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# A Complete Canvas Application

This is a complete example program with a main window, menus and toolbars. The main widget is a QCanvas, and this example demonstrates basic canvas usage.

Project file:

    TEMPLATE = app
    CONFIG  += warn_on

    HEADERS +=  element.h \
                canvastext.h \
                canvasview.h \
                chartform.h \
                optionsform.h \
                setdataform.h
    SOURCES +=  element.cpp \
                canvasview.cpp \
                chartform.cpp \
                chartform_canvas.cpp \
                chartform_files.cpp \
                optionsform.cpp \
                setdataform.cpp \
                main.cpp

Header files:

    #ifndef ELEMENT_H
    #define ELEMENT_H

    #include <qcolor.h>
    #include <qnamespace.h>
    #include <qstring.h>
    #include <qvaluevector.h>

    class Element;

    typedef QValueVector<Element> ElementVector;

    /*
        Elements are valid if they have a value which is > EPSILON.
    */
    const double EPSILON = 0.0000001; // Must be > INVALID.

    class Element
    {
    public:
        enum { INVALID = -1 };
        enum { NO_PROPORTION = -1 };
        enum { MAX_PROPOINTS = 3 }; // One proportional point per chart type

        Element( double value = INVALID, QColor valueColor = Qt::gray,
                 int valuePattern = Qt::SolidPattern,
                 const QString& label = QString::null,
                 QColor labelColor = Qt::black ) {
            init( value, valueColor, valuePattern, label, labelColor );
            for ( int i = 0; i < MAX_PROPOINTS * 2; ++i )
                m_propoints[i] = NO_PROPORTION;
        }
        ~Element() {}

        bool isValid() const { return m_value > EPSILON; }

        double value() const { return m_value; }
        QColor valueColor() const { return m_valueColor; }
        int valuePattern() const { return m_valuePattern; }
        QString label() const { return m_label; }
        QColor labelColor() const { return m_labelColor; }
        double proX( int index ) const;
        double proY( int index ) const;

        void set( double value = INVALID, QColor valueColor = Qt::gray,
                  int valuePattern = Qt::SolidPattern,
                  const QString& label = QString::null,
                  QColor labelColor = Qt::black ) {
            init( value, valueColor, valuePattern, label, labelColor );
        }
        void setValue( double value ) { m_value = value; }
        void setValueColor( QColor valueColor ) { m_valueColor = valueColor; }
        void setValuePattern( int valuePattern );
        void setLabel( const QString& label ) { m_label = label; }
        void setLabelColor( QColor labelColor ) { m_labelColor = labelColor; }
        void setProX( int index, double value );
        void setProY( int index, double value );

    private:
        void init( double value, QColor valueColor, int valuePattern,
                   const QString& label, QColor labelColor );

        double m_value;
        QColor m_valueColor;
        int m_valuePattern;
        QString m_label;
        QColor m_labelColor;
        double m_propoints[2 * MAX_PROPOINTS];
    };

    Q_EXPORT QTextStream &operator<<( QTextStream&, const Element& );
    Q_EXPORT QTextStream &operator>>( QTextStream&, Element& );

    #endif

    #ifndef CHARTFORM_H
    #define CHARTFORM_H

    #include "element.h"

    #include <qmainwindow.h>
    #include <qstringlist.h>

    class CanvasView;

    class QAction;
    class QCanvas;
    class QFont;
    class QPrinter;
    class QString;

    class ChartForm: public QMainWindow
    {
        Q_OBJECT
    public:
        enum { MAX_ELEMENTS = 100 };
        enum { MAX_RECENTFILES = 9 }; // Must not exceed 9
        enum ChartType { PIE, VERTICAL_BAR, HORIZONTAL_BAR };
        enum AddValuesType { NO, YES, AS_PERCENTAGE };

        ChartForm( const QString& filename );
        ~ChartForm();

        int chartType() { return m_chartType; }
        void setChanged( bool changed = true ) { m_changed = changed; }
        void drawElements();

        QPopupMenu *optionsMenu; // Why public? See canvasview.cpp

    private slots:
        void fileNew();
        void fileOpen();
        void fileOpenRecent( int index );
        void fileSave();
        void fileSaveAs();
        void fileSaveAsPixmap();
        void filePrint();
        void fileQuit();
        void optionsSetData();
        void updateChartType( QAction *action );
        void optionsSetFont();
        void optionsSetOptions();
        void helpHelp();
        void helpAbout();
        void helpAboutQt();
        void saveOptions();

    private:
        void init();
        void load( const QString& filename );
        bool okToClear();
        void drawPieChart( const double scales[], double total, int count );
        void drawVerticalBarChart( const double scales[], double total, int count );
        void drawHorizontalBarChart( const double scales[], double total, int count );

        QString valueLabel( const QString& label, double value, double total );
        void updateRecentFiles( const QString& filename );
        void updateRecentFilesMenu();
        void setChartType( ChartType chartType );

        QPopupMenu *fileMenu;
        QAction *optionsPieChartAction;
        QAction *optionsHorizontalBarChartAction;
        QAction *optionsVerticalBarChartAction;

        QString m_filename;
        QStringList m_recentFiles;
        QCanvas *m_canvas;
        CanvasView *m_canvasView;
        bool m_changed;
        ElementVector m_elements;
        QPrinter *m_printer;
        ChartType m_chartType;
        AddValuesType m_addValues;
        int m_decimalPlaces;
        QFont m_font;
    };

    #endif

Implementation:

    #include "canvasview.h"
    #include "chartform.h"
    #include "optionsform.h"
    #include "setdataform.h"

    #include <qaction.h>
    #include <qapplication.h>
    #include <qcombobox.h>
    #include <qfile.h>
    #include <qfiledialog.h>
    #include <qfont.h>
    #include <qfontdialog.h>
    #include <qmenubar.h>
    #include <qmessagebox.h>
    #include <qpixmap.h>
    #include <qpopupmenu.h>
    #include <qprinter.h>
    #include <qradiobutton.h>
    #include <qsettings.h>
    #include <qspinbox.h>
    #include <qstatusbar.h>
    #include <qtoolbar.h>
    #include <qtoolbutton.h>

    #include "images/file_new.xpm"
    #include "images/file_open.xpm"
    #include "images/file_save.xpm"
    #include "images/file_print.xpm"
    #include "images/options_setdata.xpm"
    #include "images/options_setfont.xpm"
    #include "images/options_setoptions.xpm"
    #include "images/options_horizontalbarchart.xpm"
    #include "images/options_piechart.xpm"
    #include "images/options_verticalbarchart.xpm"

    const QString WINDOWS_REGISTRY = "/QtExamples";
    const QString APP_KEY = "/Chart/";

    ChartForm::ChartForm( const QString& filename )
        : QMainWindow( 0, 0, WDestructiveClose )
    {
        setIcon( QPixmap( options_piechart ) );

        QAction *fileNewAction;
        QAction *fileOpenAction;
        QAction *fileSaveAction;
        QAction *fileSaveAsAction;
        QAction *fileSaveAsPixmapAction;
        QAction *filePrintAction;
        QAction *fileQuitAction;
        QAction *optionsSetDataAction;
        QAction *optionsSetFontAction;
        QAction *optionsSetOptionsAction;

        fileNewAction = new QAction(
                "New Chart", QPixmap( file_new ),
                "&New", CTRL+Key_N, this, "new" );
        connect( fileNewAction, SIGNAL( activated() ), this, SLOT( fileNew() ) );

        fileOpenAction = new QAction(
                "Open Chart", QPixmap( file_open ),
                "&Open...", CTRL+Key_O, this, "open" );
        connect( fileOpenAction, SIGNAL( activated() ), this, SLOT( fileOpen() ) );

        fileSaveAction = new QAction(
                "Save Chart", QPixmap( file_save ),
                "&Save", CTRL+Key_S, this, "save" );
        connect( fileSaveAction, SIGNAL( activated() ), this, SLOT( fileSave() ) );

        fileSaveAsAction = new QAction(
                "Save Chart As", QPixmap( file_save ),
                "Save &As...", 0, this, "save as" );
        connect( fileSaveAsAction, SIGNAL( activated() ),
                 this, SLOT( fileSaveAs() ) );

        fileSaveAsPixmapAction = new QAction(
                "Save Chart As Bitmap", QPixmap( file_save ),
                "Save As &Bitmap...", CTRL+Key_B, this, "save as bitmap" );
        connect( fileSaveAsPixmapAction, SIGNAL( activated() ),
                 this, SLOT( fileSaveAsPixmap() ) );

        filePrintAction = new QAction(
                "Print Chart", QPixmap( file_print ),
                "&Print Chart...", CTRL+Key_P, this, "print chart" );
        connect( filePrintAction, SIGNAL( activated() ),
                 this, SLOT( filePrint() ) );

        optionsSetDataAction = new QAction(
                "Set Data", QPixmap( options_setdata ),
                "Set &Data...", CTRL+Key_D, this, "set data" );
        connect( optionsSetDataAction, SIGNAL( activated() ),
                 this, SLOT( optionsSetData() ) );

        QActionGroup *chartGroup = new QActionGroup( this ); // Connected later
        chartGroup->setExclusive( true );

        optionsPieChartAction = new QAction(
                "Pie Chart", QPixmap( options_piechart ),
                "&Pie Chart", CTRL+Key_I, chartGroup, "pie chart" );
        optionsPieChartAction->setToggleAction( true );

        optionsHorizontalBarChartAction = new QAction(
                "Horizontal Bar Chart", QPixmap( options_horizontalbarchart ),
                "&Horizontal Bar Chart", CTRL+Key_H, chartGroup,
                "horizontal bar chart" );
        optionsHorizontalBarChartAction->setToggleAction( true );

        optionsVerticalBarChartAction = new QAction(
                "Vertical Bar Chart", QPixmap( options_verticalbarchart ),
                "&Vertical Bar Chart", CTRL+Key_V, chartGroup, "Vertical bar chart" );
        optionsVerticalBarChartAction->setToggleAction( true );

        optionsSetFontAction = new QAction(
                "Set Font", QPixmap( options_setfont ),
                "Set &Font...", CTRL+Key_F, this, "set font" );
        connect( optionsSetFontAction, SIGNAL( activated() ),
                 this, SLOT( optionsSetFont() ) );

        optionsSetOptionsAction = new QAction(
                "Set Options", QPixmap( options_setoptions ),
                "Set &Options...", 0, this, "set options" );
        connect( optionsSetOptionsAction, SIGNAL( activated() ),
                 this, SLOT( optionsSetOptions() ) );

        fileQuitAction = new QAction( "Quit", "&Quit", CTRL+Key_Q, this, "quit" );
        connect( fileQuitAction, SIGNAL( activated() ), this, SLOT( fileQuit() ) );

        QToolBar* fileTools = new QToolBar( this, "file operations" );
        fileTools->setLabel( "File Operations" );
        fileNewAction->addTo( fileTools );
        fileOpenAction->addTo( fileTools );
        fileSaveAction->addTo( fileTools );
        fileTools->addSeparator();
        filePrintAction->addTo( fileTools );

        QToolBar *optionsTools = new QToolBar( this, "options operations" );
        optionsTools->setLabel( "Options Operations" );
        optionsSetDataAction->addTo( optionsTools );
        optionsTools->addSeparator();
        optionsPieChartAction->addTo( optionsTools );
        optionsHorizontalBarChartAction->addTo( optionsTools );
        optionsVerticalBarChartAction->addTo( optionsTools );
        optionsTools->addSeparator();
        optionsSetFontAction->addTo( optionsTools );
        optionsTools->addSeparator();
        optionsSetOptionsAction->addTo( optionsTools );

        fileMenu = new QPopupMenu( this );
        menuBar()->insertItem( "&File", fileMenu );
        fileNewAction->addTo( fileMenu );
        fileOpenAction->addTo( fileMenu );
        fileSaveAction->addTo( fileMenu );
        fileSaveAsAction->addTo( fileMenu );
        fileMenu->insertSeparator();
        fileSaveAsPixmapAction->addTo( fileMenu );
        fileMenu->insertSeparator();
        filePrintAction->addTo( fileMenu );
        fileMenu->insertSeparator();
        fileQuitAction->addTo( fileMenu );
        fileMenu->insertSeparator();

        optionsMenu = new QPopupMenu( this );
        menuBar()->insertItem( "&Options", optionsMenu );
        optionsSetDataAction->addTo( optionsMenu );
        optionsMenu->insertSeparator();
        optionsPieChartAction->addTo( optionsMenu );
        optionsHorizontalBarChartAction->addTo( optionsMenu );
        optionsVerticalBarChartAction->addTo( optionsMenu );
        optionsMenu->insertSeparator();
        optionsSetFontAction->addTo( optionsMenu );
        optionsMenu->insertSeparator();
        optionsSetOptionsAction->addTo( optionsMenu );

        menuBar()->insertSeparator();

        QPopupMenu *helpMenu = new QPopupMenu( this );
        menuBar()->insertItem( "&Help", helpMenu );
        helpMenu->insertItem( "&Help", this, SLOT(helpHelp()), Key_F1 );
        helpMenu->insertItem( "&About", this, SLOT(helpAbout()) );
        helpMenu->insertItem( "About &Qt", this, SLOT(helpAboutQt()) );

        m_printer = 0;
        m_elements.resize( MAX_ELEMENTS );

        QSettings settings;
        settings.insertSearchPath( QSettings::Windows, WINDOWS_REGISTRY );
        int windowWidth = settings.readNumEntry( APP_KEY + "WindowWidth", 460 );
        int windowHeight = settings.readNumEntry( APP_KEY + "WindowHeight", 530 );
        int windowX = settings.readNumEntry( APP_KEY + "WindowX", 0 );
        int windowY = settings.readNumEntry( APP_KEY + "WindowY", 0 );
        setChartType( ChartType(
                settings.readNumEntry( APP_KEY + "ChartType", int(PIE) ) ) );
        m_addValues = AddValuesType(
                        settings.readNumEntry( APP_KEY + "AddValues", int(NO) ));
        m_decimalPlaces = settings.readNumEntry( APP_KEY + "Decimals", 2 );
        m_font = QFont( "Helvetica", 18, QFont::Bold );
        m_font.fromString(
                settings.readEntry( APP_KEY + "Font", m_font.toString() ) );
        for ( int i = 0; i < MAX_RECENTFILES; ++i ) {
            QString filename = settings.readEntry( APP_KEY + "File" +
                                                   QString::number( i + 1 ) );
            if ( !filename.isEmpty() )
                m_recentFiles.push_back( filename );
        }
        if ( m_recentFiles.count() )
            updateRecentFilesMenu();

        // Connect *after* we've set the chart type on so we don't call
        // drawElements() prematurely.
        connect( chartGroup, SIGNAL( selected(QAction*) ),
                 this, SLOT( updateChartType(QAction*) ) );

        resize( windowWidth, windowHeight );
        move( windowX, windowY );

        m_canvas = new QCanvas( this );
        m_canvas->resize( width(), height() );
        m_canvasView = new CanvasView( m_canvas, &m_elements, this );
        setCentralWidget( m_canvasView );
        m_canvasView->show();

        if ( !filename.isEmpty() )
            load( filename );
        else {
            init();
            m_elements[0].set( 20, red,    14, "Red" );
            m_elements[1].set( 70, cyan,    2, "Cyan",   darkGreen );
            m_elements[2].set( 35, blue,   11, "Blue" );
            m_elements[3].set( 55, yellow,  1, "Yellow", darkBlue );
            m_elements[4].set( 80, magenta, 1, "Magenta" );
            drawElements();
        }

        statusBar()->message( "Ready", 2000 );
    }

    ChartForm::~ChartForm()
    {
        delete m_printer;
    }

    void ChartForm::init()
    {
        setCaption( "Chart" );
        m_filename = QString::null;
        m_changed = false;

        m_elements[0]  = Element( Element::INVALID, red );
        m_elements[1]  = Element( Element::INVALID, cyan );
        m_elements[2]  = Element( Element::INVALID, blue );
        m_elements[3]  = Element( Element::INVALID, yellow );
        m_elements[4]  = Element( Element::INVALID, green );
        m_elements[5]  = Element( Element::INVALID, magenta );
        m_elements[6]  = Element( Element::INVALID, darkYellow );
        m_elements[7]  = Element( Element::INVALID, darkRed );
        m_elements[8]  = Element( Element::INVALID, darkCyan );
        m_elements[9]  = Element( Element::INVALID, darkGreen );
        m_elements[10] = Element( Element::INVALID, darkMagenta );
        m_elements[11] = Element( Element::INVALID, darkBlue );
        for ( int i = 12; i < MAX_ELEMENTS; ++i ) {
            double x = (double(i) / MAX_ELEMENTS) * 360;
            int y = (int(x * 256) % 105) + 151;
            int z = ((i * 17) % 105) + 151;
            m_elements[i] = Element( Element::INVALID, QColor( int(x), y, z, QColor::Hsv ) );
        }
    }

    void ChartForm::fileNew()
    {
        if ( okToClear() ) {
            init();
            drawElements();
        }
    }

    void ChartForm::fileOpen()
    {
        if ( !okToClear() )
            return;

        QString filename = QFileDialog::getOpenFileName(
                                QString::null, "Charts (*.cht)", this,
                                "file open", "Chart -- File Open" );
        if ( !filename.isEmpty() )
            load( filename );
        else
            statusBar()->message( "File Open abandoned", 2000 );
    }

    void ChartForm::fileSaveAs()
    {
        QString filename = QFileDialog::getSaveFileName(
                                QString::null, "Charts (*.cht)", this,
                                "file save as", "Chart -- File Save As" );
        if ( !filename.isEmpty() ) {
            int answer = 0;
            if ( QFile::exists( filename ) )
                answer = QMessageBox::warning(
                                this, "Chart -- Overwrite File",
                                QString( "Overwrite\n\'%1\'?" ).
                                    arg( filename ),
                                "&Yes", "&No", QString::null, 1, 1 );
            if ( answer == 0 ) {
                m_filename = filename;
                updateRecentFiles( filename );
                fileSave();
                return;
            }
        }
        statusBar()->message( "Saving abandoned", 2000 );
    }

    void ChartForm::fileOpenRecent( int index )
    {
        if ( !okToClear() )
            return;

        load( m_recentFiles[index] );
    }

    void ChartForm::updateRecentFiles( const QString& filename )
    {
        if ( m_recentFiles.find( filename ) != m_recentFiles.end() )
            return;

        m_recentFiles.push_back( filename );
        if ( m_recentFiles.count() > MAX_RECENTFILES )
            m_recentFiles.pop_front();

        updateRecentFilesMenu();
    }

    void ChartForm::updateRecentFilesMenu()
    {
        for ( int i = 0; i < MAX_RECENTFILES; ++i ) {
            if ( fileMenu->findItem( i ) )
                fileMenu->removeItem( i );
            if ( i < int(m_recentFiles.count()) )
                fileMenu->insertItem( QString( "&%1 %2" ).
                                        arg( i + 1 ).arg( m_recentFiles[i] ),
                                      this, SLOT( fileOpenRecent(int) ),
                                      0, i );
        }
    }

    void ChartForm::fileQuit()
    {
        if ( okToClear() ) {
            saveOptions();
            qApp->exit( 0 );
        }
    }

    bool ChartForm::okToClear()
    {
        if ( m_changed ) {
            QString msg;
            if ( m_filename.isEmpty() )
                msg = "Unnamed chart ";
            else
                msg = QString( "Chart '%1'\n" ).arg( m_filename );
            msg += "has been changed.";
            switch( QMessageBox::information( this, "Chart -- Unsaved Changes",
                                              msg, "&Save", "Cancel", "&Abandon",
                                              0, 1 ) ) {
                case 0:
                    fileSave();
                    break;
                case 1:
                default:
                    return false;
                    break;
                case 2:
                    break;
            }
        }

        return true;
    }

    void ChartForm::saveOptions()
    {
        QSettings settings;
        settings.insertSearchPath( QSettings::Windows, WINDOWS_REGISTRY );
        settings.writeEntry( APP_KEY + "WindowWidth", width() );
        settings.writeEntry( APP_KEY + "WindowHeight", height() );
        settings.writeEntry( APP_KEY + "WindowX", x() );
        settings.writeEntry( APP_KEY + "WindowY", y() );
        settings.writeEntry( APP_KEY + "ChartType", int(m_chartType) );
        settings.writeEntry( APP_KEY + "AddValues", int(m_addValues) );
        settings.writeEntry( APP_KEY + "Decimals", m_decimalPlaces );
        settings.writeEntry( APP_KEY + "Font", m_font.toString() );
        for ( int i = 0; i < int(m_recentFiles.count()); ++i )
            settings.writeEntry( APP_KEY + "File" + QString::number( i + 1 ),
                                 m_recentFiles[i] );
    }

    void ChartForm::optionsSetData()
    {
        SetDataForm *setDataForm = new SetDataForm( &m_elements, m_decimalPlaces, this );
        if ( setDataForm->exec() ) {
            m_changed = true;
            drawElements();
        }
        delete setDataForm;
    }

    void ChartForm::setChartType( ChartType chartType )
    {
        m_chartType = chartType;
        switch ( m_chartType ) {
            case PIE:
                optionsPieChartAction->setOn( true );
                break;
            case VERTICAL_BAR:
                optionsVerticalBarChartAction->setOn( true );
                break;
            case HORIZONTAL_BAR:
                optionsHorizontalBarChartAction->setOn( true );
                break;
        }
    }

    void ChartForm::updateChartType( QAction *action )
    {
        if ( action == optionsPieChartAction ) {
            m_chartType = PIE;
        }
        else if ( action == optionsHorizontalBarChartAction ) {
            m_chartType = HORIZONTAL_BAR;
        }
        else if ( action == optionsVerticalBarChartAction ) {
            m_chartType = VERTICAL_BAR;
        }

        drawElements();
    }

    void ChartForm::optionsSetFont()
    {
        bool ok;
        QFont font = QFontDialog::getFont( &ok, m_font, this );
        if ( ok ) {
            m_font = font;
            drawElements();
        }
    }

    void ChartForm::optionsSetOptions()
    {
        OptionsForm *optionsForm = new OptionsForm( this );
        optionsForm->chartTypeComboBox->setCurrentItem( m_chartType );
        optionsForm->setFont( m_font );
        switch ( m_addValues ) {
            case NO:
                optionsForm->noRadioButton->setChecked( true );
                break;
            case YES:
                optionsForm->yesRadioButton->setChecked( true );
                break;
            case AS_PERCENTAGE:
                optionsForm->asPercentageRadioButton->setChecked( true );
                break;
        }
        optionsForm->decimalPlacesSpinBox->setValue( m_decimalPlaces );
        if ( optionsForm->exec() ) {
            setChartType( ChartType(
                    optionsForm->chartTypeComboBox->currentItem()) );
            m_font = optionsForm->font();
            if ( optionsForm->noRadioButton->isChecked() )
                m_addValues = NO;
            else if ( optionsForm->yesRadioButton->isChecked() )
                m_addValues = YES;
            else if ( optionsForm->asPercentageRadioButton->isChecked() )
                m_addValues = AS_PERCENTAGE;
            m_decimalPlaces = optionsForm->decimalPlacesSpinBox->value();
            drawElements();
        }
        delete optionsForm;
    }

    void ChartForm::helpHelp()
    {
        statusBar()->message( "Help is not implemented yet", 2000 );
    }

    void ChartForm::helpAbout()
    {
        QMessageBox::about( this, "Chart -- About",
                            "<center><h1><font color=blue>Chart<font></h1></center>"
                            "<p>Chart your data with <i>chart</i>.</p>"
                            );
    }

    void ChartForm::helpAboutQt()
    {
        QMessageBox::aboutQt( this, "Chart -- About Qt" );
    }

Main:

    #include <qapplication.h>
    #include "chartform.h"

    int main( int argc, char *argv[] )
    {
        QApplication app( argc, argv );

        QString filename;
        if ( app.argc() > 1 ) {
            filename = app.argv()[1];
            if ( !filename.endsWith( ".cht" ) )
                filename = QString::null;
        }

        ChartForm *cf = new ChartForm( filename );
        app.setMainWidget( cf );
        cf->show();
        app.connect( &app, SIGNAL(lastWindowClosed()), cf, SLOT(fileQuit()) );

        return app.exec();
    }

See also Step-by-step Examples.