I've never worked with the TrueDB Grid control, but I believe you can subclass it by intercepting the WM_NCRBUTTONDOWN message.
VB Code:
Public Declare Function SetWindowLong& Lib "user32" _
Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As _
Long, ByVal dwNewLong As Long)
Public Declare Function CallWindowProc Lib "user32" _
Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, ByVal _
hwnd As Long, ByVal msg As Long, ByVal wParam As Long, ByVal _
lParam As Long) As Long
Const GWL_WNDPROC = (-4)
Const WM_NCRBUTTONDOWN = &HA4
Public WndProcOld As Long
Public Function WindProc(ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
If wMsg = WM_MYMESSAGE Then
MsgBox "Message recieved"
Exit Function
End If
WindProc = CallWindowProc(WndProcOld&, hwnd&, wMsg&, wParam&, lParam&)
End Function
Sub SubClassWnd(hwnd As Long)
WndProcOld& = SetWindowLong(hwnd, GWL_WNDPROC, AddressOf WindProc)
End Sub
Sub UnSubclassWnd(hwnd As Long)
SetWindowLong hwnd, GWL_WNDPROC, WndProcOld&
WndProcOld& = 0
End Sub
'[b][u]Usage[/u][/b]
Private Sub Form_Load()
SubClassWnd hwnd
End Sub
Private Sub Form_Unload(Cancel As Integer)
UnSubclassWnd hwnd
End Sub