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[wxWidgets.git] / docs / doxygen / overviews / helloworld.h

/////////////////////////////////////////////////////////////////////////////
// Name:        helloworld.h
// Purpose:     topic overview
// Author:      wxWidgets team
// RCS-ID:      $Id$
// Licence:     wxWindows license
/////////////////////////////////////////////////////////////////////////////

/*!

 @page overview_helloworld wxWidgets Hello World sample

 Many people have requested a mini-sample to be published here
 so that some quick judgment concerning syntax
 and basic principles can be made, so here we go.

 First, you have to include wxWidgets' header files, of course. This can
 be done on a file by file basis (such as <tt>@#include "wx/window.h"</tt>)
 or using one global include (<tt>@#include "wx/wx.h"</tt>). This is
 also useful on platforms which support precompiled headers such
 as all major compilers on the Windows platform and GCC on Unix platforms.

 @code
 //
 // file name: hworld.cpp
 //
 //   purpose: wxWidgets "Hello world"
 //

 // For compilers that support precompilation, includes "wx/wx.h".
 #include "wx/wxprec.h"

 #ifdef __BORLANDC__
     #pragma hdrstop
 #endif

 #ifndef WX_PRECOMP
     #include "wx/wx.h"
 #endif
 @endcode

 Practically every app should define a new class derived from wxApp.
 By overriding wxApp's OnInit() the program can be initialized,
 e.g. by creating a new main window.

 @code
 class MyApp: public wxApp
 {
     virtual bool OnInit();
 };
 @endcode

 The main window is created by deriving a class from wxFrame and
 giving it a menu and a status bar in its constructor. Also, any class
 that wishes to respond to any "event" (such as mouse clicks or
 messages from the menu or a button) must declare an event table
 using the macro below. 

 Finally, the way to react to such events must be done in "handlers".
 In our sample, we react to two menu items, one for "Quit" and one for
 displaying an "About" window. These handlers should not be virtual.

 @code
 class MyFrame: public wxFrame
 {
 public:
     MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size);

     void OnQuit(wxCommandEvent& event);
     void OnAbout(wxCommandEvent& event);

 private:
     DECLARE_EVENT_TABLE()
 };
 @endcode

 In order to be able to react to a menu command, it must be given a unique
 identifier such as a const or an enum.

 @code
 enum
 {
     ID_Quit = 1,
     ID_About,
 };
 @endcode

 We then proceed to actually implement an event table in which the events
 are routed to their respective handler functions in the class MyFrame.

 There are predefined macros for routing all common events, ranging from
 the selection of a list box entry to a resize event when a user resizes
 a window on the screen. If -1 is given as the ID, the given handler will be
 invoked for any event of the specified type, so that you could add just
 one entry in the event table for all menu commands or all button commands etc.

 The origin of the event can still be distinguished in the event handler as
 the (only) parameter in an event handler is a reference to a wxEvent object,
 which holds various information about the event (such as the ID of and a
 pointer to the class, which emitted the event).

 @code
 BEGIN_EVENT_TABLE(MyFrame, wxFrame)
     EVT_MENU(ID_Quit,  MyFrame::OnQuit)
     EVT_MENU(ID_About, MyFrame::OnAbout)
 END_EVENT_TABLE()
 @endcode

 As in all programs there must be a "main" function. Under wxWidgets main is implemented
 using this macro, which creates an application instance and starts the program.

 @code
 IMPLEMENT_APP(MyApp)
 @endcode

 As mentioned above, wxApp::OnInit() is called upon startup and should be
 used to initialize the program, maybe showing a "splash screen" and creating
 the main window (or several). The frame should get a title bar text ("Hello World")
 and a position and start-up size. One frame can also be declared to be the
 top window. Returning @true indicates a successful initialization.

 @code
 bool MyApp::OnInit()
 {
     MyFrame *frame = new MyFrame( "Hello World", wxPoint(50,50), wxSize(450,340) );
     frame-Show( true );
     SetTopWindow( frame );
     return true;
 }
 @endcode

 In the constructor of the main window (or later on) we create a menu with two menu
 items as well as a status bar to be shown at the bottom of the main window. Both have
 to be "announced" to the frame with respective calls.

 @code
 MyFrame::MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size)
        : wxFrame((wxFrame *)NULL, -1, title, pos, size)
 {
     wxMenu *menuFile = new wxMenu;

     menuFile-Append( ID_About, "" );
     menuFile-AppendSeparator();
     menuFile-Append( ID_Quit, "E" );

     wxMenuBar *menuBar = new wxMenuBar;
     menuBar-Append( menuFile, "" );

     SetMenuBar( menuBar );

     CreateStatusBar();
     SetStatusText( "Welcome to wxWidgets!" );
 }
 @endcode

 Here are the actual event handlers. MyFrame::OnQuit() closes the main window
 by calling Close(). The parameter @true indicates that other windows have no veto
 power such as after asking "Do you really want to close?". If there is no other
 main window left, the application will quit.

 @code
 void MyFrame::OnQuit(wxCommandEvent& WXUNUSED(event))
 {
     Close( true );
 }
 @endcode

 MyFrame::OnAbout() will display a small window with some text in it. In this
 case a typical "About" window with information about the program.

 @code
 void MyFrame::OnAbout(wxCommandEvent& WXUNUSED(event))
 {
     wxMessageBox( "This is a wxWidgets' Hello world sample",
                   "About Hello World", wxOK | wxICON_INFORMATION );
 }
 @endcode

*/