flowlayout.cpp Example File

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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;
  }