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Losing access to my dialog box in MFC

matth012098 asked
Last Modified: 2013-12-03
I have recently been implementing an app to download some files from the internet and stumbled across the following problem:-

I bring up a dialog box using DoModal(), and in that dialog box I have a button called start. I have a handler called OnStartButtonPressed() which is called when ever I press the start button. The code within this button handler downloads a bunch of files from the internet, however I seem to not be able to interact with it once it starts downloading the files. I can no longer do any of the following:-

a) Adjust the dialogs position or size etc...
b) interact with any of the buttons or text boxes within the dialog box
c) Cancel and OK do not even respond.
d) I cant even close the dialog box.

The only way I can stop it before it has finished downloading the files is to use CTRL+ALT+DEL and shuit it down even then it hangs around in the system for a bit.

I have a CProgressCtrl in the dialog which is the only that that works.

I can get to other applications and use them fine, it seems like I have locked my dialog window up whilst the handler downloads the internet files.

How do I get around this, is it possible without using threads?


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Tommy HuiEngineer

Instead of using a modal dialog, you can create a modeless dialog box. The problem is your function that downloads files is not processing any messages. You can use


to process messages in your loop.


PumpMessage() is a CSocket method, unfortunately I cannot use this since I am using WinINet CInternetSession (sorry, I should have mentioned this). I created a modeless dialog box as follows:-

I created a dialog box and class from it using ClassWizard
I have overriden the Create function as follows:-

CWebGet::Create(UINT nID, CWnd *pWnd)
  return CDialog::Create(nID, pWnd);
I also overriden OnOK(), OnCancel() and CWnd::PostNcDestroy() in the dialog class as follows:-

void CWebGet::OnCancel()
void CWebGet::OnOK()
    if (!UpdateData(TRUE))
virtual void CWebGet::PostNcDestroy() {delete this;}

I then create the dialog box like this:-

CWebGet *dlg = new CWebGet;
dlg.Create(IDD_DIALOG_WEB, this);

The dialog box is displayed and I can interact with it, but as soon as I click the START button and the handler starts downloading internet files, I am locked out of the dialog box again, I have still the same probs.



Also, the dialog box is not getting redrawn whilst downloading. If I switch to a dos prompt and alt-TAB back to my application the window is white with borders. I guess this is something to do with the dialog box not processing the redraw message. I understand that creating a modeless dialog is ran as a seperate thread to the window that created it, and when I press START on the dialog, it gets trapped in my loop downloading files from the net, so the dialog window will not process messages. Is there a specific command to force the dialog to handle any messages within the internet download loop?


I have found half the solution to this question and that is to use the win32 functions GetMessage(), TranslateMessage() and DispatchMessage(). I wrote the following function to take care of it

BOOL ProcessMessages(HWND hWnd, int loop)
  MSG msg;
  int t;
  BOOL ret = TRUE;

  for (t=0; t<loop; t++)
    ret=GetMessage(&msg, hWnd, 0, 0);
    if (!ret)
  return ret;

This will process a number of messages for the required window which is in my case the dialog box defined by CWebGet.

This works but it maybe 2 seconds or so before the message is acknowledged, if anyone knows of a better way especially in MFC of doing this that I can easily implement I will award them the points


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