Advanced MFC Programming

Chapter 5. Common Controls
typedef struct _NM_TREEVIEW{
NMHDR hdr;
UINT action;
TV_ITEM itemOld;
TV_ITEM itemNew;
POINT ptDrag;
} NM_TREEVIEW;
The most important member of this structure is action, it could be either TVE_EXPAND (indicating the
node is about to expand) or TVE_COLLAPSE (indicating the node is about to collapse). Two other useful
members are itemOld and itemNew, both of them are TV_ITEM type objects and contain old and new states
of the node respectively. We can check iImage member of itemNew to see if the associated image is 2 or 3
(Indices 2 and 3 correspond to image IDB_BITMAP_CLOSED_FOLDER and IDB_BITMAP_OPENFOLDER
respectively, which indicate that the node represents a folder. In the sample, we will not change other
node’s image when they are being expanded or collapsed), if so, we need to call function
CTreeCtrl::SetItemImage(…) to change the image of the node if necessary.
We can handle this message either within class CTreeCtrl or CDialog. Handling the message in
CTreeCtrl has the advantage that once the feature is implemented, we can reuse this class in other
applications without adding additional code.
In the sample, a new class MCTreeCtrl is designed for this purpose. It is added to the application
through using Class Wizard. Also, message handlers MCTreeCtrl::OnItemexpanding(…) and
MCTreeCtrl::OnEndlabeledit(…) are added to dynamically change node’s associated images and enable
label editing (Label editing will be discussed later).
The following is the implementation of function MCTreeCtrl::OnItemexpanding(…):
void MCTreeCtrl::OnItemexpanding(NMHDR* pNMHDR, LRESULT *pResult)
{
NM_TREEVIEW* pNMTreeView = (NM_TREEVIEW*)pNMHDR;
}
if
(
)
{
}
if
(
)
{
pNMTreeView->action == TVE_EXPAND &&
pNMTreeView->itemNew.iImage == 2
SetItemImage(pNMTreeView->itemNew.hItem, 3, 3);
pNMTreeView->action == TVE_COLLAPSE &&
pNMTreeView->itemNew.iImage == 3
SetItemImage(pNMTreeView->itemNew.hItem, 2, 2);
}
*pResult = 0;
If the node is about to expand and its associated image is 2, we associate image 3 with this node. This
is implemented through calling function CTreeCtrl::SetItemImage(…), which has the following format:
BOOL CTreeCtrl::SetItemImage(HTREEITEM hItem, int nImage, int nSelectedImage);
The first parameter of this function is the handle of tree control, which can be obtained from
pNMTreeView->itemNew.hItem. Similarly, if the node is about to collapse and its associated image is 3, we
call this function to associate image 2 with this node.
Handling TVN_ENDLABELEDIT to Enable Label Editing
The next feature we want to add is label editing. If we are familiar with “Explorer” application in
Windows95, we know that the file or directory names (which are node labels) can be edited dynamically
by single clicking on it.
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