MouseLeave and MouseEnter functions

• Download demo project - 96 Kb

Introduction

Whenever MFC applications are written and, above all whenever we write controls, it often happens that we want to find a way to know when the mouse enters on our control window and when it leaves. Unfortunately, as we know, Windows does not support these kind of events.

Using the code

The idea standing behind this source is very simple, just handle the WM_MOUSEMOVE message and capture the mouse input with the SetCapture function. So you will have to test if the pointer is actually on your window. If not you have to release the mouse (ReleaseCapture).

In order to have the OnMouseEnter & OnMouseLeave functions you have to keep a BOOL updated with TRUE whether the pointer is on the Window and FALSE when it isn't. When you try to turn on the BOOL, if it's not already TRUE you will have a MouseEnter. While, every time you call a ReleaseCapture you will have a MouseLeave.

void CMyWnd::OnMouseMove(UINT nFlags, CPoint point)
{
  SetCapture();               //  Capture the mouse input
  CRect wndRect;
  GetWndRect(&wndRect);
  ScreenToClient(&wndRect);

  if (wndRect.PtInRect(point))	
  {  // Test if the pointer is on the window
    if (m_PointerOnWnd != TRUE)	
    {
      OnMouseEnter();
      m_PointerOnWnd = TRUE;
    }
  } 
  else
  {
    ReleaseCapture();
    m_PointerOnWnd = FALSE;
  }
  CWnd::OnMouseMove(nFlags, point);
}

There's no problem even if the mouse is on the window when the application starts, because in this case Windows will automatically send a WM_MOUSEMOVE event.

That's all folks

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