利用子类处理技术限制窗体的大小

' * * * * * * * * * * 警告 * * * * * * * * * * * * *
' 对以下代码进行修改将有可能导致不可预料的后果,甚至能使您的VB崩溃!
' 在VB IDE环境中运行本程序之前请先保存您的修改
' 不要使用断点调试模式,这将导致VB崩溃!
' * * * * * * * * * * 注意 * * * * * * * * * * * * *
模块:
Option Explicit

Public OldWindowProc As Long
Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long) As Long
'从指定的窗口结构中取得信息
'参数/类型 说明
'hwnd(long): 欲为其获取信息的窗口的句柄
'nIndex(long): 欲取回的信息,可以是下述任何一个常数
'GWL_EXSTYLE:扩展窗口样式
'GWL_STYLE:窗口样式
'GWL_WNDPROC:该窗口的窗口函数的地址
'GWL_HINSTANCE:拥有窗口的实例的句柄
'GWL_HWNDPARENT:该窗口之父的句柄.不要用 SetWindowWord 来改变这个值
'GWL_ID:对话框中一个子窗口的标识符
'GWL_USERDATA:含义由应用程序规定
'对话框亦可指定下列常数
'DWL_DLGPROC:这个窗口的对话框函数地址
'DWL_MSGRESULT:在对话框函数中处理的一条消息返回的值
'DWL_USER:含义由应用程序规定
Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
'在窗体结构中为指定的窗口设置信息
'参数/类型 说明
'hwnd(long) 欲为其获取信息的窗口的句柄
'nIndex(long) 参考GetWindowLong函数
'dwNewLong(long) 由nIndex指定的窗口信息的新值
Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (pDest As Any, pSource As Any, ByVal ByteLen As Long)
'这就是在VisualBasic中处理指针的"短柄斧"--CopyMemory.你可能在API文档中找不到它,但它确实存在,并且功能异常强大
'参数/类型 说明
'pDest 你想写入字节到其中的任何变量的ByRef参数(地址)
'pSource 要从其中进行复制的ByRef变量
'ByteLen 要复制的字节数
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
'把控制权传回给原来的窗口过程
Public Const WM_GETMINMAXINFO = &H24
Type POINTAPI
　 x As Long
　 y As Long
End Type
' This is the structure that is passed by reference(ByRef)(ie an address) to your message handler(消息侦听器)
' The key items in this structure are ptMinTrackSize and ptMaxTrackSize
Type MINMAXINFO
　 ptReserved As POINTAPI
　 ptMaxSize As POINTAPI
　 ptMaxPosition As POINTAPI
　 ptMinTrackSize As POINTAPI
　 ptMaxTrackSize As POINTAPI
End Type
Public Function SubClass1_WndMessage(ByVal hwnd As Long, ByVal Msg As Long, ByVal wp As Long, ByVal lp As Long) As Long
' Watch for the pertinent message to come in
　 If Msg = WM_GETMINMAXINFO Then
　　 Dim MinMax As MINMAXINFO
' 　This is necessary because the structure was passed by its address and there
' 　is currently no intrinsic way to use an address in Visual Basic
　　 CopyMemory MinMax, ByVal lp, Len(MinMax)
' This is where you set the values of the MinX,MinY,MaxX, and MaxY
' The values placed in the structure must be in pixels. The values
' normally used in Visual Basic are in twips. The conversion is as follows:
' 　pixels = twips\twipspERPixel
　　 MinMax.ptMinTrackSize.x = 3975 \ Screen.TwipsPerPixelX
　　 MinMax.ptMinTrackSize.y = 1740 \ Screen.TwipsPerPixelY
　　 MinMax.ptMaxTrackSize.x = Screen.Width \ Screen.TwipsPerPixelX \ 2
　　 MinMax.ptMaxTrackSize.y = 3480 \ Screen.TwipsPerPixelY
' Here we copy the datastructure back up to the address passed in the parameters
' because Windows will look there for the information.
　　 CopyMemory ByVal lp, MinMax, Len(MinMax)
' This message tells Windows that the message was handled successfully
　　 SubClass1_WndMessage = 1
　　 Exit Function
　 End If
' Here, we forward all irrelevant messages on to the default message handler.
　 SubClass1_WndMessage = CallWindowProc(OldWindowProc, hwnd, Msg, wp, lp)
End Function

窗体代码:
Option Explicit

Private Const GWL_WNDPROC = (-4)
Private Sub Form_Load()
' First, we need to store the address of the existing Message Handler
　 OldWindowProc = GetWindowLong(Me.hwnd, GWL_WNDPROC)
' Now we can tell windows to forward all messages to out own Message Handler
　 Call SetWindowLong(Me.hwnd, GWL_WNDPROC, AddressOf SubClass1_WndMessage)
End Sub

Private Sub Form_Unload(Cancel As Integer)
' We must return control of the messages back to windows before the program exits
Call SetWindowLong(Me.hwnd, GWL_WNDPROC, OldWindowProc)
End Sub

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