Posting user defined message - MFC

pYourWnd->PostMessage( WM_SAVEIMAGES, 123, 456 );

LRESULT CYourWnd::OnSaveImages( WPARAM wParam, LPARAM lParam )
{
ASSERT( wParam == 123 );
ASSERT( lParam == 456 );

return 0;
}

ASKER

Unfortunatelly I can not managed to save the image...
I have a function called Calculate():
void CBitmap::Calculate(Image Img)
{ .....
// do something
...
//display the image
PostMessage(WM_DISPLAYIMAGE, 0, 0);
//save the image
PostMessage(WM_SAVEIMAGES, 0, 0);
//and then I should do some calculating with the image
...
}
In Calculate(Image Img) before saving the image with PostMessage(WM_SAVEIMAGES,0,0) I displayed it and after saving it I proceed some calculations with the image.This process should occur many times...

Before adding the saving message every thing was fine and but now my application just crashes...

SOLUTION

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>>>> PostMessage(WM_SAVEIMAGES, 0, 0);

PostMessage puts the message at end of message queue. Hence, the saving would occur some time *after* CBitmap::Calculate(Image Img) returned.

You could call SendMessage instead of PostMessage to have the message processed immediately. But, you should pass a handle or pointer with the message and not use shared or global data.

ASKER

>>you should pass a handle or pointer with the message and not use shared or global data
why do you mean by: not use shared or global data?
As handle to passed with the message should I use hWnd=GetSafeHwnd(); or is that unnecessary?
SendMessage will still be called with 3 parameters because it is used within a function of a class derived from CWnd right?

The first parameter is the message code and, of course, it is mandatory.
The second and the third are optional parameters and they depends by the message; in the case of user defined message you can decide to use one, both or none of them.

ASKER CERTIFIED SOLUTION

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>>>> As handle to passed with the message should I use hWnd=GetSafeHwnd();
You also could use CWnd::PostMessage as in most samples above. The CWnd::PostMessage makes the call GetSafeHwnd() before it calls the ::PostMessage(hwnd, ...) from WINAPI.

>>>> SendMessage will still be called with 3 parameters because it is used within a function of a class derived from CWnd right?

Yes, the same applies for PostMessage. But SendMessage is dangerous cause it could deadlock. Better always use PostMessage if you don't need immediately return.

ASKER

>>Better always use PostMessage if you don't need immediately return.
After saving the image I have to perform some calculations with the image.Hence it's maybe better to use SendMessage.
There's something strange. ..I'm calling SendMessage many times in the void CBitmap::Calculate(Image Img) (see above). For example to refresh the image I will be using SendMessage(WM_DISPLAYIMAGE, 0, 0);and since I don't write afterwards the following satements:

if (::PeekMessage(&message, NULL, 0, 0, PM_REMOVE)) {
            ::TranslateMessage(&message);
            ::DispatchMessage(&message);
      }
my image won't be refreshed at all... Is that normal ???

ASKER

I wanted to say it doesn't matter if I use SendMessage(WM_DISPLAYIMAGE, 0, 0) or PostMessage(WM_DISPLAYIMAGE, 0, 0) I will still have to add the statements above...