The Frame Constructor

Finally, we have the frame constructor, which implements the frame icon, a menu bar, and a status bar.

#include "mondrian.xpm"

MyFrame::MyFrame(const wxString& title)
       : wxFrame(NULL, wxID_ANY, title)
{
    // Set the frame icon
    SetIcon(wxIcon(mondrian_xpm));

    // Create a menu bar
    wxMenu *fileMenu = new wxMenu;

    // The "About" item should be in the help menu
    wxMenu *helpMenu = new wxMenu;
    helpMenu->Append(wxID_ABOUT, wxT("&About...\tF1"),
                     wxT("Show about dialog"));

    fileMenu->Append(wxID_EXIT, wxT("E&xit\tAlt-X"),
                     wxT("Quit this program"));

    // Now append the freshly created menu to the menu bar...
    wxMenuBar *menuBar = new wxMenuBar();
    menuBar->Append(fileMenu, wxT("&File"));
    menuBar->Append(helpMenu, wxT("&Help"));

    // ... and attach this menu bar to the frame
    SetMenuBar(menuBar);

    // Create a status bar just for fun
    CreateStatusBar(2);
    SetStatusText(wxT("Welcome to wxWidgets!"));
}

This constructor calls the base constructor with the parent window (none, hence NULL ), window identifier, and title. The identifier argument is wxID_ANY, which tells wxWidgets to generate an identifier itself. The base constructor creates the actual window associated with the C++ instanceanother way to achieve this is to call the default constructor of the base class, and then explicitly call wxFrame::Create from within the MyFrame constructor.

Small bitmaps and icons can be implemented using the XPM format on all platforms. XPM files have valid C++ syntax and so can be included as shown previously; the SetIcon line creates an icon on the stack using the C++ variable mondrian_xpm defined in mondrian.xpm , and associates it with the frame.

The menu bar is created next . Menu items are added using the identifier (such as the standard identifier wxID_ABOUT ), the label to be displayed, and a help string to be shown on the status bar. Within each label, a mnemonic letter is marked by a preceding ampersand, and an accelerator is preceded by the tab character ( \t ). A mnemonic is the letter a user presses to highlight a particular item when the menu is displayed. An accelerator is a key combination (such as Alt+X) that can be used to perform that action without showing the menu at all.

The last thing that the constructor does is to create a status bar with two fields at the bottom of the frame and set the first field to the string "Welcome to wxWidgets!"

The Whole Program

It's worth putting together the bits so you can see what the whole program looks like. Normally, you'd have a separate header file and implementation file, but for such a simple program, we can put it all in the same file.

Listing 2-1. The Complete Example

// Name:        minimal.cpp
// Purpose:     Minimal wxWidgets sample
// Author:      Julian Smart

#include "wx/wx.h"

// Declare the application class
class MyApp : public wxApp
{
public:
    // Called on application startup
    virtual bool OnInit();
};

// Declare our main frame class
class MyFrame : public wxFrame
{
public:
    // Constructor
    MyFrame(const wxString& title);

    // Event handlers
    void OnQuit(wxCommandEvent& event);
    void OnAbout(wxCommandEvent& event);

private:
    // This class handles events
    DECLARE_EVENT_TABLE()
};

// Implements MyApp& GetApp()
DECLARE_APP(MyApp)

// Give wxWidgets the means to create a MyApp object
IMPLEMENT_APP(MyApp)

// Initialize the application
bool MyApp::OnInit()
{
    // Create the main application window
    MyFrame *frame = new MyFrame(wxT("Minimal wxWidgets App"));

    // Show it
    frame->Show(true);

    // Start the event loop
    return true;
}

// Event table for MyFrame
BEGIN_EVENT_TABLE(MyFrame, wxFrame)
    EVT_MENU(wxID_ABOUT, MyFrame::OnAbout)
    EVT_MENU(wxID_EXIT,  MyFrame::OnQuit)
END_EVENT_TABLE()

void MyFrame::OnAbout(wxCommandEvent& event)
{
    wxString msg;
    msg.Printf(wxT("Hello and welcome to %s"),
               wxVERSION_STRING);


    wxMessageBox(msg, wxT("About Minimal"),
                 wxOK  wxICON_INFORMATION, this);
}

void MyFrame::OnQuit(wxCommandEvent& event)
{
    // Destroy the frame
    Close();
}

#include "mondrian.xpm"

MyFrame::MyFrame(const wxString& title)
       : wxFrame(NULL, wxID_ANY, title)
{
    // Set the frame icon
    SetIcon(wxIcon(mondrian_xpm));

    // Create a menu bar
    wxMenu *fileMenu = new wxMenu;

    // The "About" item should be in the help menu
    wxMenu *helpMenu = new wxMenu;
    helpMenu->Append(wxID_ABOUT, wxT("&About...\tF1"),
                     wxT("Show about dialog"));

    fileMenu->Append(wxID_EXIT, wxT("E&xit\tAlt-X"),
                     wxT("Quit this program"));

    // Now append the freshly created menu to the menu bar...
    wxMenuBar *menuBar = new wxMenuBar();
    menuBar->Append(fileMenu, wxT("&File"));
    menuBar->Append(helpMenu, wxT("&Help"));

    // ... and attach this menu bar to the frame
    SetMenuBar(menuBar);

    // Create a status bar just for fun
    CreateStatusBar(2);
    SetStatusText(wxT("Welcome to wxWidgets!"));
}