The TreeView control exposes the AfterLabelEdit event to let the programmer validate the text entered in a Node, but there is no way to trap keys as they are typed by the user. This prevents you from discarding unwanted characters while the user types them.

You can work around this problem by subclassing the Edit control that the TreeView control creates when entering the node edit mode. The following code uses the MSGHOOK.DLL library, that you can download from the FileBank on this site, to discard spaces:

' REQUIRES THE MSGHOOK.DLL LIBRARYPrivate Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal _    hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, _    lParam As Any) As LongPrivate Const TV_FIRST = &H1100Private Const TVM_GETEDITCONTROL = TV_FIRST + 15Dim WithEvents TVHook As MsgHook' start subclassing of the Edit control used when in edit modePrivate Sub TreeView1_BeforeLabelEdit(Cancel As Integer)    Dim editHWnd As Long    ' get the handle of the TreeView's Edit control    editHWnd = SendMessage(TreeView1.hWnd, TVM_GETEDITCONTROL, 0, ByVal 0&)    ' subclass it        TVHook.StartSubclass editHWndEnd SubPrivate Sub TreeView1_AfterLabelEdit(Cancel As Integer, NewString As String)    ' stop subclassing when exiting edit mode    TVHook.StopSubclassEnd SubPrivate Sub Form_Load()    ' create an instance of the subclassing control    Set TVHook = New MsgHookEnd Sub' discard spaces as they are entered by the userPrivate Sub TVHook_BeforeMessage(uMsg As Long, wParam As Long, lParam As Long, _    retValue As Long, Cancel As Boolean)    If uMsg = WM_CHAR Then        ' wParam contains the character code        If wParam = 32 Then Cancel = True    End IfEnd Sub