class ThumbnailModel : public QGalleryQueryModel
{
    Q_OBJECT
public:
    static const QSize thumbnailSize;
 
    ThumbnailModel(QAbstractGallery *gallery, QObject *parent = 0);
    ~ThumbnailModel();
 
    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const;
 
protected:
    virtual QUrl imageUrl(const QModelIndex &index) const;
 
private slots:
    void thumbnailLoaded();
 
private:
    mutable ThumbnailCache cache;
 
};
<code>
首先我们必须从 QGalleryQueryModel 派生一个类，并且重写data()方法
===ThumbnailModel.cpp===
<code>
QVariant ThumbnailModel::data(const QModelIndex &index, int role) const
{
    qDebug()<<"enter data";
    return role == Qt::DecorationRole && index.isValid()
            ? cache.thumbnail(imageUrl(index))
            : QGalleryQueryModel::data(index, role);
}

void ThumbnailModel::thumbnailLoaded()
{
    emit dataChanged(index(0, 0), index(rowCount() - 1, columnCount() -1));
}

class ThumbnailCache : public QThread
{
    Q_OBJECT
public:
    ThumbnailCache(QObject *parent = 0);
    ~ThumbnailCache();
 
    QString thumbnail(const QUrl &url);
 
    bool event(QEvent *event);
 
signals:
    void thumbnailReady();
 
protected:
    void run();
 
private:
    QImage loadImage(const QUrl &url) const;
    QString thumbnailPath(const QUrl &url) const;
 
    QMutex mutex;
    QWaitCondition waitCondition;
    QCache<QUrl, Thumbnail> cache;
    QQueue<QUrl> pendingUrls;
    bool cancelled;
};

QImage ThumbnailCache::loadImage(const QUrl &url) const
{
    const QString fileName = thumbnailPath(url);
 
    QImageReader reader(fileName);
    reader.setQuality(25);
 
    if (reader.supportsOption(QImageIOHandler::Size)) {
        QSize size = reader.size();
 
        if (!reader.supportsOption(QImageIOHandler::ScaledSize)
                && (size.width() > 1280 || size.height() > 1280)) {
            return QImage();
        }
 
        if (size.width() > ThumbnailModel::thumbnailSize.width()
                || size.height() > ThumbnailModel::thumbnailSize.height()) {
            size.scale(ThumbnailModel::thumbnailSize, Qt::KeepAspectRatio);
        }
 
        reader.setScaledSize(size);
    } else {
        reader.setScaledSize(ThumbnailModel::thumbnailSize);
    }
 
    return reader.read();
}

#ifndef PHOTODELEGATE_H
#define PHOTODELEGATE_H
 
#include <QtGui/QAbstractItemDelegate>
#include <qDebug>
class PhotoDelegate : public QAbstractItemDelegate
{
    Q_OBJECT
public:
    PhotoDelegate(QObject *parent = 0);
    ~PhotoDelegate();
 
    void paint(
            QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const;
 
    QSize sizeHint(const QStyleOptionViewItem &option, const QModelIndex &index) const;
};
 
#endif

void PhotoDelegate::paint(
        QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
    qDebug()<<"enter paint";
 
    QPen oldPen = painter->pen();
 
    QStyle *style = QApplication::style();
 
    int margin = style->pixelMetric(QStyle::PM_ButtonMargin);
 
    QRect rect = option.rect;
 
    if (option.state & QStyle::State_HasFocus) {
        painter->fillRect(rect, option.palette.highlight());
 
        painter->setPen(option.palette.color(QPalette::HighlightedText));
    }
 
    rect.adjust(margin, margin, -margin, -margin);
 
    QRect decorationRect = rect;
    decorationRect.setRight(decorationRect.left() + option.decorationSize.width());
 
    QPixmap decoration = qvariant_cast<QPixmap>(index.data(Qt::DecorationRole));
    if (!decoration.isNull())
        style->drawItemPixmap(painter, decorationRect, Qt::AlignCenter, decoration);
    else
        painter->drawRect(decorationRect);
 
    painter->setPen(oldPen);
}
 
QSize PhotoDelegate::sizeHint(const QStyleOptionViewItem &option, const QModelIndex &) const
{
    int margin = QApplication::style()->pixelMetric(QStyle::PM_ButtonMargin);
 
    QSize size = option.decorationSize;
 
    size.rheight() += 2 * margin;
    size.rwidth() += 2 * margin;
 
    return size;
}