Option Explicit
 
Private Declare Function SetWindowLong Lib "user32" _
    Alias "SetWindowLongA" _
    (ByVal hwnd As Long, _
    ByVal nIndex As Long, _
    ByVal dwNewLong As Long) _
    As Long
 
Private Declare Function GetWindowLong Lib "user32" _
    Alias "GetWindowLongA" _
    (ByVal hwnd As Long, _
    ByVal nIndex As Long) _
    As Long
 
Private Declare Function GetSystemMenu Lib "user32" _
    (ByVal hwnd As Long, _
    ByVal bRevert As Long) _
    As Long
 
Public Declare Function RemoveMenu Lib "user32" _
    (ByVal hMenu As Long, _
    ByVal nPosition As Long, _
    ByVal wFlags As Long) _
    As Long
 
Private Const WS_THICKFRAME = &H40000
Private Const GWL_EXSTYLE = (-20)
Private Const GWL_STYLE = (-16)
 
Public Const MF_BYCOMMAND = &H0&
Public Const SC_CLOSE = &HF060
Public Const SC_MAXIMIZE = &HF030
Public Const SC_MINIMIZE = &HF020
Public Sub MDI()
    Dim MDIStyle As Long
    Dim MDI_Fest_Style As Long
    Dim Tele_Min As Long
    Dim Tele_Max As Long
 
    'MDI-Form extend Style
    Tele_Min = GetWindowLong(MDIForm1.hwnd, GWL_EXSTYLE)
    SetWindowLong MDIForm1.hwnd, GWL_EXSTYLE, Tele_Min Or &H80
 
    'Manuelle Größenänderung (Maus) deaktiviert
    MDIStyle = GetWindowLong(MDIForm1.hwnd, GWL_STYLE)
    MDI_Fest_Style = SetWindowLong(MDIForm1.hwnd, GWL_STYLE, _
    MDIStyle And Not (WS_THICKFRAME))
 
 
End Sub