Qt使用QGraphicsView实现滑动窗体效果

   QGraphicsView用来显示一个滚动视图区的QGraphicsScene内容。QGraphicsScene提供了QGraphicsItem的容器功能。通常与QGraphicsView一起使用来描述可视化图形项目。

   QGraphicsScene提供了一个视图的场景，通过在这样一个场景之上加入不同的QGraphicsItem来构建视图。而QGraphicsView则提供了一个widget来显示QGraphicsScene的内容。所以要想成功构建一个视图，这三个元素缺一不可。

   以下是一个QGraphicsView的例子，实现滑动的窗体效果，工具栏和图片均为场景中的Item。

#include <QtCore>  
#include <QtGui>  
#include <QtSvg>  
/*程序中用到了svg格式的图片，所以需包含QtSvg*/  
#define PAGE_COUNT 5  
/*定义滑动窗体的窗体数*/ 

       定义工具栏，NviBar继承自QGraphicsRectItem，用法与QGraphicsItem类似。

class NaviBar : public QObject, public QGraphicsRectItem  
{  
    Q_OBJECT  
public:  
    NaviBar();  
    void setPageOffset(qreal ofs);  
signals:  
    void pageSelected(int page);  
protected:  
    void mousePressEvent(QGraphicsSceneMouseEvent *event);  
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = 0);  
private:  
    QList<QGraphicsSvgItem*> m_icons;  
    QGraphicsRectItem *m_cursor;  
};  

函数实现

#define ICON_SIZE 50  
#define ICON_PAD 4  
NaviBar::NaviBar()  
        : QGraphicsRectItem()  
{  
    setRect(0, 0, 5 * ICON_SIZE, ICON_SIZE);  
    setPen(Qt::NoPen);  
    QStringList names;  
    names << "map" << "web" << "home" << "weather" << "contacts";  
    for (int i = 0; i < names.count(); ++i) {  
        QString fname = names[i];  
        fname.prepend(":/icons/");  
        fname.append("-page.svg");  
        QGraphicsSvgItem *icon = new QGraphicsSvgItem(fname);  
        icon->setParentItem(this);  
        const int dim = ICON_SIZE - ICON_PAD * 2;  
        qreal sw = dim / icon->boundingRect().width();  
        qreal sh = dim / icon->boundingRect().height();  
        icon->setTransform(QTransform().scale(sw, sh));  
        icon->setZValue(2);  
        m_icons << icon;  
    }  
    m_cursor = new QGraphicsRectItem;  
    m_cursor->setParentItem(this);  
    m_cursor->setRect(0, 0, ICON_SIZE, ICON_SIZE);  
    m_cursor->setZValue(1);  
    m_cursor->setPen(Qt::NoPen);  
    m_cursor->setBrush(QColor(Qt::white));  
    m_cursor->setOpacity(0.6);  
}  
void NaviBar::setPageOffset(qreal ofs)  
{  
    m_cursor->setPos(ofs * ICON_SIZE, 0);  
    for (int i = 0; i < m_icons.count(); ++i) {  
        int y = (i == static_cast<int>(ofs + 0.5)) ? ICON_PAD : ICON_PAD * 2;  
        m_icons[i]->setPos(i * ICON_SIZE + ICON_PAD, y);  
        m_icons[i]->setOpacity(1);  
    }  
}  
void NaviBar::mousePressEvent(QGraphicsSceneMouseEvent *event)  
{  
    emit pageSelected(static_cast<int>(event->pos().x() / ICON_SIZE));  
}  
void NaviBar::paint(QPainter * painter, const QStyleOptionGraphicsItem *option, QWidget *widget)  
{  
    painter->setBrush(Qt::white);  
    painter->setOpacity(0.2);  
    painter->drawRect(option->rect.adjusted(-20, ICON_PAD, 20, 0));  
}  
 

定义视图

class ParallaxHome: public QGraphicsView  
{  
    Q_OBJECT  
public:  
    QGraphicsScene m_scene;  
    NaviBar *m_naviBar;  
    QGraphicsPixmapItem *m_wallpaper;  
    QTimeLine m_pageAnimator;  
    qreal m_pageOffset;  
    QList<QGraphicsPixmapItem*> m_items;  
    QList<QPointF> m_positions;  
public:  
    ParallaxHome(QWidget *parent = 0)  
            : QGraphicsView(parent)  
            , m_pageOffset(-2) {  
        setupScene();  
        setScene(&m_scene);  
        setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);  
        setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);  
        setFrameShape(QFrame::NoFrame);  
        setWindowTitle("Parallax Home");  
        connect(&m_pageAnimator, SIGNAL(frameChanged(int)), SLOT(shiftPage(int)));  
        m_pageAnimator.setDuration(500);  
        m_pageAnimator.setFrameRange(0, 100);  
        m_pageAnimator.setCurveShape(QTimeLine::EaseInCurve);  
        pageChanged(static_cast<int>(m_pageOffset));  
    }  
signals:  
    void pageChanged(int page);  
public slots:  
    void slideRight() {  
        if (m_pageAnimator.state() != QTimeLine::NotRunning)  
            return;  
        int edge = -(m_pageOffset - 1);  
        if (edge < PAGE_COUNT)  
            slideBy(-1);  
    }  
    void slideLeft() {  
        if (m_pageAnimator.state() != QTimeLine::NotRunning)  
            return;  
        if (m_pageOffset < 0)  
            slideBy(1);  
    }  
    void slideBy(int dx) {  
        int start = m_pageOffset * 1000;  
        int end = (m_pageOffset + dx) * 1000;  
        m_pageAnimator.setFrameRange(start, end);  
        m_pageAnimator.start();  
    }  
    void choosePage(int page) {  
        if (m_pageAnimator.state() != QTimeLine::NotRunning)  
            return;  
        if (static_cast<int>(-m_pageOffset) == page)  
            return;  
        slideBy(-page - m_pageOffset);  
    }  
private slots:  
    void shiftPage(int frame) {  
        int ww = width();  
        int hh = height() - m_naviBar->rect().height();  
        int oldPage = static_cast<int>(-m_pageOffset);  
        m_pageOffset = static_cast<qreal>(frame) / qreal(1000);  
        int newPage = static_cast<int>(-m_pageOffset);  
        m_naviBar->setPageOffset(-m_pageOffset);  
        if (oldPage != newPage)  
            emit pageChanged(newPage);  
        int ofs = m_pageOffset * ww;  
        for (int i = 0; i < m_items.count(); ++i) {  
            QPointF pos = m_positions[i];  
            QPointF xy(pos.x() * ww, pos.y() * hh);  
            m_items[i]->setPos(xy + QPointF(ofs, 0));  
        }  
        int center = m_wallpaper->pixmap().width() / 2;  
        const int parallax = 3;  
        int base = center - (ww / 2) - (PAGE_COUNT >> 1) * (ww / parallax);  
        int wofs = base - m_pageOffset * ww / parallax;  
        m_wallpaper->setPos(-wofs, 0);  
    }  
protected:  
    void resizeEvent(QResizeEvent *event) {  
        Q_UNUSED(event);  
        layoutScene();  
    }  
    void keyPressEvent(QKeyEvent *event) {  
        if (event->key() == Qt::Key_Right)  
            slideRight();  
        if (event->key() == Qt::Key_Left)  
            slideLeft();  
        event->accept();  
    }  
private:  
    void layoutScene() {  
        int ww = width();  
        int hh = height();  
        m_scene.setSceneRect(0, 0, PAGE_COUNT * ww - 1, hh - 1);  
        centerOn(ww / 2, hh / 2);  
        int nw = m_naviBar->rect().width();  
        int nh = m_naviBar->rect().height();  
        m_naviBar->setPos((ww - nw) / 2, hh - nh);  
        shiftPage(m_pageOffset * 1000);  
    }  
    void setupScene() {  
        qsrand(QTime::currentTime().second());  
        QStringList names;  
        names << "brownies" << "cookies" << "mussels" << "pizza" << "sushi";  
        names << "chocolate" << "fish" << "pasta" << "puding" << "trouts";  
        for (int i = 0; i < PAGE_COUNT * 2; ++i) {  
            QString fname = names[i];  
            fname.prepend(":/images/");  
            fname.append(".jpg");  
            QPixmap pixmap(fname);  
            pixmap = pixmap.scaledToWidth(200);  
            QGraphicsPixmapItem *item = m_scene.addPixmap(pixmap);  
            m_items << item;  
            qreal x = (i >> 1) + (qrand() % 30) / 100.0;  
            qreal y = (i & 1) / 2.0  + (qrand() % 20) / 100.0;  
            m_positions << QPointF(x, y);  
            item->setZValue(1);  
        }  
        m_naviBar = new NaviBar;  
        m_scene.addItem(m_naviBar);  
        m_naviBar->setZValue(2);  
        connect(m_naviBar, SIGNAL(pageSelected(int)), SLOT(choosePage(int)));  
        m_wallpaper = m_scene.addPixmap(QPixmap(":/icons/surfacing.png"));  
        m_wallpaper->setZValue(0);  
        m_scene.setItemIndexMethod(QGraphicsScene::NoIndex);  
    }  
};  
 

main函数

#include "parallaxhome.moc"  
int main(int argc, char *argv[])  
{  
    QApplication app(argc, argv);  
    ParallaxHome w;  
    w.resize(360, 640);  
    w.show();  
    return app.exec();  
}