291 lines
8.7 KiB
C
291 lines
8.7 KiB
C
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/////////////////////////////////////////////////////////////////////////////
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// Name: helloworld.h
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// Purpose: topic overview
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// Author: wxWidgets team
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// Licence: wxWindows licence
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/////////////////////////////////////////////////////////////////////////////
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/**
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@page overview_helloworld Hello World Example
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@tableofcontents
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This page shows a very simple wxWidgets program that can be used as a skeleton
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for your own code. While it does nothing very useful, it introduces a couple of
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important concepts and explains how to write a working wxWidgets application.
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First, you have to include wxWidgets' header files, of course. This can be done
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on a file by file basis (such as @c wx/window.h) or using one global include
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(@c wx/wx.h) which includes most of the commonly needed headers (although not
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all of them as there are simply too many wxWidgets headers to pull in all of
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them). For the platforms with support for precompiled headers, as indicated by
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@c WX_PRECOMP, this global header is already included by @c wx/wxprec.h so we
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only include it for the other ones:
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@code
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// wxWidgets "Hello world" Program
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// For compilers that support precompilation, includes "wx/wx.h".
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#include <wx/wxprec.h>
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#ifndef WX_PRECOMP
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#include <wx/wx.h>
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#endif
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@endcode
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Practically every app should define a new class derived from wxApp. By
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overriding wxApp's OnInit() virtual method the program can be initialized, e.g.
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by creating a new main window.
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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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virtual bool OnInit();
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};
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@endcode
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The main window is created by deriving a class from wxFrame and giving it a
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menu and a status bar in its constructor. Also, any class that wishes to
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respond to any "event" (such as mouse clicks or messages from the menu or a
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button) must declare an event table using the macro below.
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Finally, the way to react to such events must be done in "handlers". In our
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sample, we react to three menu items, one for our custom menu command and two
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for the standard "Exit" and "About" commands (any program should normally
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implement the latter two). Notice that these handlers don't need to be neither
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virtual nor public.
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@code
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class MyFrame: public wxFrame
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{
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public:
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MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size);
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private:
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void OnHello(wxCommandEvent& event);
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void OnExit(wxCommandEvent& event);
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void OnAbout(wxCommandEvent& event);
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wxDECLARE_EVENT_TABLE();
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};
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@endcode
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In order to be able to react to a menu command, it must be given a unique
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identifier which can be defined as a const variable or an enum element. The
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latter is often used because typically many such constants will be needed:
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@code
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enum
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{
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ID_Hello = 1
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};
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@endcode
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Notice that you don't need to define identifiers for the "About" and "Exit". We
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then proceed to actually implement an event table in which the events are
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routed to their respective handler functions in the class MyFrame.
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There are predefined macros for routing all common events, ranging from the
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selection of a list box entry to a resize event when a user resizes a window on
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the screen. If @c wxID_ANY is given as the ID, the given handler will be
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invoked for any event of the specified type, so that you could add just one
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entry in the event table for all menu commands or all button commands etc.
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The origin of the event can still be distinguished in the event handler as the
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(only) parameter in an event handler is a reference to a wxEvent object, which
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holds various information about the event (such as the ID of and a pointer to
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the class, which emitted the event).
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@code
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wxBEGIN_EVENT_TABLE(MyFrame, wxFrame)
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EVT_MENU(ID_Hello, MyFrame::OnHello)
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EVT_MENU(wxID_EXIT, MyFrame::OnExit)
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EVT_MENU(wxID_ABOUT, MyFrame::OnAbout)
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wxEND_EVENT_TABLE()
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@endcode
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As in all programs there must be a "main" function. Under wxWidgets main is
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implemented using this macro, which creates an application instance and starts
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the program.
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@code
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wxIMPLEMENT_APP(MyApp)
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@endcode
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As mentioned above, wxApp::OnInit() is called upon startup and should be used
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to initialize the program, maybe showing a "splash screen" and creating the
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main window (or several). The frame should get a title bar text ("Hello World")
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and a position and start-up size. One frame can also be declared to be the top
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window. Returning @true indicates a successful initialization.
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@code
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bool MyApp::OnInit()
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{
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MyFrame *frame = new MyFrame( "Hello World", wxPoint(50, 50), wxSize(450, 340) );
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frame->Show( true );
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return true;
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}
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@endcode
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In the constructor of the main window (or later on) we create a menu with our
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menu items as well as a status bar to be shown at the bottom of the main
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window. Both have to be associated with the frame with respective calls.
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@code
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MyFrame::MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size)
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: wxFrame(NULL, wxID_ANY, title, pos, size)
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{
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wxMenu *menuFile = new wxMenu;
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menuFile->Append(ID_Hello, "&Hello...\tCtrl-H",
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"Help string shown in status bar for this menu item");
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menuFile->AppendSeparator();
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menuFile->Append(wxID_EXIT);
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wxMenu *menuHelp = new wxMenu;
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menuHelp->Append(wxID_ABOUT);
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wxMenuBar *menuBar = new wxMenuBar;
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menuBar->Append( menuFile, "&File" );
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menuBar->Append( menuHelp, "&Help" );
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SetMenuBar( menuBar );
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CreateStatusBar();
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SetStatusText( "Welcome to wxWidgets!" );
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}
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@endcode
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Notice that we don't need to specify the labels for the standard menu items
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@c wxID_ABOUT and @c wxID_EXIT, they will be given standard (even correctly
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translated) labels and also standard accelerators correct for the current
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platform making your program behaviour more native. For this reason you should
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prefer reusing the standard ids (see @ref page_stockitems) if possible.
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Here are the standard event handlers implementations. MyFrame::OnExit() closes
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the main window by calling Close(). The parameter @true indicates that other
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windows have no veto power such as after asking "Do you really want to close?".
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If there is no other main window left, the application will quit.
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@code
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void MyFrame::OnExit(wxCommandEvent& event)
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{
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Close( true );
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}
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@endcode
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MyFrame::OnAbout() will display a small window with some text in it. In this
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case a typical "About" window with information about the program.
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@code
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void MyFrame::OnAbout(wxCommandEvent& event)
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{
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wxMessageBox( "This is a wxWidgets' Hello world sample",
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"About Hello World", wxOK | wxICON_INFORMATION );
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}
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@endcode
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The implementation of custom menu command handler may perform whatever task
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your program needs to do, in this case we will simply show a message from it as
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befits a hello world example:
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@code
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void MyFrame::OnHello(wxCommandEvent& event)
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{
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wxLogMessage("Hello world from wxWidgets!");
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}
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@endcode
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Here is the entire program that can be copied and pasted:
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@code
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// wxWidgets "Hello world" Program
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// For compilers that support precompilation, includes "wx/wx.h".
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#include <wx/wxprec.h>
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#ifndef WX_PRECOMP
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#include <wx/wx.h>
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#endif
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class MyApp: 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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class MyFrame: public wxFrame
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{
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public:
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MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size);
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private:
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void OnHello(wxCommandEvent& event);
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void OnExit(wxCommandEvent& event);
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void OnAbout(wxCommandEvent& event);
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wxDECLARE_EVENT_TABLE();
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};
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enum
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{
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ID_Hello = 1
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};
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wxBEGIN_EVENT_TABLE(MyFrame, wxFrame)
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EVT_MENU(ID_Hello, MyFrame::OnHello)
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EVT_MENU(wxID_EXIT, MyFrame::OnExit)
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EVT_MENU(wxID_ABOUT, MyFrame::OnAbout)
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wxEND_EVENT_TABLE()
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wxIMPLEMENT_APP(MyApp);
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bool MyApp::OnInit()
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{
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MyFrame *frame = new MyFrame( "Hello World", wxPoint(50, 50), wxSize(450, 340) );
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frame->Show( true );
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return true;
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}
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MyFrame::MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size)
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: wxFrame(NULL, wxID_ANY, title, pos, size)
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{
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wxMenu *menuFile = new wxMenu;
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menuFile->Append(ID_Hello, "&Hello...\tCtrl-H",
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"Help string shown in status bar for this menu item");
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menuFile->AppendSeparator();
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menuFile->Append(wxID_EXIT);
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wxMenu *menuHelp = new wxMenu;
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menuHelp->Append(wxID_ABOUT);
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wxMenuBar *menuBar = new wxMenuBar;
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menuBar->Append( menuFile, "&File" );
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menuBar->Append( menuHelp, "&Help" );
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SetMenuBar( menuBar );
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CreateStatusBar();
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SetStatusText( "Welcome to wxWidgets!" );
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}
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void MyFrame::OnExit(wxCommandEvent& event)
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{
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Close( true );
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}
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void MyFrame::OnAbout(wxCommandEvent& event)
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{
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wxMessageBox( "This is a wxWidgets' Hello world sample",
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"About Hello World", wxOK | wxICON_INFORMATION );
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}
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void MyFrame::OnHello(wxCommandEvent& event)
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{
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wxLogMessage("Hello world from wxWidgets!");
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}
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@endcode
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*/
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