flowlayout.cpp Example File

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 #include "flowlayout.h"
 #include <QtWidgets/qwidget.h>
 #include <QtCore/qmath.h>

 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;
 }