CClientDC dc(this) -- does this fail if window is open?

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Hello everyone.

I have implemented a custom tooltip below is the code. Below is the function taht is called at last while drawing the tip.

CClientDC dc(this);
DrawTip(&dc);

void CustomToolTipPlain::DrawTip(CDC *pDC)
{
	if (pDC)
	{
		BITMAP	bm;
		m_tipImage->GetBitmap(&bm);
		CDC		dcMem;
		dcMem.CreateCompatibleDC(pDC);
		CBitmap *oldBitmap = dcMem.SelectObject(m_tipImage);
		pDC->BitBlt(0, 0, bm.bmWidth, bm.bmHeight, &dcMem, 0, 0, SRCCOPY);
		dcMem.SelectObject(oldBitmap);
	}
}

There is also another function

void CustomToolTip::OnTimer(UINT)
{
    if (!MouseInTipArea())
    {
        HideTip();
    }
    else
    {
        ShowWindow(SW_SHOW);
    }
}

Now in the situation where the Ontimer function is called before even calling the CClientDC dc(this); and finishing the drawing (DrawTip(&dc);
)

My tooltip is always blank in this situation and it doesn't draw anything. It just shows a blank window from the ShowWindow(SW_SHOW) function of the OnTimer.

From the debugging its clear that the call to CClientDC dc(this); is giving a blank dc value when the window is open. Is this true,do you guys think this is the reason? So my question is:

Does CClientDC dc(this); fails when the client windows is open?

Posted 21-Apr-11 6:44am

amarasat

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Richard MacCutchan · Accepted Answer · 2011-04-21T08:00:00

Solution 1

From what you have posted above it looks like you are calling CClientDC dc(this); from outside of any class or function where this would have a valid value.

Posted 21-Apr-11 8:00am

Richard MacCutchan

Comments

amarasat 21-Apr-11 14:24pm

But it is working always, only in this case its not working. This code is grabbed from

http://www.codeproject.com/KB/miscctrl/CustomToolTips.aspx.

The only thing i changed is adding the OnTimer function i gave above

Richard MacCutchan 21-Apr-11 15:20pm

Take a look here: http://msdn.microsoft.com/en-us/library/bb760250%28VS.85%29.aspx

amarasat 26-Apr-11 10:13am

Thanks a lot the answer was solved, my bitmap is having bad dimensions

Hans Dietrich · Accepted Answer · 2011-04-21T08:30:00

Solution 2

Usually a function like DrawTip() would be called from the OnPaint() handler. Where are you calling this function?

In any case, to answer your question, yes, it's ok to use CClientDC when the window is open. Have you checked the bitmap? Did you verify it was loaded? Did you check the bitmap dimensions?

Posted 21-Apr-11 8:30am

Hans Dietrich

Updated 21-Apr-11 8:31am

v2

Comments

amarasat 26-Apr-11 10:13am

Thanks, The bitmap is having bad dimensions.