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Editorial Team
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Asked: 2026-06-17T17:30:14+00:00

I have a COleControl object in my project. Inside this COleControl, I have a

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I have a COleControl object in my project.
Inside this COleControl, I have a CRectTracker object.

I want to handle the windows message (event) of WM_LButtonUp. (when the user stops to press the left mouse button).

In my .h file I wrote:

afx_msg void OnLButtonUp(UINT nFlags, CPoint point);

In my .cpp file, in

BEGIN_MESSAGE_MAP(CMyControl, COleControl)

I added

ON_WM_LBUTTONUP()

Then I developed a method of

void CMyControl::OnLButtonUp(UINT nFlags, CPoint point)

I did the same thing for the windows message LButtonDown.

When I leave the left mouse button inside my control, method get handles and everything works fine.
The problem occurs when I leave the left mouse button when the mouse tracker is on the CRectTracker object. In this case, the mouse LButtonUp message does not get handled.

I tried to use Spy++ and I can see that the windows message WM_LButtonUp exists and occurs as expected. But it my code, it does not get handled (just in the case of mouse on the CRectTracker).

The LButtonDown event get handled successfully all the time, even when I press the mouse button while the mouse is on the CRectTracker.

What can be the problem with the LButtonUp message?

Thanks

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1 Answer

  1. Editorial Team

    That is just an inevitable side-effect of the way the tracker works. Once you click on the tracker or one of the sizing handles then MFC captures the mouse and starts a modal message loop. Which is going to pick off mouse-move and button-up messages to implement the tracking operation. That loop doesn’t exit until the left button-up message is seen, the Escape key is seen or the capture is lost. Accordingly, your OnLButtonUp() function cannot run while that loop is active, the message was intercepted before it could be dispatched.

    You’ll need to do this differently, not relying on OnLButtonUp(). Hard to give specific advice since you didn’t describe why you need it. The source code for the modal loop is in atlmfc/src/mfc/trckrect.cpp, CRectTracker::TrackHandle() if you need more insight.

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