An event table is placed in an implementation file to tell wxWindows how to map
events to member functions. These member functions are not virtual functions, but
-they all similar in form: they take a single wxEvent-derived argument, and have a void return
+they are all similar in form: they take a single wxEvent-derived argument, and have a void return
type.
Here's an example of an event table.
\subsection{How events are processed}\label{eventprocessing}
-When an event is received from the windowing system, wxWindows calls \helpref{wxEvtHandler::ProcessEvent}{wxevthandlerprocessevent} on
-the first event handler object belonging to the window generating the event.
+When an event is received from the windowing system, wxWindows calls
+\helpref{wxEvtHandler::ProcessEvent}{wxevthandlerprocessevent} on the first
+event handler object belonging to the window generating the event.
It may be noted that wxWindows' event processing system implements something
very close to virtual methods in normal C++, i.e. it is possible to alter
handler for key events using EVT\_KEY\_DOWN. This would indeed prevent
any key events from being sent to the native control - which might not be
what is desired. In this case the event handler function has to call Skip()
-so as to indicate that it did NOT handle the event at all.
+so as to indicate that the search for the event handler should continue.
+
+To summarize, instead of explicitly calling the base class version as you
+would have done with C++ virtual functions (i.e. {\it wxTextCtrl::OnChar()}),
+you should instead call \helpref{Skip}{wxeventskip}.
In practice, this would look like this if the derived text control only
accepts 'a' to 'z' and 'A' to 'Z':
// key code is within legal range. we call event.Skip() so the
// event can be processed either in the base wxWindows class
// or the native control.
-
- event.Skip();
+
+ event.Skip();
}
else
{
// illegal key hit. we don't call event.Skip() so the
// event is not processed anywhere else.
-
+
wxBell();
}
}
\item Finally, {\bf ProcessEvent} is called on the wxApp object.
\end{enumerate}
+{\bf Pay close attention to Step 5.} People often overlook or get
+confused by this powerful feature of the wxWindows event processing
+system. To put it a different way, events derived either directly or
+indirectly from wxCommandEvent will travel up the containment
+hierarchy from child to parent until an event handler is found that
+doesn't call event.Skip(). Events not derived from wxCommandEvent are
+sent only to the window they occurred in and then stop.
+
+Finally, there is another additional complication (which, in fact, simplifies
+life of wxWindows programmers significantly): when propagating the command
+events upwards to the parent window, the event propagation stops when it
+reaches the parent dialog, if any. This means that you don't risk to get
+unexpected events from the dialog controls (which might be left unprocessed by
+the dialog itself because it doesn't care about them) when a modal dialog is
+popped up. The events do propagate beyond the frames, however. The rationale
+for this choice is that there are only a few frames in a typical application
+and their parent-child relation are well understood by the programmer while it
+may be very difficult, if not impossible, to track down all the dialogs which
+may be popped up in a complex program (remember that some are created
+automatically by wxWindows). If you need to specify a different behaviour for
+some reason, you can use
+\helpref{SetExtraStyle(wxWS\_EX\_BLOCK\_EVENTS)}{wxwindowsetextrastyle}
+explicitly to prevent the events from being propagated beyond the given window
+or unset this flag for the dialogs which have it on by default.
+
+Typically events that deal with a window as a window (size, motion,
+paint, mouse, keyboard, etc.) are sent only to the window. Events
+that have a higher level of meaning and/or are generated by the window
+itself, (button click, menu select, tree expand, etc.) are command
+events and are sent up to the parent to see if it is interested in the
+event.
+
Note that your application may wish to override ProcessEvent to redirect processing of
events. This is done in the document/view framework, for example, to allow event handlers
-to be defined in the document or view.
+to be defined in the document or view. To test for command events (which will probably
+be the only events you wish to redirect), you may use wxEvent::IsCommandEvent for
+efficiency, instead of using the slower run-time type system.
As mentioned above, only command events are recursively applied to the parents event
handler. As this quite often causes confusion for users, here is a list of system
\twocolitem{\helpref{wxPaintEvent}{wxpaintevent}}{A paint event}
\twocolitem{\helpref{wxQueryLayoutInfoEvent}{wxquerylayoutinfoevent}}{Used to query layout information}
\twocolitem{\helpref{wxSizeEvent}{wxsizeevent}}{A size event}
+\twocolitem{\helpref{wxScrollWinEvent}{wxscrollwinevent}}{A scroll event sent by a scrolled window (not a scroll bar)}
\twocolitem{\helpref{wxSysColourChangedEvent}{wxsyscolourchangedevent}}{A system colour change event}
\twocolitem{\helpref{wxUpdateUIEvent}{wxupdateuievent}}{A user interface update event}
\end{twocollist}
of system events in a parent window, for example all key events sent to, but not
used by, the native controls in a dialog. In this case, a special event handler
will have to be written that will override ProcessEvent() in order to pass
-all events (or any selection of them) to the parent window. See next section.
+all events (or any selection of them) to the parent window.
+
+% VZ: it doesn't work like this, but just in case we ever reenable this
+% behaviour, I leave it here
+%
+% \subsection{Redirection of command events to the window with the focus}
+%
+% The usual upward search through the window hierarchy for command event
+% handlers does not always meet an application's requirements. Say you have two
+% wxTextCtrl windows in a frame, plus a toolbar with Cut, Copy and Paste
+% buttons. To avoid the need to define event handlers in the frame
+% and redirect them explicitly to the window with the focus, command events
+% are sent to the window with the focus first, for
+% menu and toolbar command and UI update events only. This means that
+% each window can handle its own commands and UI updates independently. In
+% fact wxTextCtrl can handle Cut, Copy, Paste, Undo and Redo commands and UI update
+% requests, so no extra coding is required to support them in your menus and
+% toolbars.
\subsection{Pluggable event handlers}
any number of dialogs so long as you don't have several within the same dialog.
If you pass -1 to a window constructor, an identifier will be generated for you, but beware:
-if things don't respond in the way they should, it could be because of an id conflict. It's safer
+if things don't respond in the way they should, it could be because of an id conflict. It is safer
to supply window ids at all times. Automatic generation of identifiers starts at 1 so may well conflict
with your own identifiers.
\twocolitem{\helpref{wxDropFilesEvent}{wxdropfilesevent}}{The EVT\_DROP\_FILES macros handles
file drop events.}
\twocolitem{\helpref{wxEraseEvent}{wxeraseevent}}{The EVT\_ERASE\_BACKGROUND macro is used to handle window erase requests.}
-\twocolitem{\helpref{wxFocusEvent}{wxfocusevent}}{The EVT\_SET\_FOCUS and EVT\_KILL\_FOCUS macros are used to handle keybaord focus events.}
-\twocolitem{\helpref{wxKeyEvent}{wxkeyevent}}{EVT\_CHAR and EVT\_CHAR\_HOOK macros handle keyboard
-input for any window.}
+\twocolitem{\helpref{wxFocusEvent}{wxfocusevent}}{The EVT\_SET\_FOCUS and EVT\_KILL\_FOCUS macros are used to handle keyboard focus events.}
+\twocolitem{\helpref{wxKeyEvent}{wxkeyevent}}{EVT\_CHAR, EVT\_KEY\_DOWN and
+EVT\_KEY\_UP macros handle keyboard input for any window.}
\twocolitem{\helpref{wxIdleEvent}{wxidleevent}}{The EVT\_IDLE macro handle application idle events
(to process background tasks, for example).}
\twocolitem{\helpref{wxInitDialogEvent}{wxinitdialogevent}}{The EVT\_INIT\_DIALOG macro is used
\twocolitem{\helpref{wxMouseEvent}{wxmouseevent}}{Mouse event macros can handle either individual
mouse events or all mouse events.}
\twocolitem{\helpref{wxMoveEvent}{wxmoveevent}}{The EVT\_MOVE macro is used to handle a window move.}
-\twocolitem{\helpref{wxUpdateUIEvent}{wxupdateuievent}}{The EVT\_UPDATE\_UI macro is used to handle user interface
-update pseudo-events, which are generated to give the application the chance to update the visual state of menus,
-toolbars and controls.}
\twocolitem{\helpref{wxPaintEvent}{wxpaintevent}}{The EVT\_PAINT macro is used to handle window paint requests.}
-\twocolitem{\helpref{wxScrollEvent}{wxscrollevent}}{These macros are used to handle scroll events from
-windows, \helpref{wxScrollBar}{wxscrollbar}, and \helpref{wxSpinButton}{wxspinbutton}.}
+\twocolitem{\helpref{wxScrollEvent}{wxscrollevent}}{These macros are used to handle scroll events from
+\helpref{wxScrollBar}{wxscrollbar}, \helpref{wxSlider}{wxslider},and \helpref{wxSpinButton}{wxspinbutton}.}
\twocolitem{\helpref{wxSizeEvent}{wxsizeevent}}{The EVT\_SIZE macro is used to handle a window resize.}
+\twocolitem{\helpref{wxSplitterEvent}{wxsplitterevent}}{The EVT\_SPLITTER\_SASH\_POS\_CHANGED, EVT\_SPLITTER\_UNSPLIT
+and EVT\_SPLITTER\_DOUBLECLICKED macros are used to handle the various splitter window events.}
\twocolitem{\helpref{wxSysColourChangedEvent}{wxsyscolourchangedevent}}{The EVT\_SYS\_COLOUR\_CHANGED macro is used to handle
events informing the application that the user has changed the system colours (Windows only).}
\twocolitem{\helpref{wxTreeEvent}{wxtreeevent}}{These macros handle \helpref{wxTreeCtrl}{wxtreectrl} events.}
+\twocolitem{\helpref{wxUpdateUIEvent}{wxupdateuievent}}{The EVT\_UPDATE\_UI macro is used to handle user interface
+update pseudo-events, which are generated to give the application the chance to update the visual state of menus,
+toolbars and controls.}
\end{twocollist}
projects / wxWidgets.git / blobdiff