-/*!
-
- @page overview_app wxApp overview
-
- Classes: #wxApp
- A wxWidgets application does not have a @e main procedure; the equivalent is the
- #OnInit member defined for a class derived from wxApp.
-
- @e OnInit will usually create a top window as a bare minimum.
- Unlike in earlier versions of wxWidgets, OnInit does not return a frame. Instead it
- returns a boolean value which indicates whether processing should continue (@true)
- or not (@false). You call wxApp::SetTopWindow to let wxWidgets know about the top window.
-
- Note that the program's command line arguments, represented by @e argc
- and @e argv, are available from within wxApp member functions.
-
- An application closes by destroying all windows. Because all frames must
- be destroyed for the application to exit, it is advisable to use parent
- frames wherever possible when creating new frames, so that deleting the
- top level frame will automatically delete child frames. The alternative
- is to explicitly delete child frames in the top-level frame's #wxCloseEvent
- handler.
-
- In emergencies the #wxExit function can be called to kill the
- application however normally the application shuts down automatically,
- see @ref overview_app_shutdown.
-
- An example of defining an application follows:
-
- @code
- class DerivedApp : public wxApp
- {
- public:
- virtual bool OnInit();
- };
-
- IMPLEMENT_APP(DerivedApp)
-
- bool DerivedApp::OnInit()
- {
- wxFrame *the_frame = new wxFrame(@NULL, ID_MYFRAME, argv[0]);
- ...
- the_frame-Show(@true);
- SetTopWindow(the_frame);
-
- return @true;
- }
- @endcode
-
- Note the use of IMPLEMENT_APP(appClass), which allows wxWidgets to dynamically create
- an instance of the application object at the appropriate point in wxWidgets initialization.
- Previous versions of wxWidgets used to rely on the creation of a global application object,
- but this is no longer recommended, because required global initialization may not have
- been performed at application object construction time.
-
- You can also use DECLARE_APP(appClass) in a header file to declare the wxGetApp function
- which returns a reference to the application object. Otherwise you can only use the global
- @c wxTheApp pointer which is of type @c wxApp *.
-
-
-
- @section overview_app_shutdown Application shutdown
-
- The application normally shuts down when the last of its top level windows is
- closed. This is normally the expected behaviour and means that it is enough to
- call #Close() in response to the @c "Exit" menu command if your program has a single
- top level window. If this behaviour is not desirable wxApp::SetExitOnFrameDelete can
- be called to change it.
-
- Note that starting from wxWidgets 2.3.3 such logic doesn't apply for the windows shown
- before the program enters the main loop: in other words, you can safely show a dialog from
- wxApp::OnInit and not be afraid that your application terminates when this dialog --
- which is the last top level window for the moment -- is closed.
-
- Another aspect of the application shutdown is #OnExit
- which is called when the application exits but @e before wxWidgets cleans up
- its internal structures. You should delete all wxWidgets object that you
- created by the time OnExit finishes.
-
- In particular, do @b not destroy them from application class' destructor!
- For example, this code may crash:
-
- @code
- class MyApp : public wxApp
- {
- public:
- wxCHMHelpController m_helpCtrl;
- ...
- };
- @endcode
-
- The reason for that is that @c m_helpCtrl is a member object and is
- thus destroyed from MyApp destructor. But MyApp object is deleted after
- wxWidgets structures that wxCHMHelpController depends on were
- uninitialized! The solution is to destroy HelpCtrl in @e OnExit:
-
- @code
- class MyApp : public wxApp
- {
- public:
- wxCHMHelpController *m_helpCtrl;
- ...
- };
-
- bool MyApp::OnInit()
- {
- ...
- m_helpCtrl = new wxCHMHelpController;
- ...
- }
-
- int MyApp::OnExit()
- {
- delete m_helpCtrl;
- return 0;
- }
- @endcode
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