BUG: TreeView Problems with CheckBoxes

• Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, version 6.0

SYMPTOMS

After setting the Treeview control's Checkbox's property to True, selecting the CheckBox on a child node can return the incorrect state of the CheckBox. The value returned is inconsistent depending upon whether the CheckBox is selected or the label is selected. Also, clicking the CheckBox does not fire the NodeClick event; it only fires the Click event of the TreeView.

RESOLUTION

Use Win32 API calls instead of setting the Checkboxes property to True. See the MORE INFORMATION section below for more details.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

The Checkboxes property has been added to the Treeview control that is shipped with Visual Basic 6.0.

Steps to Reproduce Behavior

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



2. From the Project menu, choose Components, and select "Microsoft Windows Common Controls 6.0."



3. Place a TreeView control on Form1.



4. Add the following to the code window of Form1:

   
         Private Sub Form_Load()
            Const TVS_CHECKBOXES = &H100
            Const GWL_STYLE = (-16)
   
            Dim CurStyle As Long
            Dim Result As Long
   
            Dim nodX As Node
            Set nodX = TreeView1.Nodes.Add(, , "R", "Root")
            Set nodX = TreeView1.Nodes.Add("R", tvwChild, "C1", "Child 1")
            Set nodX = TreeView1.Nodes.Add("R", tvwChild, "C2", "Child 2")
            Set nodX = TreeView1.Nodes.Add("R", tvwChild, "C3", "Child 3")
            Set nodX = TreeView1.Nodes.Add("R", tvwChild, "C4", "Child 4")
            nodX.EnsureVisible
            TreeView1.Checkboxes = True
   
            TreeView1.Style = tvwTreelinesText   ' Style 4.
            TreeView1.BorderStyle = vbFixedSingle
         End Sub
   
         Private Sub TreeView1_NodeClick(ByVal Node As MSComctlLib.Node)
            ' This code never gets executed
            Debug.Print "NodeClick: "; TreeView1.SelectedItem.Checked
         End Sub
   
         Private Sub TreeView1_Click()
            Debug.Print "Click: "; TreeView1.SelectedItem.Checked
         End Sub 




5. Save the project and run it.



6. Click one of the child node CheckBoxes and look at the checked state in the immediate window. Note that the checked state is False even though the CheckBox is selected.
   
   NOTE: The checked property should be consistent with the state of the CheckBox of the node. This should also be available to the NodeClick event.



7. Click the label of one of the child nodes and note that the checked state is displayed properly.



8. To work around this bug, use the Win32 API call SetWindowLong to manually set the CheckBox style of the TreeView. In order for this to function properly, set the LabelEdit property to tvwManual. Following these steps allows the NodeClick event to fire and the checked property will be consistent with the state of the CheckBox of the node.



9. Return to the design environment and modify the code in the Form1 module to match the following (you can also delete the existing code and add this):

   
         Private Declare Function GetWindowLong Lib "user32" Alias _
          "GetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long) As Long
   
         Private Declare Function SetWindowLong Lib "user32" Alias _
          "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, _
          ByVal dwNewLong As Long) As Long
   
         Private Sub Form_Load()
            Const TVS_CHECKBOXES = &H100
            Const GWL_STYLE = (-16)
   
            Dim CurStyle As Long
            Dim Result As Long
   
            Dim nodX As Node
            Set nodX = TreeView1.Nodes.Add(, , "R", "Root")
            Set nodX = TreeView1.Nodes.Add("R", tvwChild, "C1", "Child 1")
            Set nodX = TreeView1.Nodes.Add("R", tvwChild, "C2", "Child 2")
            Set nodX = TreeView1.Nodes.Add("R", tvwChild, "C3", "Child 3")
            Set nodX = TreeView1.Nodes.Add("R", tvwChild, "C4", "Child 4")
            nodX.EnsureVisible
   
            TreeView1.LabelEdit = tvwManual
            TreeView1.Style = tvwTreelinesText   ' Style 4.
            TreeView1.BorderStyle = vbFixedSingle
            CurStyle = GetWindowLong(TreeView1.hwnd, GWL_STYLE)
            Result = SetWindowLong(TreeView1.hwnd, GWL_STYLE, _
                     CurStyle Or TVS_CHECKBOXES)
         End Sub
   
         Private Sub TreeView1_NodeClick(ByVal Node As MSComctlLib.Node)
            Debug.Print TreeView1.SelectedItem.Checked
         End Sub 




10. Save and run the project again. Repeat steps 6 - 7 and observe that the incorrect behavior no longer occurs. NOTE: The LabelEdit property needs to be set to tvwManual or the workaround will not be effective.

REFERENCES

For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

Q224181 BUG: GDI Resource Leak Using Checkboxes in ListView Control

Additional query words:

Keywords : kbCmnCtrls kbCtrl kbTreeView kbVBp kbVBp600bug kbGrpVB
Version : WINDOWS:6.0
Platform : WINDOWS
Issue type : kbbug