C / C++ / MFC

11-Jun-04 5:39

Here how I want to apply.
When the user clicked on run button, application call the function, f1, that does something like reading array and changing something one index by a time. When the job of array index is done, it post the message to go to next job. Another function, f2, was waiting for the message to do its job. As soon as f2 gets the message from f1, it starts its job.
Meanwhile, the user clicked on Stop then immediately the application stop whatever he doing. the the thread coming from.

Hornestly, I have an idea of it.. but not clear and don't really know how to do it.

How to send messages within an application?
Should I use wm_app or wm_user? What if an application has thread in it?
Should I use postmessage() to send message and getmessage to read the message?

Thank you

David Crow11-Jun-04 6:31

11-Jun-04 6:31

Anonymous wrote:
How to send messages within an application?

By using the SendMessage() function.

Anonymous wrote:
Should I use wm_app or wm_user?

Of the two, WM_APP is preferred. However, a unique registered message is even better.

Anonymous wrote:
Should I use postmessage() to send message and getmessage to read the message?

It depends on if you want the message to reside in the application's queue or not. SendMessage() sends a message to another window immediately by calling that window's procedure and waiting for it to return, whereas PostMessage() queues the message and returns immediately. With SendMessage(), the receiving app processes the message immediately, rather than at some later time, by fetching it from its queue. With PostMessage(), the thread or application processes the message when it gets around to it. That is, when its main dispatch loop calls GetMessage().

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Anonymous11-Jun-04 7:20

11-Jun-04 7:20

Thannk you David for answering my question in detail.
I'm new in sending message and reading it.
I only have one dlg ( window). I think I should give you more detail about my program.

My program is dialog based program, which has 3 buttons, print, stop, and exit on it.
When user clicked on print, the thread gets created. the thread is keeping checking whether the global boolean variable stopPrinting = true. ( stopPrinting is set to TRUE when the user clicked on Stop button)

<br />
UINT PrintingThreadFunction(LPVOID lParam)<br />
{<br />
myApp *dlg = (myApp*)lParam;<br />
while(!stopPrinting) <br />
{<br />
dlg->printafile();<br />
}<br />
}<br />

the file sent to the printer and printer send the message "END_DOC" to application back. To catch the message sent from printer, I used RegisterWindowMessage() first and add the following code to messgae map

BEGIN_MESSAGE_MAP(CSMPClientDlg, CDialog)<br />
	ON_WM_SYSCOMMAND()<br />
	ON_WM_PAINT()<br />
	ON_WM_QUERYDRAGICON()<br />
	//}}AFX_MSG_MAP		<br />
	ON_BN_CLICKED(IDC_PRINT, OnBnClickedPrint)<br />
	ON_BN_CLICKED(IDCANCEL, OnBnClickedCancel)<br />
	ON_BN_CLICKED(IDC_STOP_PRINT, OnBnClickedStopPrint)<br />
<font color = green>	ON_REGISTERED_MESSAGE(BlackIcePrintMessage,OnPrinterMsg)</font><br />
END_MESSAGE_MAP()

I want my applicaton to just listen to or waiting for the message from printer to comes and do nothing. Then when the application got the message END_DOC, send the message, PRINT_NEXT_FILE or wake application up so it can move on next one. At the same time, if the user clicked on Stop button, application should drop whatever its doing.

LRESULT myApp::OnPrinterMsg(WPARAM wParam, LPARAM lParam )
{
...
..
if(wParam == END_DOC)
//send the message PRINT_NEXT_FILE
}

thank you

Anonymous11-Jun-04 7:30

11-Jun-04 7:30

This is how I create the thread
void myApp::OnPrint()
{
CWinThread *printingThread;
printingThread = AfxBeginThread(PrintingThreadFunction,this);
}

Anonymous11-Jun-04 7:48

11-Jun-04 7:48

I'm sorry David.
When you say unique registered message is even better means
use RegisterWindowMessage()?

David Crow11-Jun-04 8:00

11-Jun-04 8:00

Anonymous wrote:
When you say unique registered message is even better means
use RegisterWindowMessage()?

That would be the one!

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Anonymous11-Jun-04 8:32

11-Jun-04 8:32

But isn't it for sending messages between applications?
I already used it which is catching Messages from Printer without really knowing it.
How am I going to let my application stop and wait for the message to coming in.. actually application is just talking to itself.

I got confused, let me clearify and see I'm right.
1) create the thread using AfxThreadBegin() when Print button is clicked. So entire GUI is still alive and user can still click on either Stop or Exit button.

2)Print the file, and wait for the message from printer. Now I'm using global bool variables stopPrinting and printNextfile to stop.

<br />
UINT theThread(...)<br />
{<br />
while(!stopPrinting) <br />
{<br />
 if(printNextfile)<br />
 PrintNextFile();<br />
else if(stopPrinting)<br />
break;<br />
 }<br />
}<br />

it is working fine. the program is doing what I want it to do but I dont' really like it coz it takes so much of CPU time. and Dont' really know to improve it

The solution I guess was take out while loop and why dont'I just respond to message. but how to?
Using RegisterWindowMessage and SendMessage() functions will help?

if(END_DOC)
SendMessage(PRINT_NEXT_FILE);

OnPrintNextFile()
{
printNextfile();
}

So how am I going to stop or respond to Stop Button was clicked?

thanks

David Crow11-Jun-04 8:40

11-Jun-04 8:40

Anonymous wrote:
But isn't it for sending messages between applications?

It can also be used within the same application, whether one window is sending a message to itself, or one window is sending a message to another window. As long as you have the target window's handle, it makes no difference that it belongs to another application.

Anonymous wrote:
1) create the thread using AfxThreadBegin() when Print button is clicked. So entire GUI is still alive and user can still click on either Stop or Exit button.

So far, so good.

Anonymous wrote:
2)Print the file, and wait for the message from printer.

How does the printer signal that it is done printing?

BTW, why don't you register? It's much easier to communicate, and it's free!

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Anonymous11-Jun-04 8:57

11-Jun-04 8:57

The printer send message like window message.
here what I did

1) BlackIcePrintMessage = RegisterWindowMessage(szREGISTERMESSAGE);
where szREGISTERMESSAGE = "colorPrinter"

2)
BEGIN_MESSAGE_MAP(myApp, CDialog)
ON_REGISTERED_MESSAGE(BlackIcePrintMessage,OnPrinterMsg)
END_MESSAGE_MAP()

3)
LRESULT CSMPClientDlg::OnPrinterMsg(WPARAM wParam, LPARAM lParam )
{
..
..
}

I was using above methods without really understanding it.. I read about it but still get confused. So how can application send the message to itself using the same 3 steps?
My big question ( the most still confused) is a thread... Am I still use the infinate loop inside the thread function and watch or wait for the message coming in. or how?

David Crow11-Jun-04 9:36

11-Jun-04 9:36

Anonymous wrote:
So how can application send the message to itself using the same 3 steps?

It matters not to SendMessage() and PostMessage() of the origin of the message (i.e., registered or some arbitrary number like WM_APP + 5). Consider:

BEGIN_MESSAGE_MAP(CMyDialog, CDialog)
    ON_REGISTERED_MESSAGE(BlackIcePrintMessage, OnPrinterMsg)
END_MESSAGE_MAP()
 
LRESULT CMyDialog::OnPrinterMsg( WPARAM, LPARAM )
{
    AfxMessageBox("The printer has finished doing whatever it was doing!");
}
 
UINT ThreadProc( LPVOID pParam )
{
    HWND hWnd = *((HWND *) pParam);
 
    // do some stuff here
 
    PostMessage(hWnd, BlackIcePrintMessage, 0, 0);
 
    return 0;
}
 
void CMyDialog::OnPrint()
{
    HWND hWnd = GetSafeHwnd();
 
    // send the thread a handle to our window.  we could also send it the 'this'
    // pointer but it would be overkill for this example
    AfxBeginThread(ThreadProc, &hWnd);
}

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Anonymous14-Jun-04 3:51

Passing cdc across threads

14-Jun-04 3:51

Thank you very much Dave
I think I understand and let me try it.

thank you again for taking time to explain it patiently.

Member 51425211-Jun-04 5:35

Member 514252

11-Jun-04 5:35

Hi pals,
I am facing a difficulty with CDC across threads.

Actually, i spawn a secondary thread to calculate the display coordinates of the strings. So i am calculating the height and width of the strings based on the font selected in the CDC. It works fine with the scroll view but the calculation goes wrong with the PrintPreview. Bcos ,SelectObject(pMyFont) is always returning NULL.
How do i solve this problem.
Help me out friends. Thanks in advance.

Kumari

palbano11-Jun-04 5:41

palbano

11-Jun-04 5:41

MFC objects do not operate well across threads. There are some Knowledge base articles on MSDN that explain why. Basically they use thread local storage to map the resource handle to the C++ object pointer. So in another thread the mapping does not exist.

So always pass the resource HANDLE rather than an MFC C++ class pointer across threads. then if you want to use MFC classes in the thread you can attach the HANDLE to a thread local scope MFC object.

"No matter where you go, there your are." - Buckaroo Banzai

-pete

suiram4011-Jun-04 7:48

suiram40

11-Jun-04 7:48

Pass the HDC.
Make sure the CDC is retreived by GetDC.
Make thet window class has CS_OWNDC. you get it on WM_CREATE.
you can set the GDI objects into this context once and thay persistent
couse to CS_OWNDC.

Anonymous11-Jun-04 23:57

11-Jun-04 23:57

Hi suiram
Thanks for your response.
Yes i am passing hdc to the thread.
I tried with CS_OWNDC, But of no improvement. My problem is with the CDC of PrintPreview. What should i do now.
Please, do help me.

kumari