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Howto limit a window's minimum and maximum size

To accomplish that, we used the code from a Knowledge Base article.

Steps to Create a Sample Application:

1. Create a new Standard EXE project.
 
2. Paste the following code into Form1's code module:

         Option Explicit
   
         Private Sub Form_Load()
             'Save handle to the form.
             gHW = Me.hwnd
   
             'Begin subclassing.
             Hook
         End Sub
   
         Private Sub Form_Unload(Cancel As Integer)
             'Stop subclassing.
             Unhook
         End Sub
    

3. Add a standard module to the project.
 
4. Paste the following code into the module:

         Option Explicit
   
         Private Const GWL_WNDPROC = -4
         Private Const WM_GETMINMAXINFO = &H24
   
         Private Type POINTAPI
             x As Long
             y As Long
         End Type
   
         Private Type MINMAXINFO
             ptReserved As POINTAPI
             ptMaxSize As POINTAPI
             ptMaxPosition As POINTAPI
             ptMinTrackSize As POINTAPI
             ptMaxTrackSize As POINTAPI
         End Type
   
         Global lpPrevWndProc As Long
         Global gHW As Long
   
         Private Declare Function DefWindowProc Lib "user32" Alias _
            "DefWindowProcA" (ByVal hwnd As Long, ByVal wMsg As Long, _
             ByVal wParam As Long, ByVal lParam As Long) As Long
         Private 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
         Private Declare Function SetWindowLong Lib "user32" Alias _
            "SetWindowLongA" (ByVal hwnd As Long, _
             ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
         Private Declare Sub CopyMemoryToMinMaxInfo Lib "KERNEL32" Alias _
            "RtlMoveMemory" (hpvDest As MINMAXINFO, ByVal hpvSource As Long, _
             ByVal cbCopy As Long)
         Private Declare Sub CopyMemoryFromMinMaxInfo Lib "KERNEL32" Alias _
            "RtlMoveMemory" (ByVal hpvDest As Long, hpvSource As MINMAXINFO, _
             ByVal cbCopy As Long)
   
         Public Sub Hook()
             'Start subclassing.
             lpPrevWndProc = SetWindowLong(gHW, GWL_WNDPROC, _
                AddressOf WindowProc)
         End Sub
   
         Public Sub Unhook()
             Dim temp As Long
   
             'Cease subclassing.
             temp = SetWindowLong(gHW, GWL_WNDPROC, lpPrevWndProc)
         End Sub
   
         Function WindowProc(ByVal hw As Long, ByVal uMsg As Long, _
            ByVal wParam As Long, ByVal lParam As Long) As Long
             Dim MinMax As MINMAXINFO
   
             'Check for request for min/max window sizes.
             If uMsg = WM_GETMINMAXINFO Then
                 'necesary for the caption of an MDI child (when maximized)
                 '(Thanks to Marvin Chinchilla for this information)
                 WindowProc = CallWindowProc(lpPrevWndProc, hw, uMsg, _
   		wParam, lParam)

                 'Retrieve default MinMax settings
                 CopyMemoryToMinMaxInfo MinMax, lParam, Len(MinMax)
   
                 'Specify new minimum size for window.
                 MinMax.ptMinTrackSize.x = 200
                 MinMax.ptMinTrackSize.y = 200
   
                 'Specify new maximum size for window.
                 MinMax.ptMaxTrackSize.x = 500
                 MinMax.ptMaxTrackSize.y = 500
   
                 'Copy local structure back.
                 CopyMemoryFromMinMaxInfo lParam, MinMax, Len(MinMax)
   
                 WindowProc = DefWindowProc(hw, uMsg, wParam, lParam)
             Else
                 WindowProc = CallWindowProc(lpPrevWndProc, hw, uMsg, _
                    wParam, lParam)
             End If
         End Function
    

5. Save and run the sample application.
 
6. Attempt to resize Form1.
   
   RESULT: The form is not allowed to be sized smaller than 200 by 200 pixels or larger than 500 by 500 pixels.