            Text1.Text = TreeView1.Nodes.Count
            MsgBox "Nodes count: " & TreeView1.Nodes.Count
            Set nodX = TreeView1.Nodes.Add("R", tvwChild, "C" & lngCnt, _
               "Child " & lngCnt)
            MsgBox "Nodes count: " & TreeView1.Nodes.Count
            MsgBox "Actual Node Count: " & SendMessage(TreeView1.hwnd, _
                   TVM_GETCOUNT, 0, ByVal 0)
         End Sub
   
   

5. Press the F5 key to start the project.

   several minutes to complete on a Pentium class computer.

   Result: After 32767 nodes are added to the TreeView (1 for the Root +
   32766 child nodes), you receive a message box indicating 32767 nodes in
   the TreeView. This is correct. However, the second message box
   incorrectly states there are -32768 nodes after one more node is added
   to the TreeView. The third message box displays the correct node count.