DrawText() blinking problem

[econy]

I met a weird DrawText() blinking problem. in a loop, interval is 2 seconds, I want to show some messages on a dialog screen. i.e. 0-2 sec, message1; 2-4 sec,message2; 4-6, message3 ... but, now the message shows like: flash message1; 0 sec black screen; flash message2; 2 sec black screen; flash message3; 6 sec. black screen; what I want is : message1; 0-2 sec message2; 2-4 sec message3; 4-6 sec

void CTestDlg::DrawMsg(LPCTSTR iMsgStr)
{
CDC* pDC;
CRect rect;
CString MsgStr;
HDC hDC;
LOGFONT lf;
HFONT FontNew, FontOld;

pDC = GetDC();
hDC = pDC->GetSafeHdc();

memset(&lf, 0, sizeof(LOGFONT));
lf.lfHeight = -14 * GetDeviceCaps(hDC,LOGPIXELSY)/72;
lf.lfWeight = 0;
FontNew = CreateFontIndirect(&lf);
FontOld = (HFONT)SelectObject(hDC,FontNew);

rect.SetRect(CPoint(274,442), CPoint(514,514));
SetBkMode(hDC,TRANSPARENT);

DrawText(hDC,dtcMsgStr,-1,rect,DT_WORDBREAK|DT_LEFT);
InvalidateRect(rect,FALSE);

SelectObject(hDC,FontOld);
DeleteObject(FontNew);
ReleaseDC(pDC);
}

[PJ Arends]

It goes blank because you call InvalidateRect after you call DrawText, switch them around.

Within you lies the power for good - Use it!

[econy]

InvalidateRect(rect,FALSE);
DrawText(hDC,dtcMsgStr,-1,rect,DT_WORDBREAK|DT_LEFT);

I tried the above way, same phenomenon

[Lost User]

You should not be calling InvalidateRect in the same place as you are drawing to the screen. That call is to tell windows that your window needs to be updated, but you are already inside the code where the update is happening. You could simplify this by using one of the standard window controls[^].

[econy]

In fact, I try to use a CEdit first, like:

//dialog template
LTEXT "N/A" IDC_TEST_MSG 88,189,128,24 //in resource file,
//CPP file
CEdit* pEdit1 = GetDlgItem(IDC_TEST_MSG);
CDC* pEdit1DC = pEdit1.GetDC();
pEdit1DC->DrawText()

But, I got same phenomenon.

[Lost User]

If you are using MFC classes then you should override the OnPaint[^] member function of the class.

[econy]

then if I want to implement the display effect, what should I do? I want to show: message1 0-2 sec, message2 2-4 sec, message3 4-6 sec, ... I hope it like (calendar time) static text, or text box control in many demo program. that is: 2014/3/15 12:51; 2014/3/15 12:52; 2014/3/15 12:53; update time smoothly.

[Lost User]

Use something like a progress dialog.

[econy]

No such thing, it is an embedded Win CE platform

[Lost User]

Pity you did not mention that at the beginning.

[econy]

write a test program in a MFC PC program. Now I think I can use a control, like text box to implement my job. but I am still wonder how can I use CRect/DrawText() to implement the same job.