Add FlowLayout class for responsive UI

src/FlowLayout.cpp

@@ -0,0 +1,171 @@
+#include <QtWidgets>
+#include "FlowLayout.h"
+
+//! [1]
+FlowLayout::FlowLayout(QWidget *parent, int margin, int hSpacing, int vSpacing)
+    : QLayout(parent), m_hSpace(hSpacing), m_vSpace(vSpacing)
+{
+    setContentsMargins(margin, margin, margin, margin);
+}
+
+FlowLayout::FlowLayout(int margin, int hSpacing, int vSpacing)
+    : m_hSpace(hSpacing), m_vSpace(vSpacing)
+{
+    setContentsMargins(margin, margin, margin, margin);
+}
+//! [1]
+
+//! [2]
+FlowLayout::~FlowLayout()
+{
+    QLayoutItem *item;
+    while ((item = takeAt(0)))
+        delete item;
+}
+//! [2]
+
+//! [3]
+void FlowLayout::addItem(QLayoutItem *item)
+{
+    itemList.append(item);
+}
+//! [3]
+
+//! [4]
+int FlowLayout::horizontalSpacing() const
+{
+    if (m_hSpace >= 0) {
+        return m_hSpace;
+    } else {
+        return smartSpacing(QStyle::PM_LayoutHorizontalSpacing);
+    }
+}
+
+int FlowLayout::verticalSpacing() const
+{
+    if (m_vSpace >= 0) {
+        return m_vSpace;
+    } else {
+        return smartSpacing(QStyle::PM_LayoutVerticalSpacing);
+    }
+}
+//! [4]
+
+//! [5]
+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);
+    return nullptr;
+}
+//! [5]
+
+//! [6]
+Qt::Orientations FlowLayout::expandingDirections() const
+{
+    return { };
+}
+//! [6]
+
+//! [7]
+bool FlowLayout::hasHeightForWidth() const
+{
+    return true;
+}
+
+int FlowLayout::heightForWidth(int width) const
+{
+    int height = doLayout(QRect(0, 0, width, 0), true);
+    return height;
+}
+//! [7]
+
+//! [8]
+void FlowLayout::setGeometry(const QRect &rect)
+{
+    QLayout::setGeometry(rect);
+    doLayout(rect, false);
+}
+
+QSize FlowLayout::sizeHint() const
+{
+    return minimumSize();
+}
+
+QSize FlowLayout::minimumSize() const
+{
+    QSize size;
+    for (const QLayoutItem *item : std::as_const(itemList))
+        size = size.expandedTo(item->minimumSize());
+
+    const QMargins margins = contentsMargins();
+    size += QSize(margins.left() + margins.right(), margins.top() + margins.bottom());
+    return size;
+}
+//! [8]
+
+//! [9]
+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;
+//! [9]
+
+//! [10]
+    for (QLayoutItem *item : std::as_const(itemList)) {
+        const QWidget *wid = item->widget();
+        int spaceX = horizontalSpacing();
+        if (spaceX == -1)
+            spaceX = wid->style()->layoutSpacing(
+                QSizePolicy::PushButton, QSizePolicy::PushButton, Qt::Horizontal);
+        int spaceY = verticalSpacing();
+        if (spaceY == -1)
+            spaceY = wid->style()->layoutSpacing(
+                QSizePolicy::PushButton, QSizePolicy::PushButton, Qt::Vertical);
+//! [10]
+//! [11]
+        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());
+    }
+    return y + lineHeight - rect.y() + bottom;
+}
+//! [11]
+//! [12]
+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();
+    }
+}
+//! [12]

src/FlowLayout.h

@@ -0,0 +1,39 @@
+#ifndef FLOWLAYOUT_H
+#define FLOWLAYOUT_H
+
+#include <QLayout>
+#include <QRect>
+#include <QStyle>
+
+//! [0]
+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();
+
+    void addItem(QLayoutItem *item) override;
+    int horizontalSpacing() const;
+    int verticalSpacing() const;
+    Qt::Orientations expandingDirections() const override;
+    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;
+    int m_hSpace;
+    int m_vSpace;
+};
+//! [0]
+
+#endif // FLOWLAYOUT_H