在切分窗口之间实现拖放(2)

　　现在到目录树视了：

　　为了能访问需要的成员变量，我们还是先定义了一个帮助函数从而可以轻易的访问我们的app类：

CMyApp *CMyTreeView::GetApp()
{
　return ( (CMyApp*)AfxGetApp() );
}

　　三个消息处理函数：

ON_WM_LBUTTONUP()
ON_WM_MOUSEMOVE()
ON_NOTIFY_REFLECT(LVN_BEGINDRAG, OnBegindrag)

　　把这个视所能设置的元素都设成是开始拖的状态，而目的视也许是本身，或是别的视。

void CMyTreeView::OnBegindrag(NMHDR* pNMHDR, LRESULT* pResult)
{
　NM_TREEVIEW *pTreeView = (NM_TREEVIEW*)pNMHDR;

　*pResult = 0;

　//获得指向树型控件的指针:
　CTreeCtrl &cTree = GetTreeCtrl();

　GetApp()->cTreeItemDrag = pTreeView->itemNew.hItem;
　GetApp()->cTreeItemDrop = NULL;

　//建立一个被拖的条目的图象:
　GetApp()->cpDragImage = cTree.CreateDragImage(GetApp()->cTreeItemDrag);
　GetApp()->cpDragImage->BeginDrag(0, CPoint(-15,-15));
　POINT pt = pTreeView->ptDrag;
　ClientToScreen( &pt );
　GetApp()->cpDragImage->DragEnter(NULL, pt);

　//初始化:
　GetApp()->cDragging = TRUE;
　GetApp()->cpDragWnd = &cTree;
　GetApp()->cpDropWnd = NULL;
　}

void CMyTreeView::OnMouseMove(UINT nFlags, CPoint point)
{
　HTREEITEM hitem;
　UINT flags;

　//获得指向树型控件的指针:
　CTreeCtrl &cTree = GetTreeCtrl();

　//如果是正在被拖动的话：
　if ( GetApp()->cDragging )
　{
　　POINT pt = point;
　　ClientToScreen( &pt );