在两个不同的程序实例中发送消息，相互通信

有时候，我们需要让不同的应用程序实例间相互发送消息，比如，为了确保对于同一个应用程序，只运行一个的实例，在启动程序时，先检测是否已有此程序的实例运行，如果有，则给此实例发送消息，通知它激活并保持最前，已提醒用户此程序已经在运行。

利用Win32 API RegisterWindowMessage()可以实现这一功能。

1.要点

• 用Win32 API RegisterWindowMessage()注册生成一个消息，此消息在整个Session中保持唯一，因此可用于同一个Session中不同的应用程序实例相互通信；
• 用PostMessage或SendMessage广播此消息；
• 需要接收处理此消息的程序实例，使用ON_REGISTERED_MESSAGE()宏接收处理此广播消息；

2.实现代码

  1: //Define a unique const string to create the broadcast message
  2: //We can use the GuidGen tool to make sure this string is a unique one
  3: const static LPCTSTR g_AciveMsgName = _T("DBCAAC01-2744-43EE-9FFC-7CD41C672842");
  4: 
  5: //Generate a broadcast message
  6: UINT broadcastMsg = ::RegisterWindowMessage(g_AciveMsgName);
  7: 
  8: //Broadcast message
  9: ::PostMessage(HWND_BROADCAST,broadcastMsg,0,0);
 10: 
 11: //Receive and process this message,if the receiver is a different app instance,it need
 12: //also to call the ::RegisterWindowMessage(g_AciveMsgName) API to get the message code
 13: //NOTE:This message code is assotiated with the global unique string(g_AciveMsgName)
 14: //and it's allocated by the windows system
 15: BEGIN_MESSAGE_MAP(...)
 16: 	//......
 17: 	ON_REGISTERED_MESSAGE(s_WM_ACTIVEWND,OnActiveWnd)
 18: 	//......
 19: END_MESSAGE_MAP()
 20: 
 21: void CDlg::OnActiveWnd()
 22: {
 23: 	// Do something to response this broadcasted message
 24:         //......
 25: }