MDI_FRAMEhWnd = FindWindowEx(frmMdiChild.hwnd, 0, "MDICLIENT", "")

Private Declare Function SetWindowLong Lib "user32.dll" Alias "SetWindowLongA" ( _
     ByVal hwnd As Long, _
     ByVal nIndex As Long, _
     ByVal dwNewLong As Long) As Long
Private Declare Function GetWindowLong Lib "user32.dll" Alias "GetWindowLongA" ( _
     ByVal hwnd As Long, _
     ByVal nIndex As Long) As Long
Private Declare Function FindWindowEx Lib "user32.dll" Alias "FindWindowExA" ( _
     ByVal hWnd1 As Long, _
     ByVal hWnd2 As Long, _
     ByVal lpsz1 As String, _
     ByVal lpsz2 As String) As Long
Private Const MDIS_ALLCHILDSTYLES As Long = &H1
Private Const GWL_STYLE As Long = -16
Private g_OldStyle As Long
Private MDI_FRAMEhWnd As Long
 
Private Sub ZeigeMdiChildForm()
 
    frmMdiChild.Show()
 
    MDI_FRAMEhWnd = FindWindowEx(frmMdiChild.hwnd, 0, "MDICLIENT", "")
 
    g_OldStyle = GetWindowLong(MDI_FRAMEhWnd, GWL_STYLE)
    SetWindowLong MDI_FRAMEhWnd, GWL_STYLE, g_OldStyle Or MDIS_ALLCHILDSTYLES
 
    Set frmMdiChild.RefocusForm = Me
End Sub