Question

This example shows how to use Qt's scrollview. This is a widget optimized for very large contents.

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Implementation:

/****************************************************************************
** $Id:  qt/scrollview.cpp   3.0.5   edited Oct 15 2001 $
**
** Copyright (C) 1992-2000 Trolltech AS.  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 <qscrollview.h>
#include <qapplication.h>
#include <qmenubar.h>
#include <qpopupmenu.h>
#include <qpushbutton.h>
#include <qpainter.h>
#include <qpixmap.h>
#include <qmessagebox.h>
#include <qlayout.h>
#include <qlabel.h>
#include <qmultilineedit.h>
#include <qsizegrip.h>
#include <stdlib.h>


static const int style_id       = 0x1000;
static const int lw_id          = 0x2000;
static const int mlw_id         = 0x4000;
static const int mw_id          = 0x8000;
static const int max_lw         = 16;
static const int max_mlw        = 5;
static const int max_mw         = 10;


class BigShrinker : public QFrame {
    Q_OBJECT
public:
    BigShrinker(QWidget* parent) :
        QFrame(parent)
    {
        setFrameStyle(QFrame::Box|QFrame::Sunken);
        int h=35;
        int b=0;
        for (int y=0; y<2000-h; y+=h+10) {
            if (y == 0) {
                QButton* q=new QPushButton("Quit", this);
                connect(q, SIGNAL(clicked()), qApp, SLOT(quit()));
            } else {
                QString str;
                if ( b > 0 ) {
                    str.sprintf("Button %d", b++);
                } else {
                    str = "I'm shrinking!";
                    ++b;
                }
                (new QPushButton(str, this))->move(y/2,y);
            }
        }
        resize(1000,2000);

        startTimer(250);
    }

    void timerEvent(QTimerEvent*)
    {
        int w=width();
        int h=height();
        if ( w > 50 ) w -= 1;
        if ( h > 50 ) h -= 2;
        resize(w,h);
    }

    void mouseReleaseEvent(QMouseEvent* e)
    {
        emit clicked(e->x(), e->y());
    }

signals:
    void clicked(int,int);
};

class BigMatrix : public QScrollView {
    QMultiLineEdit *dragging;
public:
    BigMatrix(QWidget* parent) :
        QScrollView(parent,"matrix", WStaticContents),
        bg("bg.ppm")
    {
        bg.load("bg.ppm");
        resizeContents(400000,300000);

        dragging = 0;
    }

    void viewportMousePressEvent(QMouseEvent* e)
    {
        int x, y;
        viewportToContents( e->x(),  e->y(), x, y );
        dragging = new QMultiLineEdit(viewport(),"Another");
        dragging->setText("Thanks!");
        dragging->resize(100,100);
        addChild(dragging, x, y);
        showChild(dragging);
    }

    void viewportMouseReleaseEvent(QMouseEvent*)
    {
        dragging = 0;
    }

    void viewportMouseMoveEvent(QMouseEvent* e)
    {
        if ( dragging ) {
            int mx, my;
            viewportToContents( e->x(),  e->y(), mx, my );
            int cx = childX(dragging);
            int cy = childY(dragging);
            int w = mx - cx + 1;
            int h = my - cy + 1;
            QString msg;
            msg.sprintf("at (%d,%d) %d by %d",cx,cy,w,h);
            dragging->setText(msg);
            dragging->resize(w,h);
        }
    }

protected:
    void drawContents(QPainter* p, int cx, int cy, int cw, int ch)
    {
        // The Background
        if ( !bg.isNull() ) {
            int rowheight=bg.height();
            int toprow=cy/rowheight;
            int bottomrow=(cy+ch+rowheight-1)/rowheight;
            int colwidth=bg.width();
            int leftcol=cx/colwidth;
            int rightcol=(cx+cw+colwidth-1)/colwidth;
            for (int r=toprow; r<=bottomrow; r++) {
                int py=r*rowheight;
                for (int c=leftcol; c<=rightcol; c++) {
                    int px=c*colwidth;
                    p->drawPixmap(px, py, bg);
                }
            }
        } else {
            p->fillRect(cx, cy, cw, ch, QColor(240,222,208));
        }

        // The Numbers
        {
            QFontMetrics fm=p->fontMetrics();
            int rowheight=fm.lineSpacing();
            int toprow=cy/rowheight;
            int bottomrow=(cy+ch+rowheight-1)/rowheight;
            int colwidth=fm.width("00000,000000 ")+3;
            int leftcol=cx/colwidth;
            int rightcol=(cx+cw+colwidth-1)/colwidth;
            QString str;
            for (int r=toprow; r<=bottomrow; r++) {
                int py=r*rowheight;
                for (int c=leftcol; c<=rightcol; c++) {
                    int px=c*colwidth;
                    str.sprintf("%d,%d",c,r);
                    p->drawText(px+3, py+fm.ascent(), str);
                }
            }

            // The Big Hint
            if (leftcol<10 && toprow<5) {
                p->setFont(QFont("Charter",30));
                p->setPen(red);
                QString text;
                text.sprintf("HINT:  Look at %d,%d",215000/colwidth,115000/rowheight);
                p->drawText(100,50,text);
            }
        }

        // The Big X
        {
            if (cx+cw>200000 && cy+ch>100000 && cx<230000 && cy<130000) {
                // Note that some X server cannot even handle co-ordinates
                // beyond about 4000, so you might not see this.
                p->drawLine(200000,100000,229999,129999);
                p->drawLine(229999,100000,200000,129999);

                // X marks the spot!
                p->setFont(QFont("Charter",100));
                p->setPen(blue);
                p->drawText(215000-500,115000-100,1000,200,AlignCenter,"YOU WIN!!!!!");
            }
        }
    }

private:
    QPixmap bg;
};

class ScrollViewExample : public QWidget {
    Q_OBJECT

public:
    ScrollViewExample(int technique, QWidget* parent=0, const char* name=0) :
        QWidget(parent,name)
    {
        QMenuBar* menubar = new QMenuBar(this);
        Q_CHECK_PTR( menubar );

        QPopupMenu* file = new QPopupMenu( menubar );
        Q_CHECK_PTR( file );
        menubar->insertItem( "&File", file );
        file->insertItem( "Quit", qApp,  SLOT(quit()) );

        vp_options = new QPopupMenu( menubar );
        Q_CHECK_PTR( vp_options );
        vp_options->setCheckable( TRUE );
        menubar->insertItem( "&ScrollView", vp_options );
        connect( vp_options, SIGNAL(activated(int)),
            this, SLOT(doVPMenuItem(int)) );

        vauto_id = vp_options->insertItem( "Vertical Auto" );
        vaoff_id = vp_options->insertItem( "Vertical AlwaysOff" );
        vaon_id = vp_options->insertItem( "Vertical AlwaysOn" );
        vp_options->insertSeparator();
        hauto_id = vp_options->insertItem( "Horizontal Auto" );
        haoff_id = vp_options->insertItem( "Horizontal AlwaysOff" );
        haon_id = vp_options->insertItem( "Horizontal AlwaysOn" );
        vp_options->insertSeparator();
        corn_id = vp_options->insertItem( "cornerWidget" );

        if (technique == 1) {
            vp = new QScrollView(this);
            BigShrinker *bs = new BigShrinker(0);//(vp->viewport());
            vp->addChild(bs);
            bs->setAcceptDrops(TRUE);
            QObject::connect(bs, SIGNAL(clicked(int,int)),
                            vp, SLOT(center(int,int)));
        } else {
            vp = new BigMatrix(this);
            if ( technique == 3 )
                vp->enableClipper(TRUE);
            srand(1);
            for (int i=0; i<30; i++) {
                QMultiLineEdit *l = new QMultiLineEdit(vp->viewport(),"First");
                l->setText("Drag out more of these.");
                l->resize(100,100);
                vp->addChild(l, rand()%800, rand()%10000);
            }
            vp->viewport()->setBackgroundMode(NoBackground);
        }

        f_options = new QPopupMenu( menubar );
        Q_CHECK_PTR( f_options );
        f_options->setCheckable( TRUE );
        menubar->insertItem( "F&rame", f_options );
        connect( f_options, SIGNAL(activated(int)),
            this, SLOT(doFMenuItem(int)) );

        f_options->insertItem( "No Frame", style_id );
        f_options->insertItem( "Box", style_id|QFrame::Box );
        f_options->insertItem( "Panel", style_id|QFrame::Panel );
        f_options->insertItem( "WinPanel", style_id|QFrame::WinPanel );
        f_options->insertSeparator();
        f_options->insertItem( "Plain", style_id|QFrame::Plain );
        f_options->insertItem( "Raised", style_id|QFrame::Raised );
        f_laststyle = f_options->indexOf(
            f_options->insertItem( "Sunken", style_id|QFrame::Sunken ));
        f_options->insertSeparator();
        lw_options = new QPopupMenu( menubar );
        Q_CHECK_PTR( lw_options );
        lw_options->setCheckable( TRUE );
        for (int lw = 1; lw <= max_lw; lw++) {
            QString str;
            str.sprintf("%d Pixels", lw);
            lw_options->insertItem( str, lw_id | lw );
        }
        f_options->insertItem( "Line Width", lw_options );
        connect( lw_options, SIGNAL(activated(int)),
            this, SLOT(doFMenuItem(int)) );
        mlw_options = new QPopupMenu( menubar );
        Q_CHECK_PTR( mlw_options );
        mlw_options->setCheckable( TRUE );
        for (int mlw = 0; mlw <= max_mlw; mlw++) {
            QString str;
            str.sprintf("%d Pixels", mlw);
            mlw_options->insertItem( str, mlw_id | mlw );
        }
        f_options->insertItem( "Midline Width", mlw_options );
        connect( mlw_options, SIGNAL(activated(int)),
            this, SLOT(doFMenuItem(int)) );
        mw_options = new QPopupMenu( menubar );
        Q_CHECK_PTR( mw_options );
        mw_options->setCheckable( TRUE );
        for (int mw = 0; mw <= max_mw; mw++) {
            QString str;
            str.sprintf("%d Pixels", mw);
            mw_options->insertItem( str, mw_id | mw );
        }
        f_options->insertItem( "Margin Width", mw_options );
        connect( mw_options, SIGNAL(activated(int)),
            this, SLOT(doFMenuItem(int)) );

        setVPMenuItems();
        setFMenuItems();

        QVBoxLayout* vbox = new QVBoxLayout(this);
        vbox->setMenuBar(menubar);
        menubar->setSeparator(QMenuBar::InWindowsStyle);
        vbox->addWidget(vp);
        vbox->activate();

        corner = new QSizeGrip(this);
        corner->hide();
    }

private slots:
    void doVPMenuItem(int id)
    {
        if (id == vauto_id ) {
            vp->setVScrollBarMode(QScrollView::Auto);
        } else if (id == vaoff_id) {
            vp->setVScrollBarMode(QScrollView::AlwaysOff);
        } else if (id == vaon_id) {
            vp->setVScrollBarMode(QScrollView::AlwaysOn);
        } else if (id == hauto_id) {
            vp->setHScrollBarMode(QScrollView::Auto);
        } else if (id == haoff_id) {
            vp->setHScrollBarMode(QScrollView::AlwaysOff);
        } else if (id == haon_id) {
            vp->setHScrollBarMode(QScrollView::AlwaysOn);
        } else if (id == corn_id) {
            bool corn = !vp->cornerWidget();
            vp->setCornerWidget(corn ? corner : 0);
        } else {
            return; // Not for us to process.
        }
        setVPMenuItems();
    }

    void setVPMenuItems()
    {
        QScrollView::ScrollBarMode vm = vp->vScrollBarMode();
        vp_options->setItemChecked( vauto_id, vm == QScrollView::Auto );
        vp_options->setItemChecked( vaoff_id, vm == QScrollView::AlwaysOff );
        vp_options->setItemChecked( vaon_id, vm == QScrollView::AlwaysOn );

        QScrollView::ScrollBarMode hm = vp->hScrollBarMode();
        vp_options->setItemChecked( hauto_id, hm == QScrollView::Auto );
        vp_options->setItemChecked( haoff_id, hm == QScrollView::AlwaysOff );
        vp_options->setItemChecked( haon_id, hm == QScrollView::AlwaysOn );

        vp_options->setItemChecked( corn_id, !!vp->cornerWidget() );
    }

    void doFMenuItem(int id)
    {
        if (id & style_id) {
            int sty;

            if (id == style_id) {
                sty = 0;
            } else if (id & QFrame::MShape) {
                sty = vp->frameStyle()&QFrame::MShadow;
                sty = (sty ? sty : QFrame::Plain) | (id&QFrame::MShape);
            } else {
                sty = vp->frameStyle()&QFrame::MShape;
                sty = (sty ? sty : QFrame::Box) | (id&QFrame::MShadow);
            }
            vp->setFrameStyle(sty);
        } else if (id & lw_id) {
            vp->setLineWidth(id&~lw_id);
        } else if (id & mlw_id) {
            vp->setMidLineWidth(id&~mlw_id);
        } else {
            vp->setMargin(id&~mw_id);
        }

        vp->update();
        setFMenuItems();
    }

    void setFMenuItems()
    {
        int sty = vp->frameStyle();

        f_options->setItemChecked( style_id, !sty );

        for (int i=1; i <= f_laststyle; i++) {
            int id = f_options->idAt(i);
            if (id & QFrame::MShape)
                f_options->setItemChecked( id,
                    ((id&QFrame::MShape) == (sty&QFrame::MShape)) );
            else
                f_options->setItemChecked( id,
                    ((id&QFrame::MShadow) == (sty&QFrame::MShadow)) );
        }

        for (int lw=1; lw<=max_lw; lw++)
            lw_options->setItemChecked( lw_id|lw, vp->lineWidth() == lw );

        for (int mlw=0; mlw<=max_mlw; mlw++)
            mlw_options->setItemChecked( mlw_id|mlw, vp->midLineWidth() == mlw );

        for (int mw=0; mw<=max_mw; mw++)
            mw_options->setItemChecked( mw_id|mw, vp->margin() == mw );
    }

private:
    QScrollView* vp;
    QPopupMenu* vp_options;
    QPopupMenu* f_options;
    QPopupMenu* lw_options;
    QPopupMenu* mlw_options;
    QPopupMenu* mw_options;
    QSizeGrip* corner;

    int vauto_id, vaoff_id, vaon_id,
        hauto_id, haoff_id, haon_id,
        corn_id;

    int f_laststyle;
};

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

    ScrollViewExample ve1(1,0,"ve1");
    ScrollViewExample ve2(2,0,"ve2");
    ScrollViewExample ve3(3,0,"ve3");
    ve1.setCaption("Qt Example - Scrollviews");
    ve1.show();
    ve2.setCaption("Qt Example - Scrollviews");
    ve2.show();
    ve3.setCaption("Qt Example - Scrollviews");
    ve3.show();

    QObject::connect(qApp, SIGNAL(lastWindowClosed()), qApp, SLOT(quit()));

    return a.exec();
}

#include "scrollview.moc"

See also Examples.