I want to print a text on MFC Dialog - mfc

Question

I made a thread to set some text on EditBox on Lobby Dialog. Below is my code.
And MainLobby is the Dialog Class. This project is "Dialog Based MFC Project".
MainLobby Lobby;
_beginthreadex(NULL, 0, ReceiveMessage, (void *)Lobby.GetSafeHwnd(), 0, NULL);
Lobby.DoModal();
But it doesn't work. Where is wrong? I thought hard but I couldn't find the answer.
I tried not Lobby.GetSafeHwnd() but Lobby.m_hwnd
unsigned WINAPI ReceiveMessage(void *arg)
{
HWND hDlg = (HWND)arg;
char msg[BUF_SIZE];
int msgLen;
while( (msgLen = recv(CClientApp::hSocket, msg, BUF_SIZE, 0)) != 0 )
{
SetDlgItemText(hDlg, IDC_LOBBY_CBOX, msg);
}
}
I am using MFC now. I will be glad a good idea.

Answer 1

The device context has to be updated.
Try:
UpdateData(true);
SetDlgItemText(hDlg, IDC_LOBBY_CBOX, msg);
UpdateData(false);
Or try it with a CString member variable for IDC LOBBY CBOX.

Answer 2

It is clear from your code that you are not using MFC properly. A Windows dialog based application does not require the programmer to explicitly create message handlers or receivers, that is what the MFC framework itself is doing for you. There is no reason to call beginthreadex before starting the dialog message loop as part of the DoModal method. When you invoke DoModal on any class descended From Dialog or DialogEX, the window is constructed, the member objects are constructed, and the message loop is started before the WM_INITDIALOG message is sent to the dialog for any other initialization before the dialog window is displayed. Once the window is displayed, the message loop is running, and text will display automatically in an edit control when you send it correctly. Normally one would declare a CEdit object with some name using the Class Wizard in visual studio then map the MFC object to the dialog object. Rather than type out all the details I will refer to this article: http://msdn.microsoft.com/en-us/library/6d1asasd.aspx

Answer 3

The dialog's HWND has not been initialized before DoModal is called. So your thread does not receive the proper HWND. The first place that you can access the correct HWND value is inside the dialog's OnInitDialog member function.

Answer 4

I see two problems in your code.
First you are calling Lobby.GetSafeHwnd before DoModal, so before the window is constructed. You should move the thread creation to the WM_INITDIALOG handler of MainLobby to create the thread there. Or you could create a modeless dialog.
Second you are using _beginthreadex in your MFC code. If you are starting a thread that uses MFC, then you need to start that thread with AfxBeginThread. If you only use CRT, then you use _beginthreadex. If you use neither, then use Windows CreateThread. The reason for this is that each layer (CRT, MFC) needs to do some housekeeping of thread specific information. This can only be done if you call the proper thread creation functions.
Third, you might consider using the MFC socket objects like CAsyncSocket. This object can send windows messages to your dialog if some data is available on the socket. This perfectly fits into your scenario with an MFC dialog that should handle socket data.
Another thing, but you already got that right: to access an MFC GUI object you need to be in the thread of that GUI object. So calling the Windows SetDlgItemText with the raw handle hDlg needs to be done, you cannot call an MFC function here.
BTW, are you sure your overall strategy is right? I don't see how you handle dialog life time, socket life time and how you put both together.