Advanced MFC Programming

Chapter 13. Adding Special Features to Application
Function CMainFrame::OnSendStr(…) is listed as follows, it demonstrates how message
MSG_SENDSTRING is handled in “MsgRcv”. Like a normal WM_MESSAGE type message handler, this function
has two parameters that are used to pass WPARAM and LPARAM. In the sample, WPARAM parameter is used to
pass the window handle of “Sender”, from which we can obtain a CWnd type pointer and use it to send
MSG_RECEIVED message back. After that the value obtained from LPARAM parameter is added to the list view.
The following is this function:
LONG CMainFrame::OnSendStr(UINT wParam, LONG lParam)
{
CWnd *pWnd;
CString szText;
pWnd=CWnd::FromHandle((HWND)wParam);
ASSERT(pWnd != NULL);
szText.Format("%d", (int)lParam);
pWnd->PostMessage(g_uMsgReceived);
CListCtrl &lc=((CMsgRcvView *)GetActiveView())->GetListCtrl();
lc.InsertItem(lc.GetItemCount(), szText);
}
return (LONG)TRUE;
On the “Sender” side, if the user presses “Send” button, we call function CWnd::FindWindow(…) to find
the mainframe window of “MsgRcv”. If it exists, message MSG_SENDSTRING will be sent to it, with the
WPARAM parameter set to the window handle of the dialog box and LPARAM parameter set to the number
contained in the edit box:
void CSenderDlg::OnButtonSend()
{
CWnd *pWnd;
}
UpdateData(TRUE);
pWnd=CWnd::FindWindow(CLASS_NAME_RECIEVER, NULL);
if(pWnd != NULL && ::IsWindow(pWnd->m_hWnd))
{
pWnd->PostMessage(g_uMsgSendStr, (WPARAM)GetSafeHwnd(), (LPARAM)m_nSent);
}
Message MSG_RECEIVED is mapped to function CSenderDlg::OnReceive(…). Upon receiving message
MSG_RECEIVED, we simply increment the counter and display the new value in the dialog box:
LONG CSenderDlg::OnReceive(UINT wParam, LONG lParam)
{
m_nCount++;
UpdateData(FALSE);
}
return (LONG)TRUE;
It is fun to play with the two applications, because they implement the simplest communication
protocol: sending the message, replying with the acknowledgment. By using message communication, we
can send only simple information (like integers) to another application. If we want to send complex data
structure to other processes, we need to use other memory sharing techniques such as file mapping along
with message sending.
13.9 Z-Order
Z-order represents the third dimension of a window besides its x and y position. Under Windows, a
window can be placed before or after another window, and none of the two windows can have a same Z-
order (This means if the two windows share a common area, one of them must be overlapped by the other).
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