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Display Update Speed for Dialog Boxes

Friday Jan 14th 2000 by Joseph C. Burwell

Display Update Speed for Dialog Boxes

Environment: Visual C++ 6

I've been searching for a simple answer to a problem. I wanted to increase the display update rate for a dialog box. This (modeless) dialog includes a progress bar, and it displays a percentage number and another number indicating progress (initially in edit boxes). When I'd disable the display update functions (m_progress.SetPos() and dlg->UpdateData(FALSE), the function generating these numbers would complete in half the time. I tried using a DC and the TextOut() function (rather than updating the edit boxes), but that didn't speed things up either. Until I looked at the myriad of windows messages sent when I used UpdateData(FALSE) I didn't realize the origin of the wasted time. It's all due to the "repainting" of the main app window (frame). Since I'm (relatively) inexperienced with MFC, I'm delighted to find such a simple solution. When you display the dialog box hide the main window (if you don't require it's use at that time). I don't use the UpdateData(FALSE) function, but I still see the information on the screen, and the progress bar updates as expected (in a negligible amount of time). I'm sure some of you may see holes in my theory, but this works fine for my app.



BOOL CMyDialog::OnInitDialog()
{
 CDialog::OnInitDialog();

 CWnd* temp_main_wnd = AfxGetMainWnd();

 temp_main_wnd->ShowWindow(SW_HIDE);
}


void CMyOperation::GetDataAndDisplay()
{
 unsigned int  m_percent = 0;
 unsigned int  m_other_data = 0;

 int x = 200;
 int y = 200;

 CMyDialog* dlg;

 CDC* TempDC = NULL;
 CDC  LocalDC;

 dlg = new CMyDialog;
 dlg->Create(IDD_MY_DIALOG, NULL);
 dlg->ShowWindow(SW_SHOWNORMAL);

 TempDC = dlg->GetDC();

 LocalDC.m_hAttribDC = TempDC->m_hAttribDC;
 LocalDC.m_hDC = TempDC->m_hDC;

 ...
 ...

 // When it's time to update the display...

 dlg->m_progress.SetPos(m_percent);

 LocalDC.TextOut(x, y, m_percent);
 LocalDC.TextOut(x, y + 50, m_other_data);

 ...
 ...
}

void CMyDialog::OnCancel()
{
 CWnd* temp_main_wnd = AfxGetMainWnd();

 temp_main_wnd->ShowWindow(SW_SHOW);

 CDialog::OnCancel();
}	
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