Advanced MFC Programming

Chapter 5. Common Controls
void MCTreeCtrl::OnBegindrag(NMHDR *pNMHDR, LRESULT *pResult)
{
CPoint pt;
UINT nFlags;
……
NM_TREEVIEW *pNMTreeView=(NM_TREEVIEW *)pNMHDR;
::GetCursorPos(&pt);
ScreenToClient(&pt);
ASSERT(m_bIsDragging == FALSE);
m_bIsDragging=TRUE;
m_hTreeDragSrc=HitTest(pt, &nFlags);
m_hTreeDragTgt=NULL;
Next, we need to obtain dragging image list for this node. The dragging image list is created by calling
function CTreeCtrl::CreateDragImage(…). After this, the address of the image list object is stored in
variable m_pilDrag. If the image list is created successfully, we call several member functions of
CImageList to display the dragging image and enter dragging mode. If not, we should not start dragging,
and need to set the content of pResult to a non-zero value, this will stop dragging:
……
}
ASSERT(m_pilDrag == NULL);
m_pilDrag=CreateDragImage(m_hTreeDragSrc);
if(m_pilDrag != NULL)
{
m_pilDrag->DragShowNolock(TRUE);
m_pilDrag->SetDragCursorImage(0, CPoint(0, 0));
m_pilDrag->BeginDrag(0, CPoint(0,0));
m_pilDrag->DragMove(pt);
m_pilDrag->DragEnter(this, pt);
SetCapture();
*pResult=0;
}
else
{
m_bIsDragging=FALSE;
*pResult=1;
}
WM_MOUSEMOVE
Then we need to implement WM_MOUSEMOVE message handler. Whenever the mouse cursor moves to a
new place, we need to call function CImageList::DragMove(…) to move the dragging image so that the
image will always follow the mouse’s movement. We need to check if the mouse hits a new node by
calling function CTreeCtrl::HitTest(…). If so, we must leave dragging mode by calling function
CImageList:: DragLeave(…), highlight the new node by calling function
CTreeCtrl::SelectDropTarget(…), and enter dragging mode again by calling function
CTreeCtrl::DragEnter(…). The reason for doing this is that when dragging is undergoing, the tree control
window is locked and no update could be implemented successfully. The following is the implementation
of this message handler:
void MCTreeCtrl::OnMouseMove(UINT nFlags, CPoint point)
{
HTREEITEM
hitem;
UINT
flags;
if(m_bIsDragging)
{
ASSERT(m_pilDrag != NULL);
m_pilDrag->DragMove(point);
if((hitem=HitTest(point, &flags)) != NULL)
{
m_pilDrag->DragLeave(this);
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