Чекбоксы в ListView - VB

Option Explicit
 
Private Enum ChkState
    CS_UNCHECKED = 1
    CS_CHECKED = 2
    CS_GRAYED = 3
End Enum
Private Sub Form_Load()
    tvwTree.Nodes.Add , , "main1", "Main 1", CS_UNCHECKED
    tvwTree.Nodes.Add , , "main2", "Main 2", CS_UNCHECKED
    tvwTree.Nodes.Add , , "main3", "Main 3", CS_UNCHECKED
    tvwTree.Nodes.Add "main1", tvwChild, "main1ch1", "Child1", CS_UNCHECKED
    tvwTree.Nodes.Add "main1", tvwChild, "main1ch2", "Child2", CS_UNCHECKED
    tvwTree.Nodes.Add "main1", tvwChild, "main1ch3", "Child3", CS_UNCHECKED
    tvwTree.Nodes.Add "main1ch1", tvwChild, "main1ch1ch1", "Child1", CS_UNCHECKED
    tvwTree.Nodes.Add "main1ch1", tvwChild, "main1ch2ch1", "Child2", CS_UNCHECKED
    tvwTree.Nodes.Add "main1ch1ch1", tvwChild, "main1ch1ch1ch1", "Child1", CS_UNCHECKED
    tvwTree.Nodes.Add "main1ch1ch1", tvwChild, "main1ch2ch1ch1", "Child2", CS_UNCHECKED
    tvwTree.Nodes.Add "main1ch2ch1ch1", tvwChild, "main1ch1ch1ch1ch1", "Child1", CS_UNCHECKED
    tvwTree.Nodes.Add "main1ch2ch1ch1", tvwChild, "main1ch2ch1ch1ch1", "Child2", CS_UNCHECKED
    tvwTree.Nodes.Add "main2", tvwChild, "main2ch2", "Child2", CS_UNCHECKED
    tvwTree.Nodes.Add "main2", tvwChild, "main2ch3", "Child3", CS_UNCHECKED
End Sub
 
Private Sub tvwTree_MouseDown(Button As Integer, Shift As Integer, X As Single, y As Single)
    Dim Sel As Node, Pt As Node
    Dim Lvl As Long
    Dim nX As Long, dx As Long
    
    Set Sel = tvwTree.HitTest(X, y)
    
    If Sel Is Nothing Then Exit Sub
    
    Set Pt = Sel
    
    X = ScaleX(X, vbTwips, vbPixels) - 3
    
    Do Until Pt.Parent Is Nothing
        Set Pt = Pt.Parent
        Lvl = Lvl + 1
    Loop
    
    nX = Lvl * tvwTree.Indentation
    dx = X - nX
    
    If dx <= iglIcon.ImageWidth Then
        If Sel.Image = CS_UNCHECKED Or Sel.Image = CS_GRAYED Then
            Sel.Image = CS_CHECKED
            MarkAllChild Sel, CS_CHECKED
        Else
            Sel.Image = CS_UNCHECKED
            MarkAllChild Sel, CS_UNCHECKED
        End If
        
        MarkAllParents Sel
 
    End If
End Sub
Private Sub MarkAllParents(Child As Node)
    Dim Prnt As Node
    Dim Chld As Node
    Dim Ct As Long
    Dim IsGr As Boolean
    
    Set Prnt = Child.Parent
    
    If Not Prnt Is Nothing Then
        Set Chld = Child.FirstSibling
        Do Until Chld Is Nothing
            If Chld.Image = CS_CHECKED Then
                Ct = Ct + 1
            ElseIf Chld.Image = CS_GRAYED Then
                Ct = Ct + 1
                IsGr = True
                Exit Do
            End If
            Set Chld = Chld.Next
        Loop
        If Ct = 0 Then
            Prnt.Image = CS_UNCHECKED
        ElseIf IsGr Or Ct < Prnt.Children Then
            Prnt.Image = CS_GRAYED
        ElseIf Ct = Prnt.Children Then
            Prnt.Image = CS_CHECKED
        End If
        
        MarkAllParents Prnt
    End If
End Sub
Private Sub MarkAllChild(Parent As Node, Value As ChkState)
    Dim Chld As Node
    
    Set Chld = Parent.Child
    Do Until Chld Is Nothing
        Chld.Image = Value
        If Chld.Children Then MarkAllChild Chld, Value
        Set Chld = Chld.Next
        DoEvents
    Loop
End Sub