552861bf30
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@16016 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
354 lines
18 KiB
TeX
354 lines
18 KiB
TeX
\chapter{Basic event handling}\label{chapbasicevents}
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\pagenumbering{arabic}%
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\setheader{{\it CHAPTER \thechapter: BASIC EVENT HANDLING}}{}{}{}{}{{\it CHAPTER \thechapter: BASIC EVENT HANDLING}}%
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\setfooter{\thepage}{}{}{}{}{\thepage}%
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\section{Introduction}
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In most cases, wxWindows uses the concept of {\it event tables} to catch user input.
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An event table is placed in an implementation file to tell wxWindows how to map
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events to member functions. These member functions are not virtual functions, but
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they are all similar in form: they take a single wxEvent-derived argument, and have a void return
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type.
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Here's an example of an event table.
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\begin{verbatim}
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BEGIN_EVENT_TABLE(MyFrame, wxFrame)
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EVT_MENU (wxID_EXIT, MyFrame::OnExit)
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EVT_MENU (DO_TEST, MyFrame::DoTest)
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EVT_SIZE ( MyFrame::OnSize)
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EVT_BUTTON (BUTTON1, MyFrame::OnButton1)
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END_EVENT_TABLE()
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\end{verbatim}
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The first two entries map menu commands to two different member functions. The EVT\_SIZE macro
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doesn't need a window identifier, since normally you are only interested in the
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current window's size events. (In fact you could intercept a particular window's size event
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by using EVT\_CUSTOM(wxEVT\_SIZE, id, func).)
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The EVT\_BUTTON macro demonstrates that the originating event does not have to come from
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the window class implementing the event table - if the event source is a button within a panel within a frame, this will still
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work, because event tables are searched up through the hierarchy of windows. In this
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case, the button's event table will be searched, then the parent panel's, then the frame's.
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As mentioned before, the member functions that handle events do not have to be virtual.
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Indeed, the member functions should not be virtual as the event handler ignores that
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the functions are virtual, i.e. overriding a virtual member function in a derived class
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will not have any effect.
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These member functions take an event argument, and the class of event differs according
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to the type of event and the class of the originating window. For size
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events, \wxhelpref{wxSizeEvent}{wxsizeevent} is used. For menu commands and most control
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commands (such as button presses), \wxhelpref{wxCommandEvent}{wxcommandevent} is used.
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When controls get more complicated, then specific event classes are used, such
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as \wxhelpref{wxTreeEvent}{wxtreeevent} for events from \wxhelpref{wxTreeCtrl}{wxtreectrl} windows.
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As well as the event table in the implementation file, there must be a DECLARE\_EVENT\_TABLE
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macro in the class definition. For example:
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{\small%
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\begin{verbatim}
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class MyFrame: public wxFrame {
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DECLARE_DYNAMIC_CLASS(MyFrame)
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public:
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...
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void OnExit(wxCommandEvent& event);
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void OnSize(wxSizeEvent& event);
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protected:
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int m_count;
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...
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DECLARE_EVENT_TABLE()
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};
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\end{verbatim}
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}%
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\section{How events are processed}\label{eventprocessing}
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When an event is received from the windowing system, wxWindows calls \wxhelpref{wxEvtHandler::ProcessEvent}{wxevthandlerprocessevent} on
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the first event handler object belonging to the window generating the event.
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It may be noted that wxWindows' event processing system implements something
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very close to virtual methods in normal C++, i.e. it is possible to alter
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the behaviour of a class by overriding its event handling functions. In
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many cases this works even for changing the behaviour of native controls.
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For example it is possible to filter out a number of key events sent by the
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system to a native text control by overriding wxTextCtrl and defining a
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handler for key events using EVT\_KEY\_DOWN. This would indeed prevent
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any key events from being sent to the native control - which might not be
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what is desired. In this case the event handler function has to call Skip()
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so as to indicate that the search for the event handler should continue.
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To summarize, instead of explicitly calling the base class version as you
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would have done with C++ virtual functions (i.e. {\it wxTextCtrl::OnChar()}),
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you should instead call \wxhelpref{wxEvent::Skip}{wxeventskip}.
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In practice, this would look like the following if the derived text control only
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accepts 'a' to 'z' and 'A' to 'Z':
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{\small%
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\begin{verbatim}
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void MyTextCtrl::OnChar(wxKeyEvent& event)
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{
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if ( isalpha( event.KeyCode() ) )
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{
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// key code is within legal range. we call event.Skip() so the
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// event can be processed either in the base wxWindows class
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// or the native control.
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event.Skip();
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}
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else
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{
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// illegal key hit. we don't call event.Skip() so the
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// event is not processed anywhere else.
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wxBell();
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}
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}
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\end{verbatim}
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}%
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The normal order of event table searching by ProcessEvent is as follows:
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\begin{enumerate}\itemsep=0pt
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\item If the object is disabled (via a call to \wxhelpref{wxEvtHandler::SetEvtHandlerEnabled}{wxevthandlersetevthandlerenabled})
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the function skips to step (6).
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\item If the object is a wxWindow, {\bf ProcessEvent} is recursively called on the window's\rtfsp
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\wxhelpref{wxValidator}{wxvalidator}. If this returns TRUE, the function exits.
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\item {\bf SearchEventTable} is called for this event handler. If this fails, the base
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class table is tried, and so on until no more tables exist or an appropriate function was found,
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in which case the function exits.
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\item The search is applied down the entire chain of event handlers (usually the chain has a length
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of one). If this succeeds, the function exits.
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\item If the object is a wxWindow and the event is a wxCommandEvent, {\bf ProcessEvent} is
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recursively applied to the parent window's event handler. If this returns TRUE, the function exits.
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\item Finally, {\bf ProcessEvent} is called on the wxApp object.
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\end{enumerate}
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{\bf Pay close attention to Step 5.} People often overlook or get
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confused by this powerful feature of the wxWindows event processing
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system. To put it a different way, events derived either directly or
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indirectly from wxCommandEvent will travel up the containment
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hierarchy from child to parent until an event handler is found that
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doesn't call event.Skip(). Events not derived from wxCommandEvent are
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sent only to the window they occurred in and then stop.
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Typically events that deal with a window as a window (size, motion,
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paint, mouse, keyboard, etc.) are sent only to the window. Events
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that have a higher level of meaning and/or are generated by the window
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itself, (button click, menu select, tree expand, etc.) are command
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events and are sent up to the parent to see if it is interested in the
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event.
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Note that your application may wish to override ProcessEvent to redirect processing of
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events. This is done in the document/view framework, for example, to allow event handlers
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to be defined in the document or view. To test for command events (which will probably
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be the only events you wish to redirect), you may use wxEvent::IsCommandEvent for
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efficiency, instead of using the slower run-time type system.
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As mentioned above, only command events are recursively applied to the parents event
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handler. As this quite often causes confusion for users, here is a list of system
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events which will {\it not} get sent to the parent's event handler:
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\begin{twocollist}\itemsep=0pt
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\twocolitem{\wxhelpref{wxEvent}{wxevent}}{The event base class}
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\twocolitem{\wxhelpref{wxActivateEvent}{wxactivateevent}}{A window or application activation event}
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\twocolitem{\wxhelpref{wxCloseEvent}{wxcloseevent}}{A close window or end session event}
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\twocolitem{\wxhelpref{wxEraseEvent}{wxeraseevent}}{An erase background event}
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\twocolitem{\wxhelpref{wxFocusEvent}{wxfocusevent}}{A window focus event}
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\twocolitem{\wxhelpref{wxKeyEvent}{wxkeyevent}}{A keypress event}
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\twocolitem{\wxhelpref{wxIdleEvent}{wxidleevent}}{An idle event}
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\twocolitem{\wxhelpref{wxInitDialogEvent}{wxinitdialogevent}}{A dialog initialisation event}
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\twocolitem{\wxhelpref{wxJoystickEvent}{wxjoystickevent}}{A joystick event}
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\twocolitem{\wxhelpref{wxMenuEvent}{wxmenuevent}}{A menu event}
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\twocolitem{\wxhelpref{wxMouseEvent}{wxmouseevent}}{A mouse event}
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\twocolitem{\wxhelpref{wxMoveEvent}{wxmoveevent}}{A move event}
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\twocolitem{\wxhelpref{wxPaintEvent}{wxpaintevent}}{A paint event}
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\twocolitem{\wxhelpref{wxQueryLayoutInfoEvent}{wxquerylayoutinfoevent}}{Used to query layout information}
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\twocolitem{\wxhelpref{wxSizeEvent}{wxsizeevent}}{A size event}
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\twocolitem{\wxhelpref{wxScrollWinEvent}{wxscrollwinevent}}{A scroll event sent by a scrolled window (not a scroll bar)}
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\twocolitem{\wxhelpref{wxSysColourChangedEvent}{wxsyscolourchangedevent}}{A system colour change event}
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\twocolitem{\wxhelpref{wxUpdateUIEvent}{wxupdateuievent}}{A user interface update event}
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\end{twocollist}
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In some cases, it might be desired by the programmer to get a certain number
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of system events in a parent window, for example all key events sent to, but not
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used by, the native controls in a dialog. In this case, a special event handler
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will have to be written that will override ProcessEvent() in order to pass
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all events (or any selection of them) to the parent window.
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% VZ: it doesn't work like this, but just in case we ever reenable this
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% behaviour, I leave it here
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%
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% \section{Redirection of command events to the window with the focus}
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%
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% The usual upward search through the window hierarchy for command event
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% handlers does not always meet an application's requirements. Say you have two
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% wxTextCtrl windows in a frame, plus a toolbar with Cut, Copy and Paste
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% buttons. To avoid the need to define event handlers in the frame
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% and redirect them explicitly to the window with the focus, command events
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% are sent to the window with the focus first, for
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% menu and toolbar command and UI update events only. This means that
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% each window can handle its own commands and UI updates independently. In
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% fact wxTextCtrl can handle Cut, Copy, Paste, Undo and Redo commands and UI update
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% requests, so no extra coding is required to support them in your menus and
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% toolbars.
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\section{Pluggable event handlers}
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In fact, you don't have to derive a new class from a window class
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if you don't want to. You can derive a new class from wxEvtHandler instead,
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defining the appropriate event table, and then call
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\rtfsp\wxhelpref{wxWindow::SetEventHandler}{wxwindowseteventhandler} (or, preferably,
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\rtfsp\wxhelpref{wxWindow::PushEventHandler}{wxwindowpusheventhandler}) to make this
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event handler the object that responds to events. This way, you can avoid
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a lot of class derivation, and use the same event handler object to
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handle events from instances of different classes. If you ever have to call a window's event handler
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manually, use the GetEventHandler function to retrieve the window's event handler and use that
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to call the member function. By default, GetEventHandler returns a pointer to the window itself
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unless an application has redirected event handling using SetEventHandler or PushEventHandler.
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One use of PushEventHandler is to temporarily or permanently change the
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behaviour of the GUI. For example, you might want to invoke a dialog editor
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in your application that changes aspects of dialog boxes. You can
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grab all the input for an existing dialog box, and edit it `in situ',
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before restoring its behaviour to normal. So even if the application
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has derived new classes to customize behaviour, your utility can indulge
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in a spot of body-snatching. It could be a useful technique for on-line
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tutorials, too, where you take a user through a serious of steps and
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don't want them to diverge from the lesson. Here, you can examine the events
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coming from buttons and windows, and if acceptable, pass them through to
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the original event handler. Use PushEventHandler/PopEventHandler
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to form a chain of event handlers, where each handler processes a different
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range of events independently from the other handlers.
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\section{Window identifiers}\label{windowids}
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\index{identifiers}\index{wxID}Window identifiers are integers, and are used to uniquely determine window identity in the
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event system (though you can use it for other purposes). In fact, identifiers do not need
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to be unique across your entire application just so long as they are unique within a particular context you're interested
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in, such as a frame and its children. You may use the wxID\_OK identifier, for example, on
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any number of dialogs so long as you don't have several within the same dialog.
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If you pass -1 to a window constructor, an identifier will be generated for you, but beware:
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if things don't respond in the way they should, it could be because of an id conflict. It is safer
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to supply window ids at all times. Automatic generation of identifiers starts at 1 so may well conflict
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with your own identifiers.
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The following standard identifiers are supplied. You can use wxID\_HIGHEST to determine the
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number above which it is safe to define your own identifiers. Or, you can use identifiers below
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wxID\_LOWEST.
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\begin{verbatim}
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#define wxID_LOWEST 4999
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#define wxID_OPEN 5000
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#define wxID_CLOSE 5001
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#define wxID_NEW 5002
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#define wxID_SAVE 5003
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#define wxID_SAVEAS 5004
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#define wxID_REVERT 5005
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#define wxID_EXIT 5006
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#define wxID_UNDO 5007
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#define wxID_REDO 5008
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#define wxID_HELP 5009
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#define wxID_PRINT 5010
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#define wxID_PRINT_SETUP 5011
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#define wxID_PREVIEW 5012
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#define wxID_ABOUT 5013
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#define wxID_HELP_CONTENTS 5014
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#define wxID_HELP_COMMANDS 5015
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#define wxID_HELP_PROCEDURES 5016
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#define wxID_HELP_CONTEXT 5017
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#define wxID_CUT 5030
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#define wxID_COPY 5031
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#define wxID_PASTE 5032
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#define wxID_CLEAR 5033
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#define wxID_FIND 5034
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#define wxID_DUPLICATE 5035
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#define wxID_SELECTALL 5036
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#define wxID_FILE1 5050
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#define wxID_FILE2 5051
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#define wxID_FILE3 5052
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#define wxID_FILE4 5053
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#define wxID_FILE5 5054
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#define wxID_FILE6 5055
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#define wxID_FILE7 5056
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#define wxID_FILE8 5057
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#define wxID_FILE9 5058
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#define wxID_OK 5100
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#define wxID_CANCEL 5101
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#define wxID_APPLY 5102
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#define wxID_YES 5103
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#define wxID_NO 5104
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#define wxID_STATIC 5105
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#define wxID_HIGHEST 5999
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\end{verbatim}
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\section{Event macros summary}\label{eventmacros}
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\wxheading{Generic event table macros}
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\twocolwidtha{8cm}%
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\begin{twocollist}\itemsep=0pt
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\twocolitem{\windowstyle{EVT\_CUSTOM(event, id, func)}}{Allows you to add a custom event table
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entry by specifying the event identifier (such as wxEVT\_SIZE), the window identifier,
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and a member function to call.}
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\twocolitem{\windowstyle{EVT\_CUSTOM\_RANGE(event, id1, id2, func)}}{The same as EVT\_CUSTOM,
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but responds to a range of window identifiers.}
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\twocolitem{\windowstyle{EVT\_COMMAND(id, event, func)}}{The same as EVT\_CUSTOM, but
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expects a member function with a wxCommandEvent argument.}
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\twocolitem{\windowstyle{EVT\_COMMAND\_RANGE(id1, id2, event, func)}}{The same as EVT\_CUSTOM\_RANGE, but
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expects a member function with a wxCommandEvent argument.}
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\end{twocollist}
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\wxheading{Macros listed by event class}
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The documentation for specific event macros is organised by event class. Please refer
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to these sections for details.
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\twocolwidtha{8cm}%
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\begin{twocollist}\itemsep=0pt
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\twocolitem{\wxhelpref{wxActivateEvent}{wxactivateevent}}{The EVT\_ACTIVATE and EVT\_ACTIVATE\_APP macros intercept
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activation and deactivation events.}
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\twocolitem{\wxhelpref{wxCommandEvent}{wxcommandevent}}{A range of commonly-used control events.}
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\twocolitem{\wxhelpref{wxCloseEvent}{wxcloseevent}}{The EVT\_CLOSE macro handles window closure
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called via \wxhelpref{wxWindow::Close}{wxwindowclose}.}
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\twocolitem{\wxhelpref{wxDropFilesEvent}{wxdropfilesevent}}{The EVT\_DROP\_FILES macros handles
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file drop events.}
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\twocolitem{\wxhelpref{wxEraseEvent}{wxeraseevent}}{The EVT\_ERASE\_BACKGROUND macro is used to handle window erase requests.}
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\twocolitem{\wxhelpref{wxFocusEvent}{wxfocusevent}}{The EVT\_SET\_FOCUS and EVT\_KILL\_FOCUS macros are used to handle keyboard focus events.}
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\twocolitem{\wxhelpref{wxKeyEvent}{wxkeyevent}}{EVT\_CHAR and EVT\_CHAR\_HOOK macros handle keyboard
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input for any window.}
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\twocolitem{\wxhelpref{wxIdleEvent}{wxidleevent}}{The EVT\_IDLE macro handle application idle events
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(to process background tasks, for example).}
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\twocolitem{\wxhelpref{wxInitDialogEvent}{wxinitdialogevent}}{The EVT\_INIT\_DIALOG macro is used
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to handle dialog initialisation.}
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\twocolitem{\wxhelpref{wxListEvent}{wxlistevent}}{These macros handle \wxhelpref{wxListCtrl}{wxlistctrl} events.}
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\twocolitem{\wxhelpref{wxMenuEvent}{wxmenuevent}}{These macros handle special menu events (not menu commands).}
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\twocolitem{\wxhelpref{wxMouseEvent}{wxmouseevent}}{Mouse event macros can handle either individual
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mouse events or all mouse events.}
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\twocolitem{\wxhelpref{wxMoveEvent}{wxmoveevent}}{The EVT\_MOVE macro is used to handle a window move.}
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\twocolitem{\wxhelpref{wxPaintEvent}{wxpaintevent}}{The EVT\_PAINT macro is used to handle window paint requests.}
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\twocolitem{\wxhelpref{wxScrollEvent}{wxscrollevent}}{These macros are used to handle scroll events from
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\wxhelpref{wxScrollBar}{wxscrollbar}, \wxhelpref{wxSlider}{wxslider},and \wxhelpref{wxSpinButton}{wxspinbutton}.}
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\twocolitem{\wxhelpref{wxSizeEvent}{wxsizeevent}}{The EVT\_SIZE macro is used to handle a window resize.}
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\twocolitem{\wxhelpref{wxSplitterEvent}{wxsplitterevent}}{The EVT\_SPLITTER\_SASH\_POS\_CHANGED, EVT\_SPLITTER\_UNSPLIT
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and EVT\_SPLITTER\_DCLICK macros are used to handle the various splitter window events.}
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\twocolitem{\wxhelpref{wxSysColourChangedEvent}{wxsyscolourchangedevent}}{The EVT\_SYS\_COLOUR\_CHANGED macro is used to handle
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events informing the application that the user has changed the system colours (Windows only).}
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\twocolitem{\wxhelpref{wxTreeEvent}{wxtreeevent}}{These macros handle \wxhelpref{wxTreeCtrl}{wxtreectrl} events.}
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\twocolitem{\wxhelpref{wxUpdateUIEvent}{wxupdateuievent}}{The EVT\_UPDATE\_UI macro is used to handle user interface
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update pseudo-events, which are generated to give the application the chance to update the visual state of menus,
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toolbars and controls.}
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\end{twocollist}
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