FlowLayout doesn't take care of actual content size
Unsolved
General and Desktop
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Here my "fork" of FlowLayout, which can place the items also in vertical order:
flowlayout.h
#ifndef FLOWLAYOUT_H #define FLOWLAYOUT_H #include <QLayout> #include <QRect> #include <QStyle> class FlowLayout : public QLayout { public: explicit FlowLayout(QWidget *parent, int margin = -1, int hSpacing = -1, int vSpacing = -1); explicit FlowLayout(int margin = -1, int hSpacing = -1, int vSpacing = -1); ~FlowLayout() override; void addItem(QLayoutItem *item) override; int horizontalSpacing() const; int verticalSpacing() const; Qt::Orientations expandingDirections() const override; void setOrientation(Qt::Orientations orientation) { _orientation = orientation; } bool hasHeightForWidth() const override; int heightForWidth(int) const override; int count() const override; QLayoutItem *itemAt(int index) const override; QSize minimumSize() const override; void setGeometry(const QRect &rect) override; QSize sizeHint() const override; QLayoutItem *takeAt(int index) override; private: int doLayout(const QRect &rect, bool testOnly) const; int smartSpacing(QStyle::PixelMetric pm) const; QList<QLayoutItem *> _itemList; Qt::Orientations _orientation; int _hSpace; int _vSpace; }; #endif // FLOWLAYOUT_H
flowlayout.cpp
#include <QtWidgets> #include "flowlayout.h" FlowLayout::FlowLayout(QWidget *parent, int margin, int hSpacing, int vSpacing) : QLayout(parent), _hSpace(hSpacing), _vSpace(vSpacing) { setContentsMargins(margin, margin, margin, margin); _orientation = Qt::Horizontal; } FlowLayout::FlowLayout(int margin, int hSpacing, int vSpacing) : _hSpace(hSpacing), _vSpace(vSpacing) { setContentsMargins(margin, margin, margin, margin); _orientation = Qt::Horizontal; } FlowLayout::~FlowLayout() { QLayoutItem *item; while ((item = takeAt(0))) delete item; } void FlowLayout::addItem(QLayoutItem *item) { _itemList.append(item); } int FlowLayout::horizontalSpacing() const { if (_hSpace >= 0) return _hSpace; else return smartSpacing(QStyle::PM_LayoutHorizontalSpacing); } int FlowLayout::verticalSpacing() const { if (_vSpace >= 0) return _vSpace; else return smartSpacing(QStyle::PM_LayoutVerticalSpacing); } int FlowLayout::count() const { return _itemList.size(); } QLayoutItem *FlowLayout::itemAt(int index) const { return _itemList.value(index); } QLayoutItem *FlowLayout::takeAt(int index) { if (index >= 0 && index < _itemList.size()) return _itemList.takeAt(index); else return nullptr; } Qt::Orientations FlowLayout::expandingDirections() const { return nullptr; } bool FlowLayout::hasHeightForWidth() const { return false; } int FlowLayout::heightForWidth(int width) const { int height = doLayout(QRect(0, 0, width, 0), true); return height; } void FlowLayout::setGeometry(const QRect &rect) { QLayout::setGeometry(rect); doLayout(rect, false); } QSize FlowLayout::sizeHint() const { return minimumSize(); } QSize FlowLayout::minimumSize() const { QSize size; QLayoutItem *item; foreach (item, _itemList) size = size.expandedTo(item->minimumSize()); size += QSize(2 * margin(), 2 * margin()); return size; } int FlowLayout::doLayout(const QRect &rect, bool testOnly) const { int left, top, right, bottom; getContentsMargins(&left, &top, &right, &bottom); QRect effectiveRect = rect.adjusted(+left, +top, -right, -bottom); int x = effectiveRect.x(); int y = effectiveRect.y(); int lineHeight = 0; int colWidth = 0; QLayoutItem *item; foreach (item, _itemList) { QWidget *widget = item->widget(); int spaceX = horizontalSpacing(); if (spaceX == -1) spaceX = widget->style()->layoutSpacing(QSizePolicy::PushButton, QSizePolicy::PushButton, Qt::Horizontal); int spaceY = verticalSpacing(); if (spaceY == -1) spaceY = widget->style()->layoutSpacing(QSizePolicy::PushButton, QSizePolicy::PushButton, Qt::Vertical); switch (_orientation) { case Qt::Horizontal: { int nextX = x + item->sizeHint().width() + spaceX; if (nextX - spaceX > effectiveRect.right() && lineHeight > 0) { x = effectiveRect.x(); y = y + lineHeight + spaceY; nextX = x + item->sizeHint().width() + spaceX; lineHeight = 0; } if (!testOnly) item->setGeometry(QRect(QPoint(x, y), item->sizeHint())); x = nextX; lineHeight = qMax(lineHeight, item->sizeHint().height()); break; } case Qt::Vertical: { int nextY = y + item->sizeHint().height() + spaceY; if (nextY - spaceY > effectiveRect.bottom() && colWidth > 0) { x = x + colWidth + spaceX; y = effectiveRect.y(); nextY = y + item->sizeHint().height() + spaceY; colWidth = 0; } if (!testOnly) item->setGeometry(QRect(QPoint(x, y), item->sizeHint())); y = nextY; colWidth = qMax(colWidth, item->sizeHint().width()); break; } } } if (_orientation == Qt::Horizontal) return y + lineHeight - rect.y() + bottom; else return x + colWidth - rect.x() + right; } int FlowLayout::smartSpacing(QStyle::PixelMetric pm) const { QObject *parent = this->parent(); if (!parent) { return -1; } else if (parent->isWidgetType()) { QWidget *pw = static_cast<QWidget *>(parent); return pw->style()->pixelMetric(pm, nullptr, pw); } else { return static_cast<QLayout *>(parent)->spacing(); } }
I'm testing it mainly with vertical orientation. The problem is the horizontal scroll bar appears only when the width is less than a specific value (about 480 px) regardless the actual contents.
I think it's related to the
sizeHint()
function. I don't understand how it can calculate the needed space in both direction without doing alayout()
. Well, in fact it doesn't work!What should I change to make the horizontal scrollbar behavior reliable like the vertical one?