36c9828f70
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@51911 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
126 lines
4.2 KiB
C++
126 lines
4.2 KiB
C++
/////////////////////////////////////////////////////////////////////////////
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// Name: app
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// Purpose: topic overview
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// Author: wxWidgets team
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// RCS-ID: $Id$
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// Licence: wxWindows license
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/////////////////////////////////////////////////////////////////////////////
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/*!
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@page app_overview wxApp overview
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Classes: #wxApp
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A wxWidgets application does not have a @e main procedure; the equivalent is the
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#OnInit member defined for a class derived from wxApp.
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@e OnInit will usually create a top window as a bare minimum.
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Unlike in earlier versions of wxWidgets, OnInit does not return a frame. Instead it
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returns a boolean value which indicates whether processing should continue (@true) or not (@false).
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You call wxApp::SetTopWindow to let wxWidgets know
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about the top window.
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Note that the program's command line arguments, represented by @e argc
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and @e argv, are available from within wxApp member functions.
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An application closes by destroying all windows. Because all frames must
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be destroyed for the application to exit, it is advisable to use parent
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frames wherever possible when creating new frames, so that deleting the
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top level frame will automatically delete child frames. The alternative
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is to explicitly delete child frames in the top-level frame's #wxCloseEvent
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handler.
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In emergencies the #wxExit function can be called to kill the
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application however normally the application shuts down automatically,
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@ref appshutdown_overview.
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An example of defining an application follows:
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@code
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class DerivedApp : public wxApp
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{
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public:
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virtual bool OnInit();
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};
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IMPLEMENT_APP(DerivedApp)
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bool DerivedApp::OnInit()
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{
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wxFrame *the_frame = new wxFrame(@NULL, ID_MYFRAME, argv[0]);
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...
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the_frame-Show(@true);
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SetTopWindow(the_frame);
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return @true;
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}
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@endcode
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Note the use of IMPLEMENT_APP(appClass), which allows wxWidgets to dynamically create an instance of the application object
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at the appropriate point in wxWidgets initialization. Previous versions of wxWidgets used
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to rely on the creation of a global application object, but this is no longer recommended,
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because required global initialization may not have been performed at application object
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construction time.
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You can also use DECLARE_APP(appClass) in a header file to declare the wxGetApp function which returns
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a reference to the application object. Otherwise you can only use the global
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@c wxTheApp pointer which is of type @c wxApp *.
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@ref appshutdown_overview
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@section wxappshutdownoverview Application shutdown
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The application normally shuts down when the last of its top level windows is
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closed. This is normally the expected behaviour and means that it is enough to
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call #Close() in response to the @c "Exit" menu
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command if your program has a single top level window. If this behaviour is not
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desirable wxApp::SetExitOnFrameDelete can
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be called to change it. Note that starting from wxWidgets 2.3.3 such logic
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doesn't apply for the windows shown before the program enters the main loop: in
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other words, you can safely show a dialog from
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wxApp::OnInit and not be afraid that your application
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terminates when this dialog -- which is the last top level window for the
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moment -- is closed.
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Another aspect of the application shutdown is #OnExit
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which is called when the application exits but @e before wxWidgets cleans up
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its internal structures. You should delete all wxWidgets object that you
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created by the time OnExit finishes. In particular, do @b not destroy them
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from application class' destructor!
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For example, this code may crash:
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@code
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class MyApp : public wxApp
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{
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public:
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wxCHMHelpController m_helpCtrl;
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...
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};
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@endcode
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The reason for that is that @c m_helpCtrl is a member object and is
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thus destroyed from MyApp destructor. But MyApp object is deleted after
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wxWidgets structures that wxCHMHelpController depends on were
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uninitialized! The solution is to destroy HelpCtrl in @e OnExit:
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@code
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class MyApp : public wxApp
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{
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public:
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wxCHMHelpController *m_helpCtrl;
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...
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};
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bool MyApp::OnInit()
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{
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...
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m_helpCtrl = new wxCHMHelpController;
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...
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}
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int MyApp::OnExit()
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{
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delete m_helpCtrl;
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return 0;
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}
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@endcode
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*/
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