docs/latex/wx/tevent.tex

   1 \section{Event handling overview}\label{eventhandlingoverview}
   2
   3 Classes: \helpref{wxEvtHandler}{wxevthandler}, \helpref{wxWindow}{wxwindow}, \helpref{wxEvent}{wxevent}
   4
   5 \subsection{Introduction}\label{eventintroduction}
   6
   7 Before version 2.0 of wxWidgets, events were handled by the application
   8 either by supplying callback functions, or by overriding virtual member
   9 functions such as {\bf OnSize}.
  10
  11 From wxWidgets 2.0, {\it event tables} are used instead, with a few exceptions.
  12
  13 An event table is placed in an implementation file to tell wxWidgets how to map
  14 events to member functions. These member functions are not virtual functions, but
  15 they are all similar in form: they take a single wxEvent-derived argument, and have a void return
  16 type.
  17
  18 Here's an example of an event table.
  19
  20 \begin{verbatim}
  21 BEGIN_EVENT_TABLE(MyFrame, wxFrame)
  22   EVT_MENU    (wxID_EXIT, MyFrame::OnExit)
  23   EVT_MENU    (DO_TEST,   MyFrame::DoTest)
  24   EVT_SIZE    (           MyFrame::OnSize)
  25   EVT_BUTTON  (BUTTON1,   MyFrame::OnButton1)
  26 END_EVENT_TABLE()
  27 \end{verbatim}
  28
  29 The first two entries map menu commands to two different member functions. The
  30 EVT\_SIZE macro doesn't need a window identifier, since normally you are only
  31 interested in the current window's size events.
  32
  33 The EVT\_BUTTON macro demonstrates that the originating event does not have to
  34 come from the window class implementing the event table -- if the event source
  35 is a button within a panel within a frame, this will still work, because event
  36 tables are searched up through the hierarchy of windows for the command events.
  37 In this case, the button's event table will be searched, then the parent
  38 panel's, then the frame's.
  39
  40 As mentioned before, the member functions that handle events do not have to be
  41 virtual. Indeed, the member functions should not be virtual as the event
  42 handler ignores that the functions are virtual, i.e. overriding a virtual
  43 member function in a derived class will not have any effect. These member
  44 functions take an event argument, and the class of event differs according to
  45 the type of event and the class of the originating window. For size events,
  46 \helpref{wxSizeEvent}{wxsizeevent} is used. For menu commands and most
  47 control commands (such as button presses),
  48 \helpref{wxCommandEvent}{wxcommandevent} is used. When controls get more
  49 complicated, then specific event classes are used, such as
  50 \helpref{wxTreeEvent}{wxtreeevent} for events from
  51 \helpref{wxTreeCtrl}{wxtreectrl} windows.
  52
  53 As well as the event table in the implementation file, there must also be a
  54 DECLARE\_EVENT\_TABLE macro somewhere in the class declaration. For example:
  55
  56 {\small%
  57 \begin{verbatim}
  58 class MyFrame : public wxFrame
  59 {
  60 public:
  61   ...
  62   void OnExit(wxCommandEvent& event);
  63   void OnSize(wxSizeEvent& event);
  64
  65 protected:
  66   int       m_count;
  67   ...
  68
  69   DECLARE_EVENT_TABLE()
  70 };
  71 \end{verbatim}
  72 }%
  73
  74 Note that this macro may occur in any section of the class (public, protected
  75 or private) but that it is probably better to insert it at the end, as shown,
  76 because this macro implicitly changes the access to protected which may be
  77 quite unexpected if there is anything following it.
  78
  79 Finally, if you don't like using macros for static initialization of the event
  80 tables you may also use \helpref{wxEvtHandler::Connect}{wxevthandlerconnect} to
  81 connect the events to the handlers dynamically, during run-time. See the
  82 \helpref{event sample}{sampleevent} for an example of doing it.
  83
  84
  85 \subsection{How events are processed}\label{eventprocessing}
  86
  87 When an event is received from the windowing system, wxWidgets calls
  88 \helpref{wxEvtHandler::ProcessEvent}{wxevthandlerprocessevent} on the first
  89 event handler object belonging to the window generating the event.
  90
  91 It may be noted that wxWidgets' event processing system implements something
  92 very close to virtual methods in normal C++, i.e. it is possible to alter
  93 the behaviour of a class by overriding its event handling functions. In
  94 many cases this works even for changing the behaviour of native controls.
  95 For example it is possible to filter out a number of key events sent by the
  96 system to a native text control by overriding wxTextCtrl and defining a
  97 handler for key events using EVT\_KEY\_DOWN. This would indeed prevent
  98 any key events from being sent to the native control - which might not be
  99 what is desired. In this case the event handler function has to call Skip()
 100 so as to indicate that the search for the event handler should continue.
 101
 102 To summarize, instead of explicitly calling the base class version as you
 103 would have done with C++ virtual functions (i.e. {\it wxTextCtrl::OnChar()}),
 104 you should instead call \helpref{Skip}{wxeventskip}.
 105
 106 In practice, this would look like this if the derived text control only
 107 accepts 'a' to 'z' and 'A' to 'Z':
 108
 109 {\small%
 110 \begin{verbatim}
 111 void MyTextCtrl::OnChar(wxKeyEvent& event)
 112 {
 113     if ( isalpha( event.KeyCode() ) )
 114     {
 115        // key code is within legal range. we call event.Skip() so the
 116        // event can be processed either in the base wxWidgets class
 117        // or the native control.
 118
 119        event.Skip();
 120     }
 121     else
 122     {
 123        // illegal key hit. we don't call event.Skip() so the
 124        // event is not processed anywhere else.
 125
 126        wxBell();
 127     }
 128 }
 129 \end{verbatim}
 130 }%
 131
 132
 133 The normal order of event table searching by ProcessEvent is as follows:
 134
 135 \begin{enumerate}\itemsep=0pt
 136 \item If the object is disabled (via a call to \helpref{wxEvtHandler::SetEvtHandlerEnabled}{wxevthandlersetevthandlerenabled})
 137 the function skips to step (6).
 138 \item If the object is a wxWindow, {\bf ProcessEvent} is recursively called on the window's\rtfsp
 139 \helpref{wxValidator}{wxvalidator}. If this returns true, the function exits.
 140 \item {\bf SearchEventTable} is called for this event handler. If this fails, the base
 141 class table is tried, and so on until no more tables exist or an appropriate function was found,
 142 in which case the function exits.
 143 \item The search is applied down the entire chain of event handlers (usually the chain has a length
 144 of one). If this succeeds, the function exits.
 145 \item If the object is a wxWindow and the event is set to set to propagate (in the library only
 146 wxCommandEvent based events are set to propagate), {\bf ProcessEvent} is recursively applied
 147 to the parent window's event handler. If this returns true, the function exits.
 148 \item Finally, {\bf ProcessEvent} is called on the wxApp object.
 149 \end{enumerate}
 150
 151 {\bf Pay close attention to Step 5.}  People often overlook or get
 152 confused by this powerful feature of the wxWidgets event processing
 153 system.  To put it a different way, events set to propagate
 154 (\helpref{See: wxEvent::ShouldPropagate}{wxeventshouldpropagate})
 155 (most likely derived either directly or indirectly from wxCommandEvent)
 156 will travel up the containment hierarchy from child to parent until the
 157 maximal propagation level is reached or an event handler is found that
 158 doesn't call \helpref{event.Skip()}{wxeventskip}.
 159
 160 Finally, there is another additional complication (which, in fact, simplifies
 161 life of wxWidgets programmers significantly): when propagating the command
 162 events upwards to the parent window, the event propagation stops when it
 163 reaches the parent dialog, if any. This means that you don't risk to get
 164 unexpected events from the dialog controls (which might be left unprocessed by
 165 the dialog itself because it doesn't care about them) when a modal dialog is
 166 popped up. The events do propagate beyond the frames, however. The rationale
 167 for this choice is that there are only a few frames in a typical application
 168 and their parent-child relation are well understood by the programmer while it
 169 may be very difficult, if not impossible, to track down all the dialogs which
 170 may be popped up in a complex program (remember that some are created
 171 automatically by wxWidgets). If you need to specify a different behaviour for
 172 some reason, you can use
 173 \helpref{SetExtraStyle(wxWS\_EX\_BLOCK\_EVENTS)}{wxwindowsetextrastyle}
 174 explicitly to prevent the events from being propagated beyond the given window
 175 or unset this flag for the dialogs which have it on by default.
 176
 177 Typically events that deal with a window as a window (size, motion,
 178 paint, mouse, keyboard, etc.) are sent only to the window.  Events
 179 that have a higher level of meaning and/or are generated by the window
 180 itself, (button click, menu select, tree expand, etc.) are command
 181 events and are sent up to the parent to see if it is interested in the
 182 event.
 183
 184 Note that your application may wish to override ProcessEvent to redirect processing of
 185 events. This is done in the document/view framework, for example, to allow event handlers
 186 to be defined in the document or view. To test for command events (which will probably
 187 be the only events you wish to redirect), you may use
 188 \helpref{wxEvent::IsCommandEvent}{wxeventiscommandevent} for efficiency,
 189 instead of using the slower run-time type system.
 190
 191 As mentioned above, only command events are recursively applied to the parents event
 192 handler in the library itself. As this quite often causes confusion for users,
 193 here is a list of system events which will NOT get sent to the parent's event handler:
 194
 195 \begin{twocollist}\itemsep=0pt
 196 \twocolitem{\helpref{wxEvent}{wxevent}}{The event base class}
 197 \twocolitem{\helpref{wxActivateEvent}{wxactivateevent}}{A window or application activation event}
 198 \twocolitem{\helpref{wxCloseEvent}{wxcloseevent}}{A close window or end session event}
 199 \twocolitem{\helpref{wxEraseEvent}{wxeraseevent}}{An erase background event}
 200 \twocolitem{\helpref{wxFocusEvent}{wxfocusevent}}{A window focus event}
 201 \twocolitem{\helpref{wxKeyEvent}{wxkeyevent}}{A keypress event}
 202 \twocolitem{\helpref{wxIdleEvent}{wxidleevent}}{An idle event}
 203 \twocolitem{\helpref{wxInitDialogEvent}{wxinitdialogevent}}{A dialog initialisation event}
 204 \twocolitem{\helpref{wxJoystickEvent}{wxjoystickevent}}{A joystick event}
 205 \twocolitem{\helpref{wxMenuEvent}{wxmenuevent}}{A menu event}
 206 \twocolitem{\helpref{wxMouseEvent}{wxmouseevent}}{A mouse event}
 207 \twocolitem{\helpref{wxMoveEvent}{wxmoveevent}}{A move event}
 208 \twocolitem{\helpref{wxPaintEvent}{wxpaintevent}}{A paint event}
 209 \twocolitem{\helpref{wxQueryLayoutInfoEvent}{wxquerylayoutinfoevent}}{Used to query layout information}
 210 \twocolitem{\helpref{wxSetCursorEvent}{wxsetcursorevent}}{Used for special cursor processing based on current mouse position}
 211 \twocolitem{\helpref{wxSizeEvent}{wxsizeevent}}{A size event}
 212 \twocolitem{\helpref{wxScrollWinEvent}{wxscrollwinevent}}{A scroll event sent by a scrolled window (not a scroll bar)}
 213 \twocolitem{\helpref{wxSysColourChangedEvent}{wxsyscolourchangedevent}}{A system colour change event}
 214 \end{twocollist}
 215
 216 In some cases, it might be desired by the programmer to get a certain number
 217 of system events in a parent window, for example all key events sent to, but not
 218 used by, the native controls in a dialog. In this case, a special event handler
 219 will have to be written that will override ProcessEvent() in order to pass
 220 all events (or any selection of them) to the parent window.
 221
 222
 223 \subsection{Events generated by the user vs programmatically generated events}\label{progevent}
 224
 225 While generically \helpref{wxEvents}{wxevent} can be generated both by user
 226 actions (e.g. resize of a \helpref{wxWindow}{wxwindow}) and by calls to functions
 227 (e.g. \helpref{wxWindow::SetSize}{wxwindowsetsize}), wxWidgets controls
 228 normally send \helpref{wxCommandEvent}{wxcommandevent}-derived events only for
 229 the user-generated events. The only {\bf exceptions} to this rule are:
 230
 231 \begin{twocollist}\itemsep=0pt
 232 \twocolitem{\helpref{wxNotebook::AddPage}{wxnotebookaddpage}}{No event-free alternatives}
 233 \twocolitem{\helpref{wxNotebook::AdvanceSelection}{wxnotebookadvanceselection}}{No event-free alternatives}
 234 \twocolitem{\helpref{wxNotebook::DeletePage}{wxnotebookdeletepage}}{No event-free alternatives}
 235 \twocolitem{\helpref{wxNotebook::SetSelection}{wxnotebooksetselection}}{Use \helpref{wxNotebook::ChangeSelection}{wxnotebookchangeselection} instead, as \helpref{wxNotebook::SetSelection}{wxnotebooksetselection} is deprecated}
 236 \twocolitem{\helpref{wxTreeCtrl::Delete}{wxtreectrldelete}}{No event-free alternatives}
 237 \twocolitem{\helpref{wxTreeCtrl::DeleteAllItems}{wxtreectrldeleteallitems}}{No event-free alternatives}
 238 \twocolitem{\helpref{wxTreeCtrl::EditLabel}{wxtreectrleditlabel}}{No event-free alternatives}
 239 \twocolitem{All \helpref{wxTextCtrl}{wxtextctrl} methods}{\helpref{wxTextCtrl::ChangeValue}{wxtextctrlchangevalue} can be used instead
 240 of \helpref{wxTextCtrl::SetValue}{wxtextctrlsetvalue} but the other functions,
 241 such as \helpref{Replace}{wxtextctrlreplace} or \helpref{WriteText}{wxtextctrlwritetext}
 242 don't have event-free equivalents}
 243 \end{twocollist}
 244
 245
 246 % VZ: it doesn't work like this, but just in case we ever reenable this
 247 %     behaviour, I leave it here
 248 %
 249 % \subsection{Redirection of command events to the window with the focus}
 250 %
 251 % The usual upward search through the window hierarchy for command event
 252 % handlers does not always meet an application's requirements. Say you have two
 253 % wxTextCtrl windows in a frame, plus a toolbar with Cut, Copy and Paste
 254 % buttons. To avoid the need to define event handlers in the frame
 255 % and redirect them explicitly to the window with the focus, command events
 256 % are sent to the window with the focus first, for
 257 % menu and toolbar command and UI update events only. This means that
 258 % each window can handle its own commands and UI updates independently. In
 259 % fact wxTextCtrl can handle Cut, Copy, Paste, Undo and Redo commands and UI update
 260 % requests, so no extra coding is required to support them in your menus and
 261 % toolbars.
 262
 263 \subsection{Pluggable event handlers}\label{pluggablehandlers}
 264
 265 In fact, you don't have to derive a new class from a window class
 266 if you don't want to. You can derive a new class from wxEvtHandler instead,
 267 defining the appropriate event table, and then call
 268 \rtfsp\helpref{wxWindow::SetEventHandler}{wxwindowseteventhandler} (or, preferably,
 269 \rtfsp\helpref{wxWindow::PushEventHandler}{wxwindowpusheventhandler}) to make this
 270 event handler the object that responds to events. This way, you can avoid
 271 a lot of class derivation, and use the same event handler class (but different
 272 objects as the same event handler object shouldn't be used more than once) to
 273 handle events from instances of different classes. If you ever have to call a window's event handler
 274 manually, use the GetEventHandler function to retrieve the window's event handler and use that
 275 to call the member function. By default, GetEventHandler returns a pointer to the window itself
 276 unless an application has redirected event handling using SetEventHandler or PushEventHandler.
 277
 278 One use of PushEventHandler is to temporarily or permanently change the
 279 behaviour of the GUI. For example, you might want to invoke a dialog editor
 280 in your application that changes aspects of dialog boxes. You can
 281 grab all the input for an existing dialog box, and edit it `in situ',
 282 before restoring its behaviour to normal. So even if the application
 283 has derived new classes to customize behaviour, your utility can indulge
 284 in a spot of body-snatching. It could be a useful technique for on-line
 285 tutorials, too, where you take a user through a serious of steps and
 286 don't want them to diverge from the lesson. Here, you can examine the events
 287 coming from buttons and windows, and if acceptable, pass them through to
 288 the original event handler. Use PushEventHandler/PopEventHandler
 289 to form a chain of event handlers, where each handler processes a different
 290 range of events independently from the other handlers.
 291
 292 \subsection{Window identifiers}\label{windowids}
 293
 294 \index{identifiers}\index{wxID}Window identifiers are integers, and are used to
 295 uniquely determine window identity in the event system (though you can use it
 296 for other purposes). In fact, identifiers do not need to be unique
 297 across your entire application just so long as they are unique within a
 298 particular context you're interested in, such as a frame and its children. You
 299 may use the {\tt wxID\_OK} identifier, for example, on any number of dialogs so
 300 long as you don't have several within the same dialog.
 301
 302 If you pass {\tt wxID\_ANY} to a window constructor, an identifier will be
 303 generated for you automatically by wxWidgets. This is useful when you don't
 304 care about the exact identifier either because you're not going to process the
 305 events from the control being created at all or because you process the events
 306 from all controls in one place (in which case you should specify {\tt wxID\_ANY}
 307 in the event table or \helpref{wxEvtHandler::Connect}{wxevthandlerconnect} call
 308 as well. The automatically generated identifiers are always negative and so
 309 will never conflict with the user-specified identifiers which must be always
 310 positive.
 311
 312 The following standard identifiers are supplied. You can use wxID\_HIGHEST to
 313 determine the number above which it is safe to define your own identifiers. Or,
 314 you can use identifiers below wxID\_LOWEST.
 315
 316 \begin{verbatim}
 317 #define wxID_ANY                -1
 318
 319 #define wxID_LOWEST             4999
 320
 321 #define wxID_OPEN               5000
 322 #define wxID_CLOSE              5001
 323 #define wxID_NEW                5002
 324 #define wxID_SAVE               5003
 325 #define wxID_SAVEAS             5004
 326 #define wxID_REVERT             5005
 327 #define wxID_EXIT               5006
 328 #define wxID_UNDO               5007
 329 #define wxID_REDO               5008
 330 #define wxID_HELP               5009
 331 #define wxID_PRINT              5010
 332 #define wxID_PRINT_SETUP        5011
 333 #define wxID_PREVIEW            5012
 334 #define wxID_ABOUT              5013
 335 #define wxID_HELP_CONTENTS      5014
 336 #define wxID_HELP_COMMANDS      5015
 337 #define wxID_HELP_PROCEDURES    5016
 338 #define wxID_HELP_CONTEXT       5017
 339
 340 #define wxID_CUT                5030
 341 #define wxID_COPY               5031
 342 #define wxID_PASTE              5032
 343 #define wxID_CLEAR              5033
 344 #define wxID_FIND               5034
 345 #define wxID_DUPLICATE          5035
 346 #define wxID_SELECTALL          5036
 347 #define wxID_DELETE             5037
 348 #define wxID_REPLACE            5038
 349 #define wxID_REPLACE_ALL        5039
 350 #define wxID_PROPERTIES         5040
 351
 352 #define wxID_VIEW_DETAILS       5041
 353 #define wxID_VIEW_LARGEICONS    5042
 354 #define wxID_VIEW_SMALLICONS    5043
 355 #define wxID_VIEW_LIST          5044
 356 #define wxID_VIEW_SORTDATE      5045
 357 #define wxID_VIEW_SORTNAME      5046
 358 #define wxID_VIEW_SORTSIZE      5047
 359 #define wxID_VIEW_SORTTYPE      5048
 360
 361 #define wxID_FILE1              5050
 362 #define wxID_FILE2              5051
 363 #define wxID_FILE3              5052
 364 #define wxID_FILE4              5053
 365 #define wxID_FILE5              5054
 366 #define wxID_FILE6              5055
 367 #define wxID_FILE7              5056
 368 #define wxID_FILE8              5057
 369 #define wxID_FILE9              5058
 370
 371 #define wxID_OK                 5100
 372 #define wxID_CANCEL             5101
 373 #define wxID_APPLY              5102
 374 #define wxID_YES                5103
 375 #define wxID_NO                 5104
 376 #define wxID_STATIC             5105
 377
 378 #define wxID_HIGHEST            5999
 379 \end{verbatim}
 380
 381 \subsection{Event macros summary}\label{eventmacros}
 382
 383 \wxheading{Macros listed by event class}
 384
 385 The documentation for specific event macros is organised by event class. Please refer
 386 to these sections for details.
 387
 388 \twocolwidtha{8cm}%
 389 \begin{twocollist}\itemsep=0pt
 390 \twocolitem{\helpref{wxActivateEvent}{wxactivateevent}}{The EVT\_ACTIVATE and EVT\_ACTIVATE\_APP macros intercept
 391 activation and deactivation events.}
 392 \twocolitem{\helpref{wxCommandEvent}{wxcommandevent}}{A range of commonly-used control events.}
 393 \twocolitem{\helpref{wxCloseEvent}{wxcloseevent}}{The EVT\_CLOSE macro handles window closure
 394 called via \helpref{wxWindow::Close}{wxwindowclose}.}
 395 \twocolitem{\helpref{wxDropFilesEvent}{wxdropfilesevent}}{The EVT\_DROP\_FILES macros handles
 396 file drop events.}
 397 \twocolitem{\helpref{wxEraseEvent}{wxeraseevent}}{The EVT\_ERASE\_BACKGROUND macro is used to handle window erase requests.}
 398 \twocolitem{\helpref{wxFocusEvent}{wxfocusevent}}{The EVT\_SET\_FOCUS and EVT\_KILL\_FOCUS macros are used to handle keyboard focus events.}
 399 \twocolitem{\helpref{wxKeyEvent}{wxkeyevent}}{EVT\_CHAR, EVT\_KEY\_DOWN and
 400 EVT\_KEY\_UP macros handle keyboard input for any window.}
 401 \twocolitem{\helpref{wxIdleEvent}{wxidleevent}}{The EVT\_IDLE macro handle application idle events
 402 (to process background tasks, for example).}
 403 \twocolitem{\helpref{wxInitDialogEvent}{wxinitdialogevent}}{The EVT\_INIT\_DIALOG macro is used
 404 to handle dialog initialisation.}
 405 \twocolitem{\helpref{wxListEvent}{wxlistevent}}{These macros handle \helpref{wxListCtrl}{wxlistctrl} events.}
 406 \twocolitem{\helpref{wxMenuEvent}{wxmenuevent}}{These macros handle special menu events (not menu commands).}
 407 \twocolitem{\helpref{wxMouseEvent}{wxmouseevent}}{Mouse event macros can handle either individual
 408 mouse events or all mouse events.}
 409 \twocolitem{\helpref{wxMoveEvent}{wxmoveevent}}{The EVT\_MOVE macro is used to handle a window move.}
 410 \twocolitem{\helpref{wxPaintEvent}{wxpaintevent}}{The EVT\_PAINT macro is used to handle window paint requests.}
 411 \twocolitem{\helpref{wxScrollEvent}{wxscrollevent}}{These macros are used to handle scroll events from
 412 \helpref{wxScrollBar}{wxscrollbar}, \helpref{wxSlider}{wxslider},and \helpref{wxSpinButton}{wxspinbutton}.}
 413 \twocolitem{\helpref{wxSetCursorEvent}{wxsetcursorevent}}{The EVT\_SET\_CURSOR macro is used for special cursor processing.}
 414 \twocolitem{\helpref{wxSizeEvent}{wxsizeevent}}{The EVT\_SIZE macro is used to handle a window resize.}
 415 \twocolitem{\helpref{wxSplitterEvent}{wxsplitterevent}}{The EVT\_SPLITTER\_SASH\_POS\_CHANGED, EVT\_SPLITTER\_UNSPLIT
 416 and EVT\_SPLITTER\_DCLICK macros are used to handle the various splitter window events.}
 417 \twocolitem{\helpref{wxSysColourChangedEvent}{wxsyscolourchangedevent}}{The EVT\_SYS\_COLOUR\_CHANGED macro is used to handle
 418 events informing the application that the user has changed the system colours (Windows only).}
 419 \twocolitem{\helpref{wxTreeEvent}{wxtreeevent}}{These macros handle \helpref{wxTreeCtrl}{wxtreectrl} events.}
 420 \twocolitem{\helpref{wxUpdateUIEvent}{wxupdateuievent}}{The EVT\_UPDATE\_UI macro is used to handle user interface
 421 update pseudo-events, which are generated to give the application the chance to update the visual state of menus,
 422 toolbars and controls.}
 423 \end{twocollist}
 424
 425 \subsection{Custom event summary}\label{customevents}
 426
 427 \wxheading{General approach}
 428
 429 Since version 2.2.x of wxWidgets, each event type is identified by ID which
 430 is given to the event type {\it at runtime} which makes it possible to add
 431 new event types to the library or application without risking ID clashes
 432 (two different event types mistakingly getting the same event ID). This
 433 event type ID is stored in a struct of type {\bf const wxEventType}.
 434
 435 In order to define a new event type, there are principally two choices.
 436 One is to define a entirely new event class (typically deriving from
 437 \helpref{wxEvent}{wxevent} or \helpref{wxCommandEvent}{wxcommandevent}.
 438 The other is to use the existing event classes and give them an new event
 439 type. You'll have to define and declare a new event type using either way,
 440 and this is done using the following macros:
 441
 442 \begin{verbatim}
 443 // in the header of the source file
 444 BEGIN_DECLARE_EVENT_TYPES()
 445 DECLARE_EVENT_TYPE(name, value)
 446 END_DECLARE_EVENT_TYPES()
 447
 448 // in the implementation
 449 DEFINE_EVENT_TYPE(name)
 450 \end{verbatim}
 451
 452 You can ignore the {\it value} parameter of the DECLARE\_EVENT\_TYPE macro
 453 since it is used only for backwards compatibility with wxWidgets 2.0.x based
 454 applications where you have to give the event type ID an explicit value.
 455
 456 See also the \helpref{event sample}{sampleevent} for an example of code
 457 defining and working with the custom event types.
 458
 459 \wxheading{Using existing event classes}
 460
 461 If you just want to use a \helpref{wxCommandEvent}{wxcommandevent} with
 462 a new event type, you can then use one of the generic event table macros
 463 listed below, without having to define a new macro yourself. This also
 464 has the advantage that you won't have to define a new \helpref{wxEvent::Clone()}{wxeventclone}
 465 method for posting events between threads etc. This could look like this
 466 in your code:
 467
 468 {\small%
 469 \begin{verbatim}
 470 DECLARE_EVENT_TYPE(wxEVT_MY_EVENT, -1)
 471
 472 DEFINE_EVENT_TYPE(wxEVT_MY_EVENT)
 473
 474 // user code intercepting the event
 475
 476 BEGIN_EVENT_TABLE(MyFrame, wxFrame)
 477   EVT_MENU    (wxID_EXIT, MyFrame::OnExit)
 478   // ....
 479   EVT_COMMAND  (ID_MY_WINDOW, wxEVT_MY_EVENT, MyFrame::OnMyEvent)
 480 END_EVENT_TABLE()
 481
 482 void MyFrame::OnMyEvent( wxCommandEvent &event )
 483 {
 484     // do something
 485     wxString text = event.GetText();
 486 }
 487
 488
 489 // user code sending the event
 490
 491 void MyWindow::SendEvent()
 492 {
 493     wxCommandEvent event( wxEVT_MY_EVENT, GetId() );
 494     event.SetEventObject( this );
 495     // Give it some contents
 496     event.SetText( wxT("Hallo") );
 497     // Send it
 498     GetEventHandler()->ProcessEvent( event );
 499 }
 500 \end{verbatim}
 501 }%
 502
 503
 504 \wxheading{Generic event table macros}
 505
 506 \twocolwidtha{8cm}%
 507 \begin{twocollist}\itemsep=0pt
 508 \twocolitem{\windowstyle{EVT\_CUSTOM(event, id, func)}}{Allows you to add a custom event table
 509 entry by specifying the event identifier (such as wxEVT\_SIZE), the window identifier,
 510 and a member function to call.}
 511 \twocolitem{\windowstyle{EVT\_CUSTOM\_RANGE(event, id1, id2, func)}}{The same as EVT\_CUSTOM,
 512 but responds to a range of window identifiers.}
 513 \twocolitem{\windowstyle{EVT\_COMMAND(id, event, func)}}{The same as EVT\_CUSTOM, but
 514 expects a member function with a wxCommandEvent argument.}
 515 \twocolitem{\windowstyle{EVT\_COMMAND\_RANGE(id1, id2, event, func)}}{The same as EVT\_CUSTOM\_RANGE, but
 516 expects a member function with a wxCommandEvent argument.}
 517 \twocolitem{\windowstyle{EVT\_NOTIFY(event, id, func)}}{The same as EVT\_CUSTOM, but
 518 expects a member function with a wxNotifyEvent argument.}
 519 \twocolitem{\windowstyle{EVT\_NOTIFY\_RANGE(event, id1, id2, func)}}{The same as EVT\_CUSTOM\_RANGE, but
 520 expects a member function with a wxNotifyEvent argument.}
 521 \end{twocollist}
 522
 523
 524 \wxheading{Defining your own event class}
 525
 526 Under certain circumstances, it will be required to define your own event
 527 class e.g. for sending more complex data from one place to another. Apart
 528 from defining your event class, you will also need to define your own
 529 event table macro (which is quite long). Watch out to put in enough
 530 casts to the inherited event function. Here is an example, taken mostly
 531 from the {\it wxPlot} library, which is in the {\it contrib} section of
 532 the wxWidgets sources.
 533
 534 {\small%
 535 \begin{verbatim}
 536
 537 // code defining event
 538
 539 class wxPlotEvent: public wxNotifyEvent
 540 {
 541 public:
 542     wxPlotEvent( wxEventType commandType = wxEVT_NULL, int id = 0 );
 543
 544     // accessors
 545     wxPlotCurve *GetCurve()
 546         { return m_curve; }
 547
 548     // required for sending with wxPostEvent()
 549     wxEvent* Clone();
 550
 551 private:
 552     wxPlotCurve   *m_curve;
 553 };
 554
 555 DECLARE_EVENT_MACRO( wxEVT_PLOT_ACTION, -1 )
 556
 557 typedef void (wxEvtHandler::*wxPlotEventFunction)(wxPlotEvent&);
 558
 559 #define EVT_PLOT(id, fn) \
 560     DECLARE_EVENT_TABLE_ENTRY( wxEVT_PLOT_ACTION, id, -1, \
 561     (wxObjectEventFunction) (wxEventFunction) (wxCommandEventFunction) (wxNotifyEventFunction) \
 562     wxStaticCastEvent( wxPlotEventFunction, & fn ), (wxObject *) NULL ),
 563
 564
 565 // code implementing the event type and the event class
 566
 567 DEFINE_EVENT_TYPE( wxEVT_PLOT_ACTION )
 568
 569 wxPlotEvent::wxPlotEvent( ...
 570
 571
 572 // user code intercepting the event
 573
 574 BEGIN_EVENT_TABLE(MyFrame, wxFrame)
 575   EVT_PLOT  (ID_MY_WINDOW,  MyFrame::OnPlot)
 576 END_EVENT_TABLE()
 577
 578 void MyFrame::OnPlot( wxPlotEvent &event )
 579 {
 580     wxPlotCurve *curve = event.GetCurve();
 581 }
 582
 583
 584 // user code sending the event
 585
 586 void MyWindow::SendEvent()
 587 {
 588     wxPlotEvent event( wxEVT_PLOT_ACTION, GetId() );
 589     event.SetEventObject( this );
 590     event.SetCurve( m_curve );
 591     GetEventHandler()->ProcessEvent( event );
 592 }
 593
 594 \end{verbatim}
 595 }%
 596