Amebis/wxWidgets
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

many document corrections by charles; partial commit of patch #10087

Browse Source 
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@56945 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
This commit is contained in:
Francesco Montorsi
2008-11-23 19:46:43 +00:00
parent 6d62b2e2b1
commit d76259e2fb
1 changed files with 80 additions and 82 deletions
Download Patch File Download Diff File Expand all files Collapse all files

162
docs/doxygen/overviews/eventhandling.h
View File

@@ -32,21 +32,21 @@ Classes: wxEvtHandler, wxWindow, wxEvent
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 connection between events
and their handlers only statically, i.e. during program compilation. The other
and their handlers only statically, i.e., during program compilation. The other
one uses wxEvtHandler::Connect() call and can be used to connect, and
disconnect, the handlers dynamically, i.e. during run-time depending on some
conditions. It also allows directly connecting the events of one object to a
handler method in another object while the static event tables can only handle
disconnect, the handlers dynamically, i.e., during run-time depending on some
conditions. It also allows the direct connection of the events of one object to a
handler method in another object. The static event tables can only handle
events in the object where they are defined so using Connect() is more flexible
than using the event tables. On the other hand, event tables are more succinct
and centralize all event handlers connection in one place. You can either
choose a single approach which you find preferable or freely combine both
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.
But before you make this choice, let us discuss these two ways in some more
details: in the next section we provide a short introduction to handling the
events using the event tables, please see @ref overview_eventhandling_connect
But before you make this choice, 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_eventhandling_connect
for the discussion of Connect().
@section overview_eventhandling_eventtables Event Handling with Event Tables
@@ -59,9 +59,9 @@ 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 thing to do is to define one or more <em>event handlers</em>. They
are just simple (non-virtual) methods of the class which take as a parameter a
reference to an object of wxEvent-derived class and have no return value (any
First define one or more <em>event handlers</em>. They
are just simple (non-virtual) 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
@@ -69,9 +69,9 @@ You also need to insert a macro
DECLARE_EVENT_TABLE()
@endcode
somewhere in the class declaration. It doesn't matter where does it occur but
it's customary to put it at the end of it because the macro changes the access
type internally and so it's safest if there is nothing that follows it. So the
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
@@ -86,23 +86,23 @@ protected:
int m_whatever;
private:
// notice that as the event handlers normally are not called from outside
// the class, they normally be private, in particular they don't need at
// all to be public
// 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 it, this one is an event handler too:
// 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 any definition, it must be placed
in an implementation file to tell. The event table tells wxWidgets how to map
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
@@ -115,11 +115,11 @@ 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.
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 to
wxFrame, so events not processed by MyFrame will, by default, be handled by
wxFrame. The next four lines define connections 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
@@ -131,10 +131,10 @@ window's size events.
The 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
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
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.
@@ -142,16 +142,16 @@ 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. And when controls get more
(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, e.g.
parameter at all. For example,
@code
void MyFrame::OnExit(wxCommandEvent&)
void MyFrame::OnExit(wxCommandEvent& WXUNUSED(event))
{
// when the user selects "Exit" from the menu we should close
Close(true);
@@ -177,19 +177,17 @@ events.
@section overview_eventhandling_connect Dynamic Event Handling
As with the event tables, you need to decide in which class do you intend to
handle the events first and, also as before, this class must still derive from
wxEvtHandler (usually indirectly via wxWindow), see the declaration of MyFrame
As with the event tables, decide in which class you intend to
handle the events first and, as before, this class must derive from
wxEvtHandler (usually indirectly via wxWindow). See the declaration of MyFrame
in the previous section. However the similarities end here and both the syntax
and the possibilities of this way of handling events in this way are rather
different.
and 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
don't need to use neither @c DECLARE_EVENT_TABLE() nor @c BEGIN_EVENT_TABLE and
associated macros any more. Instead, in any place in your code, but usually in
the code of the class defining the handlers itself (and definitely not in the
global scope as with the event tables), you should call its Connect() method
like this:
need not use @c DECLARE_EVENT_TABLE() nor @c 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 Connect() method like this:
@code
MyFrame::MyFrame(...)
@@ -200,24 +198,24 @@ MyFrame::MyFrame(...)
@endcode
This class should be self-explanatory except for wxCommandEventHandler part:
this is a macro which ensures that the method is of correct type by using
static_cast in the same way as event table macros do it inside them.
this is a macro that ensures that the method is of the correct type by using
static_cast in the same way as the event table macros.
Now let us describe the semantic differences:
<ul>
<li>
Event handlers can be connected at any moment, e.g. it's possible to do
some initialization first and only connect 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 Connect() they
simply won't be called at all if it wasn't.
Event handlers can be connected at any moment. For example, it's possible
to do some initialization first and only connect 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 Connect() 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
Disconnect()-ed at any time. And maybe later reconnected again. Of
course, it's also possible to emulate this behaviour with the classic
static (i.e. connected via event tables) handlers by using an internal
Disconnect()-ed at any time and maybe later reconnected. Of course,
it's also possible to emulate this behaviour with the classic
static (i.e., connected 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 connected handlers requires
less code and is also usually more clear.
@@ -235,12 +233,12 @@ Now let us describe the semantic differences:
<li>
Last but very, very far from least is the possibility to connect an
event of some object to a method of another object. This is impossible
to do with event tables because there is no possibility to specify the
to do with event tables because it is not possible to specify the
object to dispatch the event to so it necessarily needs to be sent to
the same object which generated the event. Not so with Connect() which
has an optional @c eventSink parameter which can be used to specify the
has an optional @c eventSink parameter that can be used to specify the
object which will handle the event. Of course, in this case the method
being connected must belong to the class which is the type of the
being connected must belong to the class that is the type of the
@c eventSink object! To give a quick example, people often want to catch
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:
@@ -248,7 +246,7 @@ Now let us describe the semantic differences:
<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 upwards to the parent window
leaving) events are not propagated up to the parent window
(at least not by default).
</li>
@@ -256,7 +254,7 @@ Now let us describe the semantic differences:
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
which can be used here is the pointer to the child, as
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.
@@ -273,8 +271,8 @@ Now let us describe the semantic differences:
this); // this indicates the object to connect to
}
@endcode
will work exactly as expected. Note that you can get the object which
generated the event -- and which is not the same as the frame -- via
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>
@@ -289,8 +287,8 @@ in simple situations where this extra flexibility is not needed.
@section overview_eventhandling_processing How Events are Processed
The previous sections explain how to define event handlers but don't address
the question of how exactly does wxWidgets find the handler to call for the
given event. This section describes the algorithm used to do it in details.
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
@@ -308,7 +306,7 @@ doesn't count as having handled the event and the search continues):
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>
<li value="2">
If the object is a wxWindow and has an associated validator, wxValidator
@@ -316,7 +314,7 @@ doesn't count as having handled the event and the search continues):
</li>
<li value="3">
The list of dynamically connected event handlers, i.e. those for which
The list of dynamically connected event handlers, i.e., those for which
Connect() 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
@@ -332,7 +330,7 @@ doesn't count as having handled the event and the search continues):
<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
chain, i.e., the steps (1) to (4) are done for it. This chain can be formed
using wxEvtHandler::SetNextHandler() or wxWindow::PushEventHandler() but
usually there is no next event handler and chaining event handlers using
these functions is much less useful now that Connect() exists so this step
@@ -350,27 +348,27 @@ doesn't count as having handled the event and the search continues):
</li>
<li value="7">
Finally, i.e. if the event is still not processed, the wxApp object itself
Finally, i.e., if the event is still not processed, the wxApp object itself
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 upwards the window hierarchy are described in 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.
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 the step (2) above to
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 to process the event first. The child frame classes send
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, but not in the
solution is to only handle the events at the view classes level, and not in the
document or document manager classes
@@ -380,36 +378,36 @@ As mentioned in the previous section, 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 for whether an
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 upwards to the parent window, the event propagation stops when it
reaches the parent dialog, if any. This means that you don't risk to get
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 very difficult, if not impossible, to track down all the dialogs which
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 which have it on by default.
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 and/or are generated by the window
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.
As mentioned above, only command events are recursively applied to the parents
event handler in the library itself. As this quite often causes confusion for
users, here is a list of system events which will @em not get sent to the
users, here is a list of system events that will @em not get sent to the
parent's event handler:
@li wxEvent: The event base class
@@ -442,7 +440,7 @@ all events (or any selection of them) to the parent window.
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 to alter the behaviour of the base class by defining the event handling
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
@@ -451,12 +449,12 @@ 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 to
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 handler are
wxWidgets level, it should never be called directly as the event handlers are
not part of wxWidgets API and should never be called directly.
Finally, please notice that the event handlers themselves shouldn't be virtual.
@@ -467,8 +465,8 @@ make them public) methods of a wxEvtHandler-derived class.
@section overview_eventhandling_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
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
@@ -524,7 +522,7 @@ range of events independently from the other handlers.
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 just so long as they are unique within a
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 so
long as you don't have several within the same dialog.
@@ -647,8 +645,8 @@ void MyWindow::SendEvent()
@subsection overview_eventhandling_custom_ownclass Defining Your Own Event Class
Under certain circumstances, it will be required to define your own event
class e.g. for sending more complex data from one place to another. Apart
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 will also need to define your own
event table macro (which is quite long). Watch out to put in enough
casts to the inherited event function. Here is an example: