-/////////////////////////////////////////////////////////////////////////////\r
-// Name: eventhandling.h\r
-// Purpose: topic overview\r
-// Author: wxWidgets team\r
-// RCS-ID: $Id$\r
-// Licence: wxWindows license\r
-/////////////////////////////////////////////////////////////////////////////\r
-\r
-/**\r
-\r
-@page overview_eventhandling Event Handling\r
-\r
-Classes: wxEvtHandler, wxWindow, wxEvent\r
-\r
-@li @ref overview_eventhandling_introduction\r
-@li @ref overview_eventhandling_eventtables\r
-@li @ref overview_eventhandling_connect\r
-@li @ref overview_eventhandling_processing\r
-@li @ref overview_eventhandling_propagation\r
-@li @ref overview_eventhandling_virtual\r
-@li @ref overview_eventhandling_prog\r
-@li @ref overview_eventhandling_pluggable\r
-@li @ref overview_eventhandling_winid\r
-@li @ref overview_eventhandling_custom\r
-@li @ref overview_eventhandling_macros\r
-\r
-\r
-<hr>\r
-\r
-\r
-@section overview_eventhandling_introduction Introduction\r
-\r
-There are two principal ways to handle events in wxWidgets. One of them uses\r
-<em>event table</em> macros and allows you to define the connection between events\r
-and their handlers only statically, i.e. during program compilation. The other\r
-one uses wxEvtHandler::Connect() call and can be used to connect, and\r
-disconnect, the handlers dynamically, i.e. during run-time depending on some\r
-conditions. It also allows directly connecting the events of one object to a\r
-handler method in another object while the static event tables can only handle\r
-events in the object where they are defined so using Connect() is more flexible\r
-than using the event tables. On the other hand, event tables are more succinct\r
-and centralize all event handlers connection in one place. You can either\r
-choose a single approach which you find preferable or freely combine both\r
-methods in your program in different classes or even in one and the same class,\r
-although this is probably sufficiently confusing to be a bad idea.\r
-\r
-But before you make this choice, let us discuss these two ways in some more\r
-details: in the next section we provide a short introduction to handling the\r
-events using the event tables, please see @ref overview_eventhandling_connect\r
-for the discussion of Connect().\r
-\r
-@section overview_eventhandling_eventtables Event Handling with Event Tables\r
-\r
-To use an <em>event table</em> you must first decide in which class you wish to\r
-handle the events. The only requirement imposed by wxWidgets is that this class\r
-must derive from wxEvtHandler and so, considering that wxWindow derives from\r
-it, any classes representing windows can handle events. Simple events such as\r
-menu commands are usually processed at the level of a top-level window\r
-containing the menu, so let's suppose that you need to handle some events in @c\r
-MyFrame class deriving from wxFrame.\r
-\r
-First thing to do is to define one or more <em>event handlers</em>. They\r
-are just simple (non-virtual) methods of the class which take as a parameter a\r
-reference to an object of wxEvent-derived class and have no return value (any\r
-return information is passed via the argument, which is why it is non-const).\r
-You also need to insert a macro\r
-\r
-@code\r
-DECLARE_EVENT_TABLE()\r
-@endcode\r
-\r
-somewhere in the class declaration. It doesn't matter where does it occur but\r
-it's customary to put it at the end of it because the macro changes the access\r
-type internally and so it's safest if there is nothing that follows it. So the\r
-full class declaration might look like this:\r
-\r
-@code\r
-class MyFrame : public wxFrame\r
-{\r
-public:\r
- MyFrame(...) : wxFrame(...) { }\r
-\r
- ...\r
-\r
-protected:\r
- int m_whatever;\r
-\r
-private:\r
- // notice that as the event handlers normally are not called from outside\r
- // the class, they normally be private, in particular they don't need at\r
- // all to be public\r
- void OnExit(wxCommandEvent& event);\r
- void OnButton1(wxCommandEvent& event);\r
- void OnSize(wxSizeEvent& event);\r
-\r
- // it's common to call the event handlers OnSomething() but there is no\r
- // obligation to it, this one is an event handler too:\r
- void DoTest(wxCommandEvent& event);\r
-\r
- DECLARE_EVENT_TABLE()\r
-};\r
-@endcode\r
-\r
-Next the event table must be defined and, as any definition, it must be placed\r
-in an implementation file to tell. The event table tells wxWidgets how to map\r
-events to member functions and in our example it could look like this:\r
-\r
-@code\r
-BEGIN_EVENT_TABLE(MyFrame, wxFrame)\r
- EVT_MENU(wxID_EXIT, MyFrame::OnExit)\r
- EVT_MENU(DO_TEST, MyFrame::DoTest)\r
- EVT_SIZE(MyFrame::OnSize)\r
- EVT_BUTTON(BUTTON1, MyFrame::OnButton1)\r
-END_EVENT_TABLE()\r
-@endcode\r
-\r
-Notice that you must mention a method you want to use for the event handling in\r
-the event table definition, just defining it in MyFrame class is @e not enough.\r
-\r
-Let us now look at the details of this definition: the first line means that we\r
-are defining the event table for MyFrame class and that its base class is\r
-wxFrame, so events not processed by MyFrame will, by default, be handled to\r
-wxFrame. The next four lines define connections of individual events to their\r
-handlers: the first two of them map menu commands from the items with the\r
-identifiers specified as the first macro parameter to two different member\r
-functions. In the next one, @c EVT_SIZE means that any changes in the size of\r
-the frame will result in calling OnSize() method. Note that this macro doesn't\r
-need a window identifier, since normally you are only interested in the current\r
-window's size events.\r
-\r
-The EVT_BUTTON macro demonstrates that the originating event does not have to\r
-come from the window class implementing the event table -- if the event source\r
-is a button within a panel within a frame, this will still work, because event\r
-tables are searched up through the hierarchy of windows for the command events\r
-(but only command events, so you can't catch mouse move events in a child\r
-control in the parent window in the same way because wxMouseEvent doesn't\r
-derive from wxCommandEvent, see below for how you can do it). In this case, the\r
-button's event table will be searched, then the parent panel's, then the\r
-frame's.\r
-\r
-Finally, you need to implement the event handlers. As mentioned before, all\r
-event handlers take a wxEvent-derived argument whose exact class differs\r
-according to the type of event and the class of the originating window. For\r
-size events, wxSizeEvent is used. For menu commands and most control commands\r
-(such as button presses), wxCommandEvent is used. And when controls get more\r
-complicated, more specific wxCommandEvent-derived event classes providing\r
-additional control-specific information can be used, such as wxTreeEvent for\r
-events from wxTreeCtrl windows.\r
-\r
-In the simplest possible case an event handler may not use the @c event\r
-parameter at all, e.g.\r
-\r
-@code\r
-void MyFrame::OnExit(wxCommandEvent&)\r
-{\r
- // when the user selects "Exit" from the menu we should close\r
- Close(true);\r
-}\r
-@endcode\r
-\r
-In other cases you may need some information carried by the @c event argument,\r
-as in:\r
-\r
-@code\r
-void MyFrame::OnSize(wxSizeEvent& event)\r
-{\r
- wxSize size = event.GetSize();\r
-\r
- ... update the frame using the new size ...\r
-}\r
-@endcode\r
-\r
-You will find the details about the event table macros and the corresponding\r
-wxEvent-derived classes in the discussion of each control generating these\r
-events.\r
-\r
-\r
-@section overview_eventhandling_connect Dynamic Event Handling\r
-\r
-As with the event tables, you need to decide in which class do you intend to\r
-handle the events first and, also as before, this class must still derive from\r
-wxEvtHandler (usually indirectly via wxWindow), see the declaration of MyFrame\r
-in the previous section. However the similarities end here and both the syntax\r
-and the possibilities of this way of handling events in this way are rather\r
-different.\r
-\r
-Let us start by looking at the syntax: the first obvious difference is that you\r
-don't need to use neither @c DECLARE_EVENT_TABLE() nor @c BEGIN_EVENT_TABLE and\r
-associated macros any more. Instead, in any place in your code, but usually in\r
-the code of the class defining the handlers itself (and definitely not in the\r
-global scope as with the event tables), you should call its Connect() method\r
-like this:\r
-\r
-@code\r
-MyFrame::MyFrame(...)\r
-{\r
- Connect(wxID_EXIT, wxEVT_COMMAND_MENU_SELECTED,\r
- wxCommandEventHandler(MyFrame::OnExit));\r
-}\r
-@endcode\r
-\r
-This class should be self-explanatory except for wxCommandEventHandler part:\r
-this is a macro which ensures that the method is of correct type by using\r
-static_cast in the same way as event table macros do it inside them.\r
-\r
-Now let us describe the semantic differences:\r
-<ul>\r
- <li>\r
- Event handlers can be connected at any moment, e.g. it's possible to do\r
- some initialization first and only connect the handlers if and when it\r
- succeeds. This can avoid the need to test that the object was properly\r
- initialized in the event handlers themselves: with Connect() they\r
- simply won't be called at all if it wasn't.\r
- </li>\r
-\r
- <li>\r
- As a slight extension of the above, the handlers can also be\r
- Disconnect()-ed at any time. And maybe later reconnected again. Of\r
- course, it's also possible to emulate this behaviour with the classic\r
- static (i.e. connected via event tables) handlers by using an internal\r
- flag indicating whether the handler is currently enabled and returning\r
- from it if it isn't, but using dynamically connected handlers requires\r
- less code and is also usually more clear.\r
- </li>\r
-\r
- <li>\r
- Also notice that you must derive a class inherited from, say,\r
- wxTextCtrl even if you don't want to modify the control behaviour at\r
- all but just want to handle some of its events. This is especially\r
- inconvenient when the control is loaded from the XRC. Connecting the\r
- event handler dynamically bypasses the need for this unwanted\r
- sub-classing.\r
- </li>\r
-\r
- <li>\r
- Last but very, very far from least is the possibility to connect an\r
- event of some object to a method of another object. This is impossible\r
- to do with event tables because there is no possibility to specify the\r
- object to dispatch the event to so it necessarily needs to be sent to\r
- the same object which generated the event. Not so with Connect() which\r
- has an optional @c eventSink parameter which can be used to specify the\r
- object which will handle the event. Of course, in this case the method\r
- being connected must belong to the class which is the type of the\r
- @c eventSink object! To give a quick example, people often want to catch\r
- mouse movement events happening when the mouse is in one of the frame\r
- children in the frame itself. Doing it in a naive way doesn't work:\r
- <ul>\r
- <li>\r
- A @c EVT_LEAVE_WINDOW(MyFrame::OnMouseLeave) line in the frame\r
- event table has no effect as mouse move (including entering and\r
- leaving) events are not propagated upwards to the parent window\r
- (at least not by default).\r
- </li>\r
-\r
- <li>\r
- Putting the same line in a child event table will crash during\r
- run-time because the MyFrame method will be called on a wrong\r
- object -- it's easy to convince oneself that the only object\r
- which can be used here is the pointer to the child, as\r
- wxWidgets has nothing else. But calling a frame method with the\r
- child window pointer instead of the pointer to the frame is, of\r
- course, disastrous.\r
- </li>\r
- </ul>\r
-\r
- However writing\r
- @code\r
- MyFrame::MyFrame(...)\r
- {\r
- m_child->Connect(wxID_ANY, wxEVT_LEAVE_WINDOW,\r
- wxMouseEventHandler(MyFrame::OnMouseLeave),\r
- NULL, // unused extra data parameter\r
- this); // this indicates the object to connect to\r
- }\r
- @endcode\r
- will work exactly as expected. Note that you can get the object which\r
- generated the event -- and which is not the same as the frame -- via\r
- wxEvent::GetEventObject() method of @c event argument passed to the\r
- event handler.\r
- </li>\r
-</ul>\r
-\r
-To summarize, using Connect() requires slightly more typing but is much more\r
-flexible than using static event tables so don't hesitate to use it when you\r
-need this extra power. On the other hand, event tables are still perfectly fine\r
-in simple situations where this extra flexibility is not needed.\r
-\r
-\r
-@section overview_eventhandling_processing How Events are Processed\r
-\r
-The previous sections explain how to define event handlers but don't address\r
-the question of how exactly does wxWidgets find the handler to call for the\r
-given event. This section describes the algorithm used to do it in details.\r
-\r
-When an event is received from the windowing system, wxWidgets calls\r
-wxEvtHandler::ProcessEvent() on the first event handler object belonging to the\r
-window generating the event. The normal order of event table searching by\r
-ProcessEvent() is as follows, with the event processing stopping as soon as a\r
-handler is found (unless the handler calls wxEvent::Skip() in which case it\r
-doesn't count as having handled the event and the search continues):\r
-<ol>\r
- <li value="0">\r
- Before anything else happens, wxApp::FilterEvent() is called. If it returns\r
- anything but -1 (default), the event handling stops immediately.\r
- </li>\r
-\r
- <li value="1">\r
- If this event handler is disabled via a call to\r
- wxEvtHandler::SetEvtHandlerEnabled() the next three steps are skipped and\r
- the event handler resumes at step (5).\r
- </li?\r
-\r
- <li value="2">\r
- If the object is a wxWindow and has an associated validator, wxValidator\r
- gets a chance to process the event.\r
- </li>\r
-\r
- <li value="3">\r
- The list of dynamically connected event handlers, i.e. those for which\r
- Connect() was called, is consulted. Notice that this is done before\r
- checking the static event table entries, so if both a dynamic and a static\r
- event handler match the same event, the static one is never going to be\r
- used.\r
- </li>\r
-\r
- <li value="4">\r
- The event table containing all the handlers defined using the event table\r
- macros in this class and its base classes is examined. Notice that this\r
- means that any event handler defined in a base class will be executed at\r
- this step.\r
- </li>\r
-\r
- <li value="5">\r
- The event is passed to the next event handler, if any, in the event handler\r
- chain, i.e. the steps (1) to (4) are done for it. This chain can be formed\r
- using wxEvtHandler::SetNextHandler() or wxWindow::PushEventHandler() but\r
- usually there is no next event handler and chaining event handlers using\r
- these functions is much less useful now that Connect() exists so this step\r
- will almost never do anything.\r
- </li>\r
-\r
- <li value="6">\r
- If the object is a wxWindow and the event is set to propagate (by default\r
- only wxCommandEvent-derived events are set to propagate), then the\r
- processing restarts from the step (1) (and excluding the step (7)) for the\r
- parent window. If this object is not a window but the next handler exists,\r
- the event is passed to its parent if it is a window. This ensures that in a\r
- common case of (possibly several) non-window event handlers pushed on top\r
- of a window, the event eventually reaches the window parent.\r
- </li>\r
-\r
- <li value="7">\r
- Finally, i.e. if the event is still not processed, the wxApp object itself\r
- gets a last chance to process it.\r
- </li>\r
-</ol>\r
-\r
-<em>Please pay close attention to step 6!</em> People often overlook or get\r
-confused by this powerful feature of the wxWidgets event processing system. The\r
-details of event propagation upwards the window hierarchy are described in the\r
-next section.\r
-\r
-Also please notice that there are additional steps in the event handling for\r
-the windows making part of wxWidgets document-view framework, i.e.\r
-wxDocParentFrame, wxDocChildFrame and their MDI equivalents wxDocMDIParentFrame\r
-and wxDocMDIChildFrame. The parent frame classes modify the step (2) above to\r
-send the events received by them to wxDocManager object first. This object, in\r
-turn, sends the event to the current view and the view itself lets its\r
-associated document to process the event first. The child frame classes send\r
-the event directly to the associated view which still forwards it to its\r
-document object. Notice that to avoid remembering the exact order in which the\r
-events are processed in the document-view frame, the simplest, and recommended,\r
-solution is to only handle the events at the view classes level, but not in the\r
-document or document manager classes\r
-\r
-\r
-@section overview_eventhandling_propagation How Events Propagate Upwards\r
-\r
-As mentioned in the previous section, the events of the classes deriving from\r
-wxCommandEvent are propagated by default to the parent window if they are not\r
-processed in this window itself. But although by default only the command\r
-events are propagated like this, other events can be propagated as well because\r
-the event handling code uses wxEvent::ShouldPropagate() to check for whether an\r
-event should be propagated. It is also possible to propagate the event only a\r
-limited number of times and not until it is processed (or a top level parent\r
-window is reached).\r
-\r
-Finally, there is another additional complication (which, in fact, simplifies\r
-life of wxWidgets programmers significantly): when propagating the command\r
-events upwards to the parent window, the event propagation stops when it\r
-reaches the parent dialog, if any. This means that you don't risk to get\r
-unexpected events from the dialog controls (which might be left unprocessed by\r
-the dialog itself because it doesn't care about them) when a modal dialog is\r
-popped up. The events do propagate beyond the frames, however. The rationale\r
-for this choice is that there are only a few frames in a typical application\r
-and their parent-child relation are well understood by the programmer while it\r
-may be very difficult, if not impossible, to track down all the dialogs which\r
-may be popped up in a complex program (remember that some are created\r
-automatically by wxWidgets). If you need to specify a different behaviour for\r
-some reason, you can use wxWindow::SetExtraStyle(wxWS_EX_BLOCK_EVENTS)\r
-explicitly to prevent the events from being propagated beyond the given window\r
-or unset this flag for the dialogs which have it on by default.\r
-\r
-Typically events that deal with a window as a window (size, motion,\r
-paint, mouse, keyboard, etc.) are sent only to the window. Events\r
-that have a higher level of meaning and/or are generated by the window\r
-itself, (button click, menu select, tree expand, etc.) are command\r
-events and are sent up to the parent to see if it is interested in the event.\r
-\r
-As mentioned above, only command events are recursively applied to the parents\r
-event handler in the library itself. As this quite often causes confusion for\r
-users, here is a list of system events which will @em not get sent to the\r
-parent's event handler:\r
-\r
-@li wxEvent: The event base class\r
-@li wxActivateEvent: A window or application activation event\r
-@li wxCloseEvent: A close window or end session event\r
-@li wxEraseEvent: An erase background event\r
-@li wxFocusEvent: A window focus event\r
-@li wxKeyEvent: A keypress event\r
-@li wxIdleEvent: An idle event\r
-@li wxInitDialogEvent: A dialog initialisation event\r
-@li wxJoystickEvent: A joystick event\r
-@li wxMenuEvent: A menu event\r
-@li wxMouseEvent: A mouse event\r
-@li wxMoveEvent: A move event\r
-@li wxPaintEvent: A paint event\r
-@li wxQueryLayoutInfoEvent: Used to query layout information\r
-@li wxSetCursorEvent: Used for special cursor processing based on current mouse position\r
-@li wxSizeEvent: A size event\r
-@li wxScrollWinEvent: A scroll event sent by a scrolled window (not a scroll bar)\r
-@li wxSysColourChangedEvent: A system colour change event\r
-\r
-In some cases, it might be desired by the programmer to get a certain number\r
-of system events in a parent window, for example all key events sent to, but not\r
-used by, the native controls in a dialog. In this case, a special event handler\r
-will have to be written that will override ProcessEvent() in order to pass\r
-all events (or any selection of them) to the parent window.\r
-\r
-\r
-@section overview_eventhandling_virtual Event Handlers vs Virtual Methods\r
-\r
-It may be noted that wxWidgets' event processing system implements something\r
-close to virtual methods in normal C++ in spirit: both of these mechanisms\r
-allow to alter the behaviour of the base class by defining the event handling\r
-functions in the derived classes.\r
-\r
-There is however an important difference between the two mechanisms when you\r
-want to invoke the default behaviour, as implemented by the base class, from a\r
-derived class handler. With the virtual functions, you need to call the base\r
-class function directly and you can do it either in the beginning of the\r
-derived class handler function (to post-process the event) or at its end (to\r
-pre-process the event). With the event handlers, you only have the option of\r
-pre-processing the events and in order to still let the default behaviour to\r
-happen you must call wxEvent::Skip() and @em not call the base class event\r
-handler directly. In fact, the event handler probably doesn't even exist in the\r
-base class as the default behaviour is often implemented in platform-specific\r
-code by the underlying toolkit or OS itself. But even if it does exist at\r
-wxWidgets level, it should never be called directly as the event handler are\r
-not part of wxWidgets API and should never be called directly.\r
-\r
-Finally, please notice that the event handlers themselves shouldn't be virtual.\r
-They should always be non-virtual and usually private (as there is no need to\r
-make them public) methods of a wxEvtHandler-derived class.\r
-\r
-\r
-@section overview_eventhandling_prog User Generated Events vs Programmatically Generated Events\r
-\r
-While generically wxEvents can be generated both by user\r
-actions (e.g. resize of a wxWindow) and by calls to functions\r
-(e.g. wxWindow::SetSize), wxWidgets controls normally send wxCommandEvent-derived\r
-events only for the user-generated events. The only @b exceptions to this rule are:\r
-\r
-@li wxNotebook::AddPage: No event-free alternatives\r
-@li wxNotebook::AdvanceSelection: No event-free alternatives\r
-@li wxNotebook::DeletePage: No event-free alternatives\r
-@li wxNotebook::SetSelection: Use wxNotebook::ChangeSelection instead, as\r
- wxNotebook::SetSelection is deprecated\r
-@li wxTreeCtrl::Delete: No event-free alternatives\r
-@li wxTreeCtrl::DeleteAllItems: No event-free alternatives\r
-@li wxTreeCtrl::EditLabel: No event-free alternatives\r
-@li All wxTextCtrl methods\r
-\r
-wxTextCtrl::ChangeValue can be used instead of wxTextCtrl::SetValue but the other\r
-functions, such as wxTextCtrl::Replace or wxTextCtrl::WriteText don't have event-free\r
-equivalents.\r
-\r
-\r
-\r
-@section overview_eventhandling_pluggable Pluggable Event Handlers\r
-\r
-In fact, you don't have to derive a new class from a window class\r
-if you don't want to. You can derive a new class from wxEvtHandler instead,\r
-defining the appropriate event table, and then call wxWindow::SetEventHandler\r
-(or, preferably, wxWindow::PushEventHandler) to make this\r
-event handler the object that responds to events. This way, you can avoid\r
-a lot of class derivation, and use instances of the same event handler class (but different\r
-objects as the same event handler object shouldn't be used more than once) to\r
-handle events from instances of different widget classes.\r
-\r
-If you ever have to call a window's event handler\r
-manually, use the GetEventHandler function to retrieve the window's event handler and use that\r
-to call the member function. By default, GetEventHandler returns a pointer to the window itself\r
-unless an application has redirected event handling using SetEventHandler or PushEventHandler.\r
-\r
-One use of PushEventHandler is to temporarily or permanently change the\r
-behaviour of the GUI. For example, you might want to invoke a dialog editor\r
-in your application that changes aspects of dialog boxes. You can\r
-grab all the input for an existing dialog box, and edit it 'in situ',\r
-before restoring its behaviour to normal. So even if the application\r
-has derived new classes to customize behaviour, your utility can indulge\r
-in a spot of body-snatching. It could be a useful technique for on-line\r
-tutorials, too, where you take a user through a serious of steps and\r
-don't want them to diverge from the lesson. Here, you can examine the events\r
-coming from buttons and windows, and if acceptable, pass them through to\r
-the original event handler. Use PushEventHandler/PopEventHandler\r
-to form a chain of event handlers, where each handler processes a different\r
-range of events independently from the other handlers.\r
-\r
-\r
-\r
-@section overview_eventhandling_winid Window Identifiers\r
-\r
-Window identifiers are integers, and are used to\r
-uniquely determine window identity in the event system (though you can use it\r
-for other purposes). In fact, identifiers do not need to be unique\r
-across your entire application just so long as they are unique within a\r
-particular context you're interested in, such as a frame and its children. You\r
-may use the @c wxID_OK identifier, for example, on any number of dialogs so\r
-long as you don't have several within the same dialog.\r
-\r
-If you pass @c wxID_ANY to a window constructor, an identifier will be\r
-generated for you automatically by wxWidgets. This is useful when you don't\r
-care about the exact identifier either because you're not going to process the\r
-events from the control being created at all or because you process the events\r
-from all controls in one place (in which case you should specify @c wxID_ANY\r
-in the event table or wxEvtHandler::Connect call\r
-as well. The automatically generated identifiers are always negative and so\r
-will never conflict with the user-specified identifiers which must be always\r
-positive.\r
-\r
-See @ref page_stdevtid for the list of standard identifiers available.\r
-You can use wxID_HIGHEST to determine the number above which it is safe to\r
-define your own identifiers. Or, you can use identifiers below wxID_LOWEST.\r
-Finally, you can allocate identifiers dynamically using wxNewId() function to.\r
-If you use wxNewId() consistently in your application, you can be sure that\r
-the your identifiers don't conflict accidentally.\r
-\r
-\r
-@section overview_eventhandling_custom Custom Event Summary\r
-\r
-@subsection overview_eventhandling_custom_general General approach\r
-\r
-Since version 2.2.x of wxWidgets, each event type is identified by ID which\r
-is given to the event type @e at runtime which makes it possible to add\r
-new event types to the library or application without risking ID clashes\r
-(two different event types mistakingly getting the same event ID).\r
-This event type ID is stored in a struct of type <b>const wxEventType</b>.\r
-\r
-In order to define a new event type, there are principally two choices.\r
-One is to define a entirely new event class (typically deriving from\r
-wxEvent or wxCommandEvent).\r
-\r
-The other is to use the existing event classes and give them an new event\r
-type. You'll have to define and declare a new event type using either way,\r
-and this is done using the following macros:\r
-\r
-@code\r
-// in the header of the source file\r
-extern const wxEventType wxEVT_YOUR_EVENT_NAME;\r
-\r
-// in the implementation\r
-DEFINE_EVENT_TYPE(wxEVT_YOUR_EVENT_NAME)\r
-@endcode\r
-\r
-See also the @ref page_samples_event for an example of code\r
-defining and working with the custom event types.\r
-\r
-\r
-@subsection overview_eventhandling_custom_existing Using Existing Event Classes\r
-\r
-If you just want to use a wxCommandEvent with a new event type, you can then use\r
-one of the generic event table macros listed below, without having to define a\r
-new event class yourself. This also has the advantage that you won't have to define a\r
-new wxEvent::Clone() method for posting events between threads etc.\r
-\r
-Example:\r
-\r
-@code\r
-extern const wxEventType wxEVT_MY_EVENT;\r
-DEFINE_EVENT_TYPE(wxEVT_MY_EVENT)\r
-\r
-// user code intercepting the event\r
-\r
-BEGIN_EVENT_TABLE(MyFrame, wxFrame)\r
-EVT_MENU (wxID_EXIT, MyFrame::OnExit)\r
-// ....\r
-EVT_COMMAND (ID_MY_WINDOW, wxEVT_MY_EVENT, MyFrame::OnMyEvent)\r
-END_EVENT_TABLE()\r
-\r
-void MyFrame::OnMyEvent( wxCommandEvent& event )\r
-{\r
- // do something\r
- wxString text = event.GetText();\r
-}\r
-\r
-\r
-// user code sending the event\r
-\r
-void MyWindow::SendEvent()\r
-{\r
- wxCommandEvent event( wxEVT_MY_EVENT, GetId() );\r
- event.SetEventObject( this );\r
-\r
- // Give it some contents\r
- event.SetText( wxT("Hallo") );\r
-\r
- // Send it\r
- GetEventHandler()->ProcessEvent( event );\r
-}\r
-@endcode\r
-\r
-\r
-@subsection overview_eventhandling_custom_generic Generic Event Table Macros\r
-\r
-@beginTable\r
-@row2col{EVT_CUSTOM(event\, id\, func),\r
- Allows you to add a custom event table\r
- entry by specifying the event identifier (such as wxEVT_SIZE),\r
- the window identifier, and a member function to call.}\r
-@row2col{EVT_CUSTOM_RANGE(event\, id1\, id2\, func),\r
- The same as EVT_CUSTOM, but responds to a range of window identifiers.}\r
-@row2col{EVT_COMMAND(id\, event\, func),\r
- The same as EVT_CUSTOM, but expects a member function with a\r
- wxCommandEvent argument.}\r
-@row2col{EVT_COMMAND_RANGE(id1\, id2\, event\, func),\r
- The same as EVT_CUSTOM_RANGE, but\r
- expects a member function with a wxCommandEvent argument.}\r
-@row2col{EVT_NOTIFY(event\, id\, func),\r
- The same as EVT_CUSTOM, but\r
- expects a member function with a wxNotifyEvent argument.}\r
-@row2col{EVT_NOTIFY_RANGE(event\, id1\, id2\, func),\r
- The same as EVT_CUSTOM_RANGE, but\r
- expects a member function with a wxNotifyEvent argument.}\r
-@endTable\r
-\r
-\r
-@subsection overview_eventhandling_custom_ownclass Defining Your Own Event Class\r
-\r
-Under certain circumstances, it will be required to define your own event\r
-class e.g. for sending more complex data from one place to another. Apart\r
-from defining your event class, you will also need to define your own\r
-event table macro (which is quite long). Watch out to put in enough\r
-casts to the inherited event function. Here is an example:\r
-\r
-@code\r
-// code defining event\r
-\r
-class wxPlotEvent: public wxNotifyEvent\r
-{\r
-public:\r
- wxPlotEvent( wxEventType commandType = wxEVT_NULL, int id = 0 );\r
-\r
- // accessors\r
- wxPlotCurve *GetCurve()\r
- { return m_curve; }\r
-\r
- // required for sending with wxPostEvent()\r
- virtual wxEvent *Clone() const;\r
-\r
-private:\r
- wxPlotCurve *m_curve;\r
-};\r
-\r
-extern const wxEventType wxEVT_PLOT_ACTION;\r
-typedef void (wxEvtHandler::*wxPlotEventFunction)(wxPlotEvent&);\r
-\r
-#define wxPlotEventHandler(func) \\r
- (wxObjectEventFunction)(wxEventFunction)wxStaticCastEvent(wxPlotEventFunction, &func)\r
-#define EVT_PLOT(id, fn) \\r
- wx__DECLARE_EVT1(wxEVT_PLOT_ACTION, id, wxPlotEventHandler(fn))\r
-\r
-\r
-// code implementing the event type and the event class\r
-\r
-DEFINE_EVENT_TYPE( wxEVT_PLOT_ACTION )\r
-\r
-wxPlotEvent::wxPlotEvent( ... )\r
-{\r
- ...\r
-}\r
-\r
-\r
-// user code intercepting the event\r
-\r
-BEGIN_EVENT_TABLE(MyFrame, wxFrame)\r
-EVT_PLOT (ID_MY_WINDOW, MyFrame::OnPlot)\r
-END_EVENT_TABLE()\r
-\r
-void MyFrame::OnPlot( wxPlotEvent &event )\r
-{\r
- wxPlotCurve *curve = event.GetCurve();\r
-}\r
-\r
-\r
-// user code sending the event\r
-\r
-void MyWindow::SendEvent()\r
-{\r
- wxPlotEvent event( wxEVT_PLOT_ACTION, GetId() );\r
- event.SetEventObject( this );\r
- event.SetCurve( m_curve );\r
- GetEventHandler()->ProcessEvent( event );\r
-}\r
-@endcode\r
-\r
-\r
-@section overview_eventhandling_macros Event Handling Summary\r
-\r
-For the full list of event classes, please see the\r
-@ref group_class_events "event classes group page".\r
-\r
-\r
-@todo for all controls state clearly when calling a member function results in an\r
- event being generated and when it doesn't (possibly updating also the\r
- 'Events generated by the user vs programmatically generated events' paragraph\r
- of the 'Event handling overview' with the list of the functions which break\r
- that rule).\r
-\r
-*/\r
-\r
+/////////////////////////////////////////////////////////////////////////////
+// Name: eventhandling.h
+// Purpose: topic overview
+// Author: wxWidgets team
+// RCS-ID: $Id$
+// Licence: wxWindows license
+/////////////////////////////////////////////////////////////////////////////
+
+/**
+
+@page overview_events Events and Event Handling
+
+Related classes: wxEvtHandler, wxWindow, wxEvent
+
+@li @ref overview_events_introduction
+@li @ref overview_events_eventhandling
+@li @ref overview_events_processing
+@li @ref overview_events_custom
+@li @ref overview_events_misc
+
+
+<hr>
+
+
+@section overview_events_introduction Introduction to Events
+
+Like with all the other GUI frameworks, the control of flow in wxWidgets
+applications is event-based: the program normally performs most of its actions
+in response to the events generated by the user. These events can be triggered
+by using the input devices (such as keyboard, mouse, joystick) directly or,
+more commonly, by a standard control which synthesizes such input events into
+higher level events: for example, a wxButton can generate a click event when
+the user presses the left mouse button on it and then releases it without
+pressing @c Esc in the meanwhile. There are also events which don't directly
+correspond to the user actions, such as wxTimerEvent or wxSocketEvent.
+
+But in all cases wxWidgets represents these events in a uniform way and allows
+you to handle them in the same way wherever they originate from. And while the
+events are normally generated by wxWidgets itself, you can also do this, which
+is especially useful when using custom events (see @ref overview_events_custom).
+
+To be more precise, each event is described by:
+ - <em>Event type</em>: this is simply a value of type wxEventType which
+ uniquely identifies the type of the event. For example, clicking on a button,
+ selecting an item from a list box and pressing a key on the keyboard all
+ generate events with different event types.
+ - <em>Event class</em> carried by the event: each event has some information
+ associated with it and this data is represented by an object of a class
+ derived from wxEvent. Events of different types can use the same event class,
+ for example both button click and listbox selection events use wxCommandEvent
+ class (as do all the other simple control events), but the key press event
+ uses wxKeyEvent as the information associated with it is different.
+ - <em>Event source</em>: wxEvent stores the object which generated the event
+ and, for windows, its identifier (see @ref overview_events_winid). As it is
+ common to have more than one object generating events of the same type (e.g. a
+ typical window contains several buttons, all generating the same button click
+ event), checking the event source object or its id allows to distinguish
+ between them.
+
+
+@section overview_events_eventhandling Event Handling
+
+There are two principal ways to handle events in wxWidgets. One of them uses
+<em>event table</em> macros and allows you to define the binding between events
+and their handlers only statically, i.e., during program compilation. The other
+one uses wxEvtHandler::Bind<>() call and can be used to bind and
+unbind, the handlers dynamically, i.e. during run-time depending on some
+conditions. It also allows the direct binding of events to:
+@li A handler method in another object.
+@li An ordinary function like a static method or a global function.
+@li An arbitrary functor like boost::function<>.
+
+The static event tables can only handle events in the object where they are
+defined so using Bind<>() is more flexible than using the event tables. On the
+other hand, event tables are more succinct and centralize all event handler
+bindings in one place. You can either choose a single approach that you find
+preferable or freely combine both methods in your program in different classes
+or even in one and the same class, although this is probably sufficiently
+confusing to be a bad idea.
+
+Also notice that most of the existing wxWidgets tutorials and discussions use
+the event tables because they historically preceded the apparition of dynamic
+event handling in wxWidgets. But this absolutely doesn't mean that using the
+event tables is the preferred way: handling events dynamically is better in
+several aspects and you should strongly consider doing it if you are just
+starting with wxWidgets. On the other hand, you still need to know about the
+event tables if only because you are going to see them in many samples and
+examples.
+
+So before you make the choice between static event tables and dynamically
+connecting the event handlers, let us discuss these two ways in more detail. In
+the next section we provide a short introduction to handling the events using
+the event tables. Please see @ref overview_events_bind for the discussion of
+Bind<>().
+
+@subsection overview_events_eventtables Event Handling with Event Tables
+
+To use an <em>event table</em> you must first decide in which class you wish to
+handle the events. The only requirement imposed by wxWidgets is that this class
+must derive from wxEvtHandler and so, considering that wxWindow derives from
+it, any classes representing windows can handle events. Simple events such as
+menu commands are usually processed at the level of a top-level window
+containing the menu, so let's suppose that you need to handle some events in @c
+MyFrame class deriving from wxFrame.
+
+First define one or more <em>event handlers</em>. They
+are just simple methods of the class that take as a parameter a
+reference to an object of a wxEvent-derived class and have no return value (any
+return information is passed via the argument, which is why it is non-const).
+You also need to insert a macro
+
+@code
+DECLARE_EVENT_TABLE()
+@endcode
+
+somewhere in the class declaration. It doesn't matter where it appears but
+it's customary to put it at the end because the macro changes the access
+type internally so it's safest if nothing follows it. The
+full class declaration might look like this:
+
+@code
+class MyFrame : public wxFrame
+{
+public:
+ MyFrame(...) : wxFrame(...) { }
+
+ ...
+
+protected:
+ int m_whatever;
+
+private:
+ // Notice that as the event handlers normally are not called from outside
+ // the class, they normally are private. In particular they don't need
+ // to be public.
+ void OnExit(wxCommandEvent& event);
+ void OnButton1(wxCommandEvent& event);
+ void OnSize(wxSizeEvent& event);
+
+ // it's common to call the event handlers OnSomething() but there is no
+ // obligation to do that; this one is an event handler too:
+ void DoTest(wxCommandEvent& event);
+
+ DECLARE_EVENT_TABLE()
+};
+@endcode
+
+Next the event table must be defined and, as with any definition, it must be
+placed in an implementation file. The event table tells wxWidgets how to map
+events to member functions and in our example it could look like this:
+
+@code
+BEGIN_EVENT_TABLE(MyFrame, wxFrame)
+ EVT_MENU(wxID_EXIT, MyFrame::OnExit)
+ EVT_MENU(DO_TEST, MyFrame::DoTest)
+ EVT_SIZE(MyFrame::OnSize)
+ EVT_BUTTON(BUTTON1, MyFrame::OnButton1)
+END_EVENT_TABLE()
+@endcode
+
+Notice that you must mention a method you want to use for the event handling in
+the event table definition; just defining it in MyFrame class is @e not enough.
+
+Let us now look at the details of this definition: the first line means that we
+are defining the event table for MyFrame class and that its base class is
+wxFrame, so events not processed by MyFrame will, by default, be handled by
+wxFrame. The next four lines define bindings of individual events to their
+handlers: the first two of them map menu commands from the items with the
+identifiers specified as the first macro parameter to two different member
+functions. In the next one, @c EVT_SIZE means that any changes in the size of
+the frame will result in calling OnSize() method. Note that this macro doesn't
+need a window identifier, since normally you are only interested in the current
+window's size events.
+
+The @c EVT_BUTTON macro demonstrates that the originating event does not have to
+come from the window class implementing the event table -- if the event source
+is a button within a panel within a frame, this will still work, because event
+tables are searched up through the hierarchy of windows for the command events.
+(But only command events, so you can't catch mouse move events in a child
+control in the parent window in the same way because wxMouseEvent doesn't
+derive from wxCommandEvent. See below for how you can do it.) In this case, the
+button's event table will be searched, then the parent panel's, then the
+frame's.
+
+Finally, you need to implement the event handlers. As mentioned before, all
+event handlers take a wxEvent-derived argument whose exact class differs
+according to the type of event and the class of the originating window. For
+size events, wxSizeEvent is used. For menu commands and most control commands
+(such as button presses), wxCommandEvent is used. When controls get more
+complicated, more specific wxCommandEvent-derived event classes providing
+additional control-specific information can be used, such as wxTreeEvent for
+events from wxTreeCtrl windows.
+
+In the simplest possible case an event handler may not use the @c event
+parameter at all. For example,
+
+@code
+void MyFrame::OnExit(wxCommandEvent& WXUNUSED(event))
+{
+ // when the user selects "Exit" from the menu we should close
+ Close(true);
+}
+@endcode
+
+In other cases you may need some information carried by the @c event argument,
+as in:
+
+@code
+void MyFrame::OnSize(wxSizeEvent& event)
+{
+ wxSize size = event.GetSize();
+
+ ... update the frame using the new size ...
+}
+@endcode
+
+You will find the details about the event table macros and the corresponding
+wxEvent-derived classes in the discussion of each control generating these
+events.
+
+
+@subsection overview_events_bind Dynamic Event Handling
+
+The possibilities of handling events in this way are rather different.
+Let us start by looking at the syntax: the first obvious difference is that you
+need not use DECLARE_EVENT_TABLE() nor BEGIN_EVENT_TABLE() and the
+associated macros. Instead, in any place in your code, but usually in
+the code of the class defining the handler itself (and definitely not in the
+global scope as with the event tables), call its Bind<>() method like this:
+
+@code
+MyFrame::MyFrame(...)
+{
+ Bind(wxEVT_COMMAND_MENU_SELECTED, &MyFrame::OnExit, this, wxID_EXIT);
+}
+@endcode
+
+Note that @c this pointer must be specified here.
+
+Now let us describe the semantic differences:
+<ul>
+ <li>
+ Event handlers can be bound at any moment. For example, it's possible
+ to do some initialization first and only bind the handlers if and when
+ it succeeds. This can avoid the need to test that the object was properly
+ initialized in the event handlers themselves. With Bind<>() they
+ simply won't be called if it wasn't correctly initialized.
+ </li>
+
+ <li>
+ As a slight extension of the above, the handlers can also be unbound at
+ any time with Unbind<>() (and maybe rebound later). Of course,
+ it's also possible to emulate this behaviour with the classic
+ static (i.e., bound via event tables) handlers by using an internal
+ flag indicating whether the handler is currently enabled and returning
+ from it if it isn't, but using dynamically bind handlers requires
+ less code and is also usually more clear.
+ </li>
+
+ <li>
+ Almost last but very, very far from least is the increased flexibility
+ which allows to bind an event to:
+ @li A method in another object.
+ @li An ordinary function like a static method or a global function.
+ @li An arbitrary functor like boost::function<>.
+
+ This is impossible to do with the event tables because it is not
+ possible to specify these handlers to dispatch the event to, so it
+ necessarily needs to be sent to the same object which generated the
+ event. Not so with Bind<>() which can be used to specify these handlers
+ which will handle the event. To give a quick example, a common question
+ is how to receive the mouse movement events happening when the mouse is
+ in one of the frame children in the frame itself. Doing it in a naive
+ way doesn't work:
+ <ul>
+ <li>
+ A @c EVT_LEAVE_WINDOW(MyFrame::OnMouseLeave) line in the frame
+ event table has no effect as mouse move (including entering and
+ leaving) events are not propagated up to the parent window
+ (at least not by default).
+ </li>
+
+ <li>
+ Putting the same line in a child event table will crash during
+ run-time because the MyFrame method will be called on a wrong
+ object -- it's easy to convince oneself that the only object
+ that can be used here is the pointer to the child, as
+ wxWidgets has nothing else. But calling a frame method with the
+ child window pointer instead of the pointer to the frame is, of
+ course, disastrous.
+ </li>
+ </ul>
+
+ However writing
+ @code
+ MyFrame::MyFrame(...)
+ {
+ m_child->Bind(wxEVT_LEAVE_WINDOW, &MyFrame::OnMouseLeave, this);
+ }
+ @endcode
+ will work exactly as expected. Note that you can get the object that
+ generated the event -- and that is not the same as the frame -- via
+ wxEvent::GetEventObject() method of @c event argument passed to the
+ event handler.
+ </li>
+
+ <li>
+ Really last point is the consequence of the previous one: because of
+ increased flexibility of Bind(), it is also safer as it is impossible
+ to accidentally use a method of another class. Instead of run-time
+ crashes you will get compilation errors in this case when using Bind().
+ </li>
+</ul>
+
+Let us now look at more examples of how to use different event handlers using
+the two overloads of Bind() function: first one for the object methods and the
+other one for arbitrary functors (callable objects, including simple functions):
+
+In addition to using a method of the object generating the event itself, you
+can use a method from a completely different object as an event handler:
+
+@code
+void MyFrameHandler::OnFrameExit( wxCommandEvent & )
+{
+ // Do something useful.
+}
+
+MyFrameHandler myFrameHandler;
+
+MyFrame::MyFrame()
+{
+ Bind( wxEVT_COMMAND_MENU_SELECTED, &MyFrameHandler::OnFrameExit,
+ &myFrameHandler, wxID_EXIT );
+}
+@endcode
+
+Note that @c MyFrameHandler doesn't need to derive from wxEvtHandler. But
+keep in mind that then the lifetime of @c myFrameHandler must be greater than
+that of @c MyFrame object -- or at least it needs to be unbound before being
+destroyed.
+
+
+To use an ordinary function or a static method as an event handler you would
+write something like this:
+
+@code
+void HandleExit( wxCommandEvent & )
+{
+ // Do something useful
+}
+
+MyFrame::MyFrame()
+{
+ Bind( wxEVT_COMMAND_MENU_SELECTED, &HandleExit, wxID_EXIT );
+}
+@endcode
+
+And finally you can bind to an arbitrary functor and use it as an event
+handler:
+
+@code
+
+struct MyFunctor
+{
+ void operator()( wxCommandEvent & )
+ {
+ // Do something useful
+ }
+};
+
+MyFunctor myFunctor;
+
+MyFrame::MyFrame()
+{
+ Bind( wxEVT_COMMAND_MENU_SELECTED, &myFunctor, wxID_EXIT );
+}
+@endcode
+
+A common example of a functor is boost::function<>:
+
+@code
+using namespace boost;
+
+void MyHandler::OnExit( wxCommandEvent & )
+{
+ // Do something useful
+}
+
+MyHandler myHandler;
+
+MyFrame::MyFrame()
+{
+ function< void ( wxCommandEvent & ) > exitHandler( bind( &MyHandler::OnExit, &myHandler, _1 ));
+
+ Bind( wxEVT_COMMAND_MENU_SELECTED, exitHandler, wxID_EXIT );
+}
+@endcode
+
+
+With the aid of boost::bind<>() you can even use methods or functions which
+don't quite have the correct signature:
+
+@code
+void MyHandler::OnExit( int exitCode, wxCommandEvent &, wxString goodByeMessage )
+{
+ // Do something useful
+}
+
+MyHandler myHandler;
+
+MyFrame::MyFrame()
+{
+ function< void ( wxCommandEvent & ) > exitHandler(
+ bind( &MyHandler::OnExit, &myHandler, EXIT_FAILURE, _1, "Bye" ));
+
+ Bind( wxEVT_COMMAND_MENU_SELECTED, exitHandler, wxID_EXIT );
+}
+@endcode
+
+
+To summarize, using Bind<>() requires slightly more typing but is much more
+flexible than using static event tables so don't hesitate to use it when you
+need this extra power. On the other hand, event tables are still perfectly fine
+in simple situations where this extra flexibility is not needed.
+
+
+@section overview_events_processing How Events are Processed
+
+The previous sections explain how to define event handlers but don't address
+the question of how exactly wxWidgets finds the handler to call for the
+given event. This section describes the algorithm used in detail.
+
+When an event is received from the windowing system, wxWidgets calls
+wxEvtHandler::ProcessEvent() on the first event handler object belonging to the
+window generating the event. The normal order of event table searching by
+ProcessEvent() is as follows, with the event processing stopping as soon as a
+handler is found (unless the handler calls wxEvent::Skip() in which case it
+doesn't count as having handled the event and the search continues):
+<ol>
+ <li value="0">
+ Before anything else happens, wxApp::FilterEvent() is called. If it returns
+ anything but -1 (default), the event handling stops immediately.
+ </li>
+
+ <li value="1">
+ If this event handler is disabled via a call to
+ wxEvtHandler::SetEvtHandlerEnabled() the next three steps are skipped and
+ the event handler resumes at step (5).
+ </li>
+
+ <li value="2">
+ If the object is a wxWindow and has an associated validator, wxValidator
+ gets a chance to process the event.
+ </li>
+
+ <li value="3">
+ The list of dynamically bind event handlers, i.e., those for which
+ Bind<>() was called, is consulted. Notice that this is done before
+ checking the static event table entries, so if both a dynamic and a static
+ event handler match the same event, the static one is never going to be
+ used.
+ </li>
+
+ <li value="4">
+ The event table containing all the handlers defined using the event table
+ macros in this class and its base classes is examined. Notice that this
+ means that any event handler defined in a base class will be executed at
+ this step.
+ </li>
+
+ <li value="5">
+ The event is passed to the next event handler, if any, in the event handler
+ chain, i.e., the steps (1) to (4) are done for it. This chain can be formed
+ using wxEvtHandler::SetNextHandler():
+ @image html overview_events_chain.png
+ (referring to the image, if @c A->ProcessEvent is called and it doesn't handle
+ the event, @c B->ProcessEvent will be called and so on...).
+ In the case of wxWindow you can build a stack (implemented using wxEvtHandler
+ double-linked list) using wxWindow::PushEventHandler():
+ @image html overview_events_winstack.png
+ (referring to the image, if @c W->ProcessEvent is called, it immediately calls
+ @c A->ProcessEvent; if nor @c A nor @c B handle the event, then the wxWindow
+ itself is used - i.e. the dynamically bind event handlers and static
+ event table entries of wxWindow are looked as the last possibility, after
+ all pushed event handlers were tested).
+ Note however that usually there are no wxEvtHandler chains nor wxWindows stacks
+ so this step will usually do anything.
+ </li>
+
+ <li value="6">
+ If the object is a wxWindow and the event is set to propagate (by default
+ only wxCommandEvent-derived events are set to propagate), then the
+ processing restarts from the step (1) (and excluding the step (7)) for the
+ parent window. If this object is not a window but the next handler exists,
+ the event is passed to its parent if it is a window. This ensures that in a
+ common case of (possibly several) non-window event handlers pushed on top
+ of a window, the event eventually reaches the window parent.
+ </li>
+
+ <li value="7">
+ Finally, i.e., if the event is still not processed, the wxApp object itself
+ (which derives from wxEvtHandler) gets a last chance to process it.
+ </li>
+</ol>
+
+<em>Please pay close attention to step 6!</em> People often overlook or get
+confused by this powerful feature of the wxWidgets event processing system. The
+details of event propagation up the window hierarchy are described in the
+next section.
+
+Also please notice that there are additional steps in the event handling for
+the windows-making part of wxWidgets document-view framework, i.e.,
+wxDocParentFrame, wxDocChildFrame and their MDI equivalents wxDocMDIParentFrame
+and wxDocMDIChildFrame. The parent frame classes modify step (2) above to
+send the events received by them to wxDocManager object first. This object, in
+turn, sends the event to the current view and the view itself lets its
+associated document process the event first. The child frame classes send
+the event directly to the associated view which still forwards it to its
+document object. Notice that to avoid remembering the exact order in which the
+events are processed in the document-view frame, the simplest, and recommended,
+solution is to only handle the events at the view classes level, and not in the
+document or document manager classes
+
+
+@subsection overview_events_propagation How Events Propagate Upwards
+
+As mentioned above, the events of the classes deriving from wxCommandEvent are
+propagated by default to the parent window if they are not processed in this
+window itself. But although by default only the command events are propagated
+like this, other events can be propagated as well because the event handling
+code uses wxEvent::ShouldPropagate() to check whether an event should be
+propagated. It is also possible to propagate the event only a limited number of
+times and not until it is processed (or a top level parent window is reached).
+
+Finally, there is another additional complication (which, in fact, simplifies
+life of wxWidgets programmers significantly): when propagating the command
+events up to the parent window, the event propagation stops when it
+reaches the parent dialog, if any. This means that you don't risk getting
+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 difficult, if not impossible, to track down all the dialogs that
+may be popped up in a complex program (remember that some are created
+automatically by wxWidgets). If you need to specify a different behaviour for
+some reason, you can use wxWindow::SetExtraStyle(wxWS_EX_BLOCK_EVENTS)
+explicitly to prevent the events from being propagated beyond the given window
+or unset this flag for the dialogs that 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 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.
+More precisely, as said above, all event classes @b not deriving from wxCommandEvent
+(see the wxEvent inheritance map) do @b not propagate upward.
+
+In some cases, it might be desired by the programmer to get a certain number
+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.
+
+
+@section overview_events_custom Custom Event Summary
+
+@subsection overview_events_custom_general General approach
+
+As each event is uniquely defined by its event type, defining a custom event
+starts with defining a new event type for it. This is done using
+wxDEFINE_EVENT() macro. As an event type is a variable, it can also be
+declared using wxDECLARE_EVENT() if necessary.
+
+The next thing to do is to decide whether you need to define a custom event
+class for events of this type or if you can reuse an existing class, typically
+either wxEvent (which doesn't provide any extra information) or wxCommandEvent
+(which contains several extra fields and also propagates upwards by default).
+Both strategies are described in details below. See also the @ref
+page_samples_event for a complete example of code defining and working with the
+custom event types.
+
+
+@subsection overview_events_custom_existing Using Existing Event Classes
+
+If you just want to use a wxCommandEvent with a new event type, use one of the
+generic event table macros listed below, without having to define a new event
+class yourself.
+
+Example:
+
+@code
+// this is typically in a header: it just declares MY_EVENT event type
+wxDECLARE_EVENT(MY_EVENT, wxCommandEvent);
+
+// this is a definition so can't be in a header
+wxDEFINE_EVENT(MY_EVENT, wxCommandEvent);
+
+// example of code handling the event with event tables
+BEGIN_EVENT_TABLE(MyFrame, wxFrame)
+ EVT_MENU (wxID_EXIT, MyFrame::OnExit)
+ ...
+ EVT_COMMAND (ID_MY_WINDOW, MY_EVENT, MyFrame::OnMyEvent)
+END_EVENT_TABLE()
+
+void MyFrame::OnMyEvent(wxCommandEvent& event)
+{
+ // do something
+ wxString text = event.GetText();
+}
+
+// example of code handling the event with Bind<>():
+MyFrame::MyFrame()
+{
+ Bind(MY_EVENT, &MyFrame::OnMyEvent, this, ID_MY_WINDOW);
+}
+
+// example of code generating the event
+void MyWindow::SendEvent()
+{
+ wxCommandEvent event(MY_EVENT, GetId());
+ event.SetEventObject(this);
+
+ // Give it some contents
+ event.SetText("Hello");
+
+ // Do send it
+ ProcessWindowEvent(event);
+}
+@endcode
+
+
+@subsection overview_events_custom_ownclass Defining Your Own Event Class
+
+Under certain circumstances, you must define your own event class e.g., for
+sending more complex data from one place to another. Apart from defining your
+event class, you also need to define your own event table macro if you want to
+use event tables for handling events of this type.
+
+Here is an example:
+
+@code
+// define a new event class
+class MyPlotEvent: public wxEvent
+{
+public:
+ MyPlotEvent(wxEventType eventType, int winid, const wxPoint& pos)
+ : wxEvent(winid, eventType),
+ m_pos(pos)
+ {
+ }
+
+ // accessors
+ wxPoint GetPoint() const { return m_pos; }
+
+ // implement the base class pure virtual
+ virtual wxEvent *Clone() const { return new MyPlotEvent(*this); }
+
+private:
+ const wxPoint m_pos;
+};
+
+// we define a single MY_PLOT_CLICKED event type associated with the class
+// above but typically you are going to have more than one event type, e.g. you
+// could also have MY_PLOT_ZOOMED or MY_PLOT_PANNED &c -- in which case you
+// would just add more similar lines here
+wxDEFINE_EVENT(MY_PLOT_CLICKED, MyPlotEvent);
+
+
+// if you want to support old compilers you need to use some ugly macros:
+typedef void (wxEvtHandler::*MyPlotEventFunction)(MyPlotEvent&);
+#define MyPlotEventHandler(func) wxEVENT_HANDLER_CAST(MyPlotEventFunction, func)
+
+// if your code is only built using reasonably modern compilers, you could just
+// do this instead:
+#define MyPlotEventHandler(func) (&func)
+
+// finally define a macro for creating the event table entries for the new
+// event type
+//
+// remember that you don't need this at all if you only use Bind<>() and that
+// you can replace MyPlotEventHandler(func) with just &func unless you use a
+// really old compiler
+#define MY_EVT_PLOT_CLICK(id, func) \
+ wx__DECLARE_EVT1(MY_PLOT_CLICKED, id, MyPlotEventHandler(func))
+
+
+// example of code handling the event (you will use one of these methods, not
+// both, of course):
+BEGIN_EVENT_TABLE(MyFrame, wxFrame)
+ EVT_PLOT(ID_MY_WINDOW, MyFrame::OnPlot)
+END_EVENT_TABLE()
+
+MyFrame::MyFrame()
+{
+ Bind(MY_PLOT_CLICKED, &MyFrame::OnPlot, this, ID_MY_WINDOW);
+}
+
+void MyFrame::OnPlot(MyPlotEvent& event)
+{
+ ... do something with event.GetPoint() ...
+}
+
+
+// example of code generating the event:
+void MyWindow::SendEvent()
+{
+ MyPlotEvent event(MY_PLOT_CLICKED, GetId(), wxPoint(...));
+ event.SetEventObject(this);
+ ProcessWindowEvent(event);
+}
+@endcode
+
+
+
+@section overview_events_misc Miscellaneous Notes
+
+@subsection overview_events_virtual Event Handlers vs Virtual Methods
+
+It may be noted that wxWidgets' event processing system implements something
+close to virtual methods in normal C++ in spirit: both of these mechanisms
+allow you to alter the behaviour of the base class by defining the event handling
+functions in the derived classes.
+
+There is however an important difference between the two mechanisms when you
+want to invoke the default behaviour, as implemented by the base class, from a
+derived class handler. With the virtual functions, you need to call the base
+class function directly and you can do it either in the beginning of the
+derived class handler function (to post-process the event) or at its end (to
+pre-process the event). With the event handlers, you only have the option of
+pre-processing the events and in order to still let the default behaviour
+happen you must call wxEvent::Skip() and @em not call the base class event
+handler directly. In fact, the event handler probably doesn't even exist in the
+base class as the default behaviour is often implemented in platform-specific
+code by the underlying toolkit or OS itself. But even if it does exist at
+wxWidgets level, it should never be called directly as the event handlers are
+not part of wxWidgets API and should never be called directly.
+
+
+
+@subsection overview_events_prog User Generated Events vs Programmatically Generated Events
+
+While generically wxEvents can be generated both by user
+actions (e.g., resize of a wxWindow) and by calls to functions
+(e.g., wxWindow::SetSize), wxWidgets controls normally send wxCommandEvent-derived
+events only for the user-generated events. The only @b exceptions to this rule are:
+
+@li wxNotebook::AddPage: No event-free alternatives
+@li wxNotebook::AdvanceSelection: No event-free alternatives
+@li wxNotebook::DeletePage: No event-free alternatives
+@li wxNotebook::SetSelection: Use wxNotebook::ChangeSelection instead, as
+ wxNotebook::SetSelection is deprecated
+@li wxTreeCtrl::Delete: No event-free alternatives
+@li wxTreeCtrl::DeleteAllItems: No event-free alternatives
+@li wxTreeCtrl::EditLabel: No event-free alternatives
+@li All wxTextCtrl methods
+
+wxTextCtrl::ChangeValue can be used instead of wxTextCtrl::SetValue but the other
+functions, such as wxTextCtrl::Replace or wxTextCtrl::WriteText don't have event-free
+equivalents.
+
+
+
+@subsection overview_events_pluggable Pluggable Event Handlers
+
+<em>TODO: Probably deprecated, Bind() provides a better way to do this</em>
+
+In fact, you don't have to derive a new class from a window class
+if you don't want to. You can derive a new class from wxEvtHandler instead,
+defining the appropriate event table, and then call wxWindow::SetEventHandler
+(or, preferably, wxWindow::PushEventHandler) to make this
+event handler the object that responds to events. This way, you can avoid
+a lot of class derivation, and use instances of the same event handler class (but different
+objects as the same event handler object shouldn't be used more than once) to
+handle events from instances of different widget classes.
+
+If you ever have to call a window's event handler
+manually, use the GetEventHandler function to retrieve the window's event handler and use that
+to call the member function. By default, GetEventHandler returns a pointer to the window itself
+unless an application has redirected event handling using SetEventHandler or PushEventHandler.
+
+One use of PushEventHandler is to temporarily or permanently change the
+behaviour of the GUI. For example, you might want to invoke a dialog editor
+in your application that changes aspects of dialog boxes. You can
+grab all the input for an existing dialog box, and edit it 'in situ',
+before restoring its behaviour to normal. So even if the application
+has derived new classes to customize behaviour, your utility can indulge
+in a spot of body-snatching. It could be a useful technique for on-line
+tutorials, too, where you take a user through a serious of steps and
+don't want them to diverge from the lesson. Here, you can examine the events
+coming from buttons and windows, and if acceptable, pass them through to
+the original event handler. Use PushEventHandler/PopEventHandler
+to form a chain of event handlers, where each handler processes a different
+range of events independently from the other handlers.
+
+
+
+@subsection overview_events_winid Window Identifiers
+
+Window identifiers are integers, and are used to
+uniquely determine window identity in the event system (though you can use it
+for other purposes). In fact, identifiers do not need to be unique
+across your entire application as long they are unique within the
+particular context you're interested in, such as a frame and its children. You
+may use the @c wxID_OK identifier, for example, on any number of dialogs
+as long as you don't have several within the same dialog.
+
+If you pass @c wxID_ANY to a window constructor, an identifier will be
+generated for you automatically by wxWidgets. This is useful when you don't
+care about the exact identifier either because you're not going to process the
+events from the control being created or because you process the events
+from all controls in one place (in which case you should specify @c wxID_ANY
+in the event table or wxEvtHandler::Bind call
+as well). The automatically generated identifiers are always negative and so
+will never conflict with the user-specified identifiers which must be always
+positive.
+
+See @ref page_stdevtid for the list of standard identifiers available.
+You can use wxID_HIGHEST to determine the number above which it is safe to
+define your own identifiers. Or, you can use identifiers below wxID_LOWEST.
+Finally, you can allocate identifiers dynamically using wxNewId() function too.
+If you use wxNewId() consistently in your application, you can be sure that
+your identifiers don't conflict accidentally.
+
+
+@subsection overview_events_custom_generic Generic Event Table Macros
+
+@beginTable
+@row2col{EVT_CUSTOM(event\, id\, func),
+ Allows you to add a custom event table
+ entry by specifying the event identifier (such as wxEVT_SIZE),
+ the window identifier, and a member function to call.}
+@row2col{EVT_CUSTOM_RANGE(event\, id1\, id2\, func),
+ The same as EVT_CUSTOM, but responds to a range of window identifiers.}
+@row2col{EVT_COMMAND(id\, event\, func),
+ The same as EVT_CUSTOM, but expects a member function with a
+ wxCommandEvent argument.}
+@row2col{EVT_COMMAND_RANGE(id1\, id2\, event\, func),
+ The same as EVT_CUSTOM_RANGE, but
+ expects a member function with a wxCommandEvent argument.}
+@row2col{EVT_NOTIFY(event\, id\, func),
+ The same as EVT_CUSTOM, but
+ expects a member function with a wxNotifyEvent argument.}
+@row2col{EVT_NOTIFY_RANGE(event\, id1\, id2\, func),
+ The same as EVT_CUSTOM_RANGE, but
+ expects a member function with a wxNotifyEvent argument.}
+@endTable
+
+
+
+@subsection overview_events_list List of wxWidgets events
+
+For the full list of event classes, please see the
+@ref group_class_events "event classes group page".
+
+
+*/
+
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