Using ESC to cancel drag and drop

BOOL CTreeCtrlX::PreTranslateMessage(MSG* pMsg)
{
	if( pMsg->message == WM_KEYDOWN && pMsg->wParam == VK_ESCAPE 
					&& m_bLDragging)
	{
		m_bLDragging = 0;
		CImageList::DragLeave(NULL);
		CImageList::EndDrag();
		ReleaseCapture();
		SelectDropTarget(NULL);
		delete m_pDragImage;
		return TRUE;		// DO NOT process further
	}

	return CTreeCtrl::PreTranslateMessage(pMsg);
}

There is one more thing you need to for this to work properly - call SetFocus() in your WM_LBUTTONDOWN handler. If the control doesn't already have focus when the user begins the drag and drop operation, then the control doesn't receive focus and if the control doesn't have the focus, it doesn't receive the WM_KEYDOWN message.