Advanced MFC Programming

Chapter 5. Common Controls
Parameter
pWndLock
Meaning
The window that has been locked during the dragging.
BOOL CTreeCtrl::SelectDropTarget(HTREEITEM hItem);
Parameter
hItem
Meaning
Handle of the node that is to be highlighted.
When the mouse button is released, we need to check if the source node can be copied to the target
node. In the sample, we disable copying under the following three conditions: 1) The source node is the
same with the target node. 2) The target node is a descendent node of the source node. 3) The target node
does not have any child node. By setting these restrictions, a node can only be copied to become the child
of its parent node (direct or indirect).
We can use function CTreeCtrl::GetParentItem(…) to decide if one node is the descendent of
another node:
HTREEITEM CTreeCtrl::GetParentItem(HTREEITEM hItem);
This function will return an HTREEITEM handle, which specifies the parent of node hItem. By
repeatedly calling this function we will finally get a NULL return value (This indicates that the root node
was encountered). Using this method, we can easily find out a list of all nodes that are parents of a specific
node.
New Member Variables and Functions
To implement drag-n-drop, several new variables and functions are declared in class MCTreeCtrl:
……
……
class MCTreeCtrl : public CTreeCtrl
{
public:
void CopyItemTo(HTREEITEM, HTREEITEM);
BOOL IsDescendent(HTREEITEM, HTREEITEM);
//{{AFX_VIRTUAL(MCTreeCtrl)
//}}AFX_VIRTUAL
protected:
BOOL m_bIsDragging;
CImageList *m_pilDrag;
HTREEITEM m_hTreeDragSrc;
HTREEITEM m_hTreeDragTgt;
};
Here, Boolean type variable m_bIsDragging is used to indicate if the drag-n-drop activity is
undergoing. Pointer m_pilDrag will be used to store the dragging image. Variables m_hTreeDragSrc and
m_hTreeDragTgt are used to store the handles of source and target nodes respectively. We can use them to
implement copying right after the source node is dropped. Function MCTreeCtrl::IsDescendent(…) is
used to judge if one node is the descendent node of another, and MCTreeCtrl::CopyItemTo(…) will copy
one node (and all its descendent nodes) to another place.
Node Copy
When copying a node, we want to copy not only the node itself, but also all its descendent nodes. Since
we do not know how many descendents a node have beforehand, we need to call function
MCTreeCtrl::CopyItemTo(…) recursively until all the descendent nodes are copied. The following is the
implementation of this function:
void MCTreeCtrl::CopyItemTo(HTREEITEM hTreeDragTgt, HTREEITEM hTreeDragSrc)
{
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