消息处理函数的转移

//========================================================================
//TITLE:
//    消息处理函数的转移
//AUTHOR:
//    norains
//DATE:
//    Wednesday  03-January-2008
//Environment:
//    VS2005 + SDK-WINCE5.0-MIPSII  
//    EVC + SDK-WINCE5.0-MIPSII 
//========================================================================

    Windows CE有一个很有意思的API函数,通过SetWindowLong函数可以转移原窗口的消息处理函数为自定义的.敏感的朋友估计一看见,就已经明白可以做什么了.呵呵,难道不是么?
   
   
1.函数使用
 
    SetWindowLong的使用及其简单,比如我们将m_hEdWord窗口的消息处理函数置换为CtrlProc:

    SetWindowLong(m_hEdWord,GWL_WNDPROC,(DWORD)CtrlProc);
    就这么简单,现在只要m_hEdWord窗口收到消息,那么就会自动调用预先定义的CtrlProc.
 
    有设置,自然也有获取,不过这次我们是通过GetWindowLong函数:
    m_pPreProcEdWord = (WNDPROC)GetWindowLong(m_hEdWord,GWL_WNDPROC);
   现在m_pPreProcEdWord存储的就是目前m_hEdWord的消息处理函数地址.不过,其实通过SetWindowLong函数也能获取消息函数地址:
    m_pPreProcEdWord = SetWindowLong(m_hEdWord,GWL_WNDPROC,(DWORD)CtrlProc);
    不过这时候获取的却是在设置CtrlProc消息处理函数之前的函数地址.也就是说,这两段代码中m_pPreProcEdWord等价:
    1).
    m_pPreProcEdWord = SetWindowLong(m_hEdWord,GWL_WNDPROC,(DWORD)CtrlProc);
   
    2).
    m_pPreProcEdWord = (WNDPROC)GetWindowLong(m_hEdWord,GWL_WNDPROC);
    SetWindowLong(m_hEdWord,GWL_WNDPROC,(DWORD)CtrlProc);
    如果需要调用m_pPreProcEdWord指向的函数,则需要用上CallWindowProc:
    CallWindowProc(m_pPreProcEdWord,hWnd,wMsg,wParam,lParam);
   
2.接管Windows Control消息
 
    说了一大堆似乎很有哲理的话,现在就让我们来看看有什么实际的作用吧.
   
    估计这个函数用得最多是在Windows Control中.比如,你想在Edit Box输入某个字符时做一些特殊处理,只能通过SetWindowLong来置换内部的处理函数进而调用自己的特殊处理函数.
   
    我们来举一个非常简单的例子,首先创建一个Edit Box控件,如果在该控件中按下键盘的"ESC",则会退出应用程序.为了方便突出问题的重点,我们的CMainWnd窗口继承于CWndBase(关于CWndBase请见:http://blog.youkuaiyun.com/norains/archive/2007/11/10/1878218.aspx)

#pragma once
#include "wndbase.h"

class CMainWnd :
    public CWndBase
{
public:
    CMainWnd(void);
    ~CMainWnd(void);
    BOOL Create(HINSTANCE hInst, HWND hWndParent, const TCHAR *pcszWndClass, const TCHAR *pcszWndName);

protected:   
    static LRESULT CtrlProc(HWND hWnd, UINT wMsg, WPARAM wParam, LPARAM lParam);

private:
    HWND m_hEdWord; //The window is for inputing the word
    WNDPROC m_pPreProcEdWord; //Pointer to the previous window procedure for the input word window.
};

 

#include "stdafx.h"
#include "MainWnd.h"

//---------------------------------------------------------------------------------------
//Default value
#define IDC_EDIT_WORD        101

//////////////////////////////////////////////////////////////////////
// Construction/Destruction
//////////////////////////////////////////////////////////////////////
CMainWnd::CMainWnd(void)
{
}

CMainWnd::~CMainWnd(void)
{
}

//----------------------------------------------------------------------
//Description:
//    Create the window. It's override function
//
//----------------------------------------------------------------------
BOOL CMainWnd::Create(HINSTANCE hInst, HWND hWndParent, const TCHAR *pcszWndClass, const TCHAR *pcszWndName)
{
    if(CWndBase::Create(hInst, hWndParent, pcszWndClass, pcszWndName) == FALSE)
    {
        return FALSE;
    }

    //The edit window for input the word
    m_hEdWord = CreateWindowEx(WS_EX_TOPMOST,
                                TEXT("EDIT"),
                                TEXT(""),
                                ES_LEFT  | WS_TABSTOP | WS_VISIBLE | WS_CHILD | WS_BORDER,
                                GetSystemMetrics(SM_CXSCREEN) / 3,
                                GetSystemMetrics(SM_CYSCREEN) / 3,
                                GetSystemMetrics(SM_CXSCREEN) / 3,
                                GetSystemMetrics(SM_CYSCREEN) / 3,
                                m_hWnd,
                                (HMENU)IDC_EDIT_WORD,
                                m_hInst,
                                NULL);

    //Store the pointer in the window
    SetWindowLong(m_hEdWord, GWL_USERDATA, (DWORD)this);
    //Get the previous window procedure
    m_pPreProcEdWord = (WNDPROC)GetWindowLong(m_hEdWord,GWL_WNDPROC);
    //Set the new window procedure
    SetWindowLong(m_hEdWord,GWL_WNDPROC,(DWORD)CtrlProc);

    return TRUE;
}

//----------------------------------------------------------------------
//Description:
//    Windows control process.
//
//----------------------------------------------------------------------
LRESULT CMainWnd::CtrlProc(HWND hWnd, UINT wMsg, WPARAM wParam, LPARAM lParam)
{
    CMainWnd *pObject = (CMainWnd *)GetWindowLong(hWnd,GWL_USERDATA);

    if(pObject->m_hEdWord == hWnd)
    {
        switch(wMsg)
        {
            case WM_CHAR:
            {
                if((TCHAR) wParam == VK_ESCAPE)
                {
                    PostQuitMessage(0x00);
                }
                break;
            }
        }
        return CallWindowProc(pObject->m_pPreProcEdWord,hWnd,wMsg,wParam,lParam);
    }

   
    //It should never get here !
    return DefWindowProc(hWnd,wMsg,wParam,lParam);
}

    程序代码段很短,但有几点需要注意的地方.
   
    CtrlProc是我们用来置换原有过程的消息处理函数,因为CtrlProc为静态才能回调,而静态函数无法调用成员变量,所以我们在创建Edit Box实例之后在GWL_USERDATA地址存储了当前对象指针:

    SetWindowLong(m_hEdWord, GWL_USERDATA, (DWORD)this);
    然后在CtrlProc函数中获取存储在GWL_USERDATA中的对象指针,用该指针调用成员变量及函数:

    CMainWnd *pObject = (CMainWnd *)GetWindowLong(hWnd,GWL_USERDATA);
    因为我们只是处理WM_CHAR消息,其它消息都采用默认处理方式,所以直接返回调用先前的消息函数:

 return CallWindowProc(pObject->m_pPreProcEdWord,hWnd,wMsg,wParam,lParam);
   这个例子很简单,该工程可以在此下载:http://download.youkuaiyun.com/source/324833

3.系统必崩溃代码

    如果将消息处理函数处理转移到已经释放的内存上,那么会有什么结果呢?结果就是,系统崩溃!有兴趣的朋友可以试试这段代码:

LRESULT MyProc(HWND hWnd, UINT wMsg,WPARAM wParam, LPARAM lParam)
{
    return DefWindowProc(hWnd,wMsg,wParam,lParam);
}

int WINAPI WinMain(    HINSTANCE hInstance,
                    HINSTANCE hPrevInstance,
                    LPTSTR    lpCmdLine,
                    int       nCmdShow)
{
     // TODO: Place code here.

    HWND hWnd = GetForegroundWindow();
    SetWindowLong(hWnd,GWL_WNDPROC,(DWORD)MyProc);
    return 0;
}

本文来自优快云博客，转载请标明出处：http://blog.youkuaiyun.com/norains/archive/2008/01/03/2023986.aspx

转载于:https://www.cnblogs.com/Jade2009/archive/2010/01/19/1651644.html