1\section{wxWidgets Hello World sample}\label{helloworld} 2 3As many people have requested a mini-sample to be published here 4so that some quick judgment concerning syntax 5and basic principles can be made, you can now look at wxWidgets' 6"Hello World": 7 8You have to include wxWidgets' header files, of course. This can 9be done on a file by file basis (such as \#include "wx/window.h") 10or using one global include (\#include "wx/wx.h"). This is 11also useful on platforms which support precompiled headers such 12as all major compilers on the Windows platform. 13 14\begin{verbatim} 15// 16// file name: hworld.cpp 17// 18// purpose: wxWidgets "Hello world" 19// 20 21// For compilers that support precompilation, includes "wx/wx.h". 22#include "wx/wxprec.h" 23 24#ifdef __BORLANDC__ 25 #pragma hdrstop 26#endif 27 28#ifndef WX_PRECOMP 29 #include "wx/wx.h" 30#endif 31\end{verbatim} 32 33Practically every app should define a new class derived from wxApp. 34By overriding wxApp's OnInit() the program can be initialized, 35e.g. by creating a new main window. 36 37\begin{verbatim} 38class MyApp: public wxApp 39{ 40 virtual bool OnInit(); 41}; 42\end{verbatim} 43 44The main window is created by deriving a class from wxFrame and 45giving it a menu and a status bar in its constructor. Also, any class 46that wishes to respond to any "event" (such as mouse clicks or 47messages from the menu or a button) must declare an event table 48using the macro below. Finally, the way to react to such events 49must be done in "handlers". In our sample, we react to two menu items, 50one for "Quit" and one for displaying an "About" window. These 51handlers should not be virtual. 52 53\begin{verbatim} 54class MyFrame: public wxFrame 55{ 56public: 57 MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size); 58 59 void OnQuit(wxCommandEvent& event); 60 void OnAbout(wxCommandEvent& event); 61 62private: 63 DECLARE_EVENT_TABLE() 64}; 65\end{verbatim} 66 67In order to be able to react to a menu command, it must be given a unique 68identifier such as a const or an enum. 69 70\begin{verbatim} 71enum 72{ 73 ID_Quit = 1, 74 ID_About, 75}; 76\end{verbatim} 77 78We then proceed to actually implement an event table in which the events 79are routed to their respective handler functions in the class MyFrame. 80There are predefined macros for routing all common events, ranging from 81the selection of a list box entry to a resize event when a user resizes 82a window on the screen. If -1 is given as the ID, the given handler will be 83invoked for any event of the specified type, so that you could add just 84one entry in the event table for all menu commands or all button commands etc. 85The origin of the event can still be distinguished in the event handler as 86the (only) parameter in an event handler is a reference to a wxEvent object, 87which holds various information about the event (such as the ID of and a 88pointer to the class, which emitted the event). 89 90\begin{verbatim} 91BEGIN_EVENT_TABLE(MyFrame, wxFrame) 92 EVT_MENU(ID_Quit, MyFrame::OnQuit) 93 EVT_MENU(ID_About, MyFrame::OnAbout) 94END_EVENT_TABLE() 95\end{verbatim} 96 97As in all programs there must be a "main" function. Under wxWidgets main is implemented 98using this macro, which creates an application instance and starts the program. 99 100\begin{verbatim} 101IMPLEMENT_APP(MyApp) 102\end{verbatim} 103 104As mentioned above, wxApp::OnInit() is called upon startup and should be 105used to initialize the program, maybe showing a "splash screen" and creating 106the main window (or several). The frame should get a title bar text ("Hello World") 107and a position and start-up size. One frame can also be declared to be the 108top window. Returning true indicates a successful initialization. 109 110\begin{verbatim} 111bool MyApp::OnInit() 112{ 113 MyFrame *frame = new MyFrame( "Hello World", wxPoint(50,50), wxSize(450,340) ); 114 frame->Show( true ); 115 SetTopWindow( frame ); 116 return true; 117} 118\end{verbatim} 119 120In the constructor of the main window (or later on) we create a menu with two menu 121items as well as a status bar to be shown at the bottom of the main window. Both have 122to be "announced" to the frame with respective calls. 123 124\begin{verbatim} 125MyFrame::MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size) 126 : wxFrame((wxFrame *)NULL, -1, title, pos, size) 127{ 128 wxMenu *menuFile = new wxMenu; 129 130 menuFile->Append( ID_About, "&About..." ); 131 menuFile->AppendSeparator(); 132 menuFile->Append( ID_Quit, "E&xit" ); 133 134 wxMenuBar *menuBar = new wxMenuBar; 135 menuBar->Append( menuFile, "&File" ); 136 137 SetMenuBar( menuBar ); 138 139 CreateStatusBar(); 140 SetStatusText( "Welcome to wxWidgets!" ); 141} 142\end{verbatim} 143 144Here are the actual event handlers. MyFrame::OnQuit() closes the main window 145by calling Close(). The parameter true indicates that other windows have no veto 146power such as after asking "Do you really want to close?". If there is no other 147main window left, the application will quit. 148 149\begin{verbatim} 150void MyFrame::OnQuit(wxCommandEvent& WXUNUSED(event)) 151{ 152 Close( true ); 153} 154\end{verbatim} 155 156MyFrame::OnAbout() will display a small window with some text in it. In this 157case a typical "About" window with information about the program. 158 159\begin{verbatim} 160void MyFrame::OnAbout(wxCommandEvent& WXUNUSED(event)) 161{ 162 wxMessageBox( "This is a wxWidgets' Hello world sample", 163 "About Hello World", wxOK | wxICON_INFORMATION ); 164} 165\end{verbatim} 166 167