1. wxNotifyEvent documented

2. wxNotebook event now derives from it under wxGTK too - fixing the
   PAGE_CHANGING event handling bug
3. the controls sample demonstrates PAGE_CHANGING in action


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@2562 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/latex/wx/noteevt.tex

@@ -1,9 +1,24 @@
 \section{\class{wxNotebookEvent}}\label{wxnotebookevent}
 
-This class represents the events generated by a notebook control.
+This class represents the events generated by a notebook control: currently,
+there are two of them. The PAGE\_CHANGING event is sent before the current
+page is changed. It allows to the program to examine the current page (which
+can be retrieved with 
+\helpref{GetOldSelection()}wxnotebookeventgetoldselection}) and to veto the page
+change by calling \helpref{Veto()}{wxnotifyeventveto} if, for example, the
+current values in the controls of the old page are invalid.
+
+The second event - PAGE\_CHANGED - is sent after the page has been changed and
+the program cannot veto it any more, it just informs it about the page change.
+
+To summarize, if the program is interested in validating the page values
+before allowing the user to change it, it should process the PAGE\_CHANGING
+event, otherwise PAGE\_CHANGED is probably enough. In any case, it is probably
+unnecessary to process both events at once.
 
 \wxheading{Derived from}
 
+\helpref{wxNotifyEvent}{wxnotifyevent}\\
 \helpref{wxCommandEvent}{wxcommandevent}\\
 \helpref{wxEvent}{wxevent}\\
 \helpref{wxEvtHandler}{wxevthandler}\\
@@ -37,7 +52,7 @@ Processes a wxEVT\_COMMAND\_NOTEBOOK\_PAGE\_CHANGING event.}
 \func{}{wxNotebookEvent}{\param{wxEventType}{ eventType = wxEVT\_NULL},
  \param{int}{ id = 0}, \param{int}{ sel = -1}, \param{int}{ oldSel = -1}}
 
-Constructor.
+Constructor (used internally by wxWindows only).
 
 \membersection{wxNotebookEvent::GetOldSelection}\label{wxnotebookeventgetoldselection}