The TVN_ITEMEXPANDING notification message notifies a tree-view control's parent window that a parent item's list of child items is about to expand or collapse. This notification message is sent in the form of a WM_NOTIFY message.
TVN_ITEMEXPANDING
pnmtv = (NM_TREEVIEW FAR *) lParam
Parameters
pnmtv
Pointer to an NM_TREEVIEW structure. The itemNew member is a TV_ITEM structure that contains valid information about the parent item in the hItem, state, and lParam members. The action member indicates whether the list is to expand or collapse. For a list of possible values, see the description of the TVM_EXPAND message.
Return Values
Returns TRUE to prevent the list from expanding or collapsing.
See Also