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# How to create a large, sparse QTable

This example shows a sparse table implementation using a QIntDict to keep track of the cells that are actually in use.

Implementation:

    /****************************************************************************
    ** $Id: qt/main.cpp   3.3.8   edited Jan 11 14:37 $
    **
    ** Copyright (C) 1992-2007 Trolltech ASA.  All rights reserved.
    **
    ** This file is part of an example program for Qt.  This example
    ** program may be used, distributed and modified without limitation.
    **
    *****************************************************************************/

    #include <qapplication.h>
    #include <qtable.h>

    // Table size

    const int numRows = 1000000;
    const int numCols = 1000000;

    class MyTable : public QTable
    {
    public:
        MyTable( int r, int c ) : QTable( r, c ) {
            items.setAutoDelete( TRUE );
            widgets.setAutoDelete( TRUE );
            setCaption( tr( "A 1 Million x 1 Million Cell Table" ) );
            setLeftMargin( fontMetrics().width( "W999999W" ) );
        }

        void resizeData( int ) {}
        QTableItem *item( int r, int c ) const { return items.find( indexOf( r, c ) ); }
        void setItem( int r, int c, QTableItem *i ) { items.replace( indexOf( r, c ), i ); }
        void clearCell( int r, int c ) { items.remove( indexOf( r, c ) ); }
        void takeItem( QTableItem *item )
        {
            items.setAutoDelete( FALSE );
            items.remove( indexOf( item->row(), item->col() ) );
            items.setAutoDelete( TRUE );
        }
        void insertWidget( int r, int c, QWidget *w ) { widgets.replace( indexOf( r, c ), w );  }
        QWidget *cellWidget( int r, int c ) const { return widgets.find( indexOf( r, c ) ); }
        void clearCellWidget( int r, int c )
        {
            QWidget *w = widgets.take( indexOf( r, c ) );
            if ( w )
                w->deleteLater();
        }

    private:
        QIntDict<QTableItem> items;
        QIntDict<QWidget> widgets;

    };

    // The program starts here.

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

        MyTable table( numRows, numCols );
        app.setMainWidget( &table );
        table.show();
        return app.exec();
    }

See also Table Examples.