- Qt 5.5
- Qt Widgets
- Graphics View Flow Layout Example
- flowlayout.cpp Example File
- Qt 5.5.1 Reference Documentation

# flowlayout.cpp Example File

graphicsview/flowlayout/flowlayout.cpp

    /****************************************************************************
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    ** This file is part of the examples of the Qt Toolkit.
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    #include "flowlayout.h"

    #include <qmath.h>

    #include <QWidget>

    FlowLayout::FlowLayout()
    {
        m_spacing[0] = 6;
        m_spacing[1] = 6;
        QSizePolicy sp = sizePolicy();
        sp.setHeightForWidth(true);
        setSizePolicy(sp);
    }

    void FlowLayout::insertItem(int index, QGraphicsLayoutItem *item)
    {
        item->setParentLayoutItem(this);
        if (uint(index) > uint(m_items.count()))
            index = m_items.count();
        m_items.insert(index, item);
        invalidate();
    }

    int FlowLayout::count() const
    {
        return m_items.count();
    }

    QGraphicsLayoutItem *FlowLayout::itemAt(int index) const
    {
        return m_items.value(index);
    }

    void FlowLayout::removeAt(int index)
    {
        m_items.removeAt(index);
        invalidate();
    }

    qreal FlowLayout::spacing(Qt::Orientation o) const
    {
        return m_spacing[int(o) - 1];
    }

    void FlowLayout::setSpacing(Qt::Orientations o, qreal spacing)
    {
        if (o & Qt::Horizontal)
            m_spacing[0] = spacing;
        if (o & Qt::Vertical)
            m_spacing[1] = spacing;
    }

    void FlowLayout::setGeometry(const QRectF &geom)
    {
        QGraphicsLayout::setGeometry(geom);
        doLayout(geom, true);
    }

    qreal FlowLayout::doLayout(const QRectF &geom, bool applyNewGeometry) const
    {
        qreal left, top, right, bottom;
        getContentsMargins(&left, &top, &right, &bottom);
        const qreal maxw = geom.width() - left - right;

        qreal x = 0;
        qreal y = 0;
        qreal maxRowHeight = 0;
        QSizeF pref;
        for (int i = 0; i < m_items.count(); ++i) {
            QGraphicsLayoutItem *item = m_items.at(i);
            pref = item->effectiveSizeHint(Qt::PreferredSize);
            maxRowHeight = qMax(maxRowHeight, pref.height());

            qreal next_x;
            next_x = x + pref.width();
            if (next_x > maxw) {
                if (x == 0) {
                    pref.setWidth(maxw);
                } else {
                    x = 0;
                    next_x = pref.width();
                }
                y += maxRowHeight + spacing(Qt::Vertical);
                maxRowHeight = 0;
            }

            if (applyNewGeometry)
                item->setGeometry(QRectF(QPointF(left + x, top + y), pref));
            x = next_x + spacing(Qt::Horizontal);
        }
        maxRowHeight = qMax(maxRowHeight, pref.height());
        return top + y + maxRowHeight + bottom;
    }

    QSizeF FlowLayout::minSize(const QSizeF &constraint) const
    {
        QSizeF size(0, 0);
        qreal left, top, right, bottom;
        getContentsMargins(&left, &top, &right, &bottom);
        if (constraint.width() >= 0) {   // height for width
            const qreal height = doLayout(QRectF(QPointF(0,0), constraint), false);
            size = QSizeF(constraint.width(), height);
        } else if (constraint.height() >= 0) {  // width for height?
            // not supported
        } else {
            QGraphicsLayoutItem *item;
            foreach (item, m_items)
                size = size.expandedTo(item->effectiveSizeHint(Qt::MinimumSize));
            size += QSize(left + right, top + bottom);
        }
        return size;
    }

    QSizeF FlowLayout::prefSize() const
    {
        qreal left, right;
        getContentsMargins(&left, 0, &right, 0);

        QGraphicsLayoutItem *item;
        qreal maxh = 0;
        qreal totalWidth = 0;
        foreach (item, m_items) {
            if (totalWidth > 0)
                totalWidth += spacing(Qt::Horizontal);
            QSizeF pref = item->effectiveSizeHint(Qt::PreferredSize);
            totalWidth += pref.width();
            maxh = qMax(maxh, pref.height());
        }
        maxh += spacing(Qt::Vertical);

        const qreal goldenAspectRatio = 1.61803399;
        qreal w = qSqrt(totalWidth * maxh * goldenAspectRatio) + left + right;

        return minSize(QSizeF(w, -1));
    }

    QSizeF FlowLayout::maxSize() const
    {
        QGraphicsLayoutItem *item;
        qreal totalWidth = 0;
        qreal totalHeight = 0;
        foreach (item, m_items) {
            if (totalWidth > 0)
                totalWidth += spacing(Qt::Horizontal);
            if (totalHeight > 0)
                totalHeight += spacing(Qt::Vertical);
            QSizeF pref = item->effectiveSizeHint(Qt::PreferredSize);
            totalWidth += pref.width();
            totalHeight += pref.height();
        }

        qreal left, top, right, bottom;
        getContentsMargins(&left, &top, &right, &bottom);
        return QSizeF(left + totalWidth + right, top + totalHeight + bottom);
    }

    QSizeF FlowLayout::sizeHint(Qt::SizeHint which, const QSizeF &constraint) const
    {
        QSizeF sh = constraint;
        switch (which) {
        case Qt::PreferredSize:
            sh = prefSize();
            break;
        case Qt::MinimumSize:
            sh = minSize(constraint);
            break;
        case Qt::MaximumSize:
            sh = maxSize();
            break;
        default:
            break;
        }
        return sh;
    }