简述

QFlowLayout，顾名思义-流布局，实现了处理不同窗口大小的布局。根据应用窗口的宽度来进行控件放置的变化。

具体实现要求不再赘述，请参考前两节内容。

实现

QFlowLayout主要采用QLayout和QWidgetItem实现，而窗口使用了QWidget和QPushButton。

效果

源码

QFlowLayout.h

#ifndef QFLOWLAYOUT_H
#define QFLOWLAYOUT_H

#include <QLayout>
#include <QRect>
#include <QStyle>

class QFlowLayout : public QLayout
{
public:
    explicit QFlowLayout(QWidget *parent, int margin = -1, int hSpacing = -1, int vSpacing = -1);
    explicit QFlowLayout(int margin = -1, int hSpacing = -1, int vSpacing = -1);
    ~QFlowLayout();

    void addItem(QLayoutItem *item) Q_DECL_OVERRIDE;
    int horizontalSpacing() const;
    int verticalSpacing() const;
    Qt::Orientations expandingDirections() const Q_DECL_OVERRIDE;
    bool hasHeightForWidth() const Q_DECL_OVERRIDE;
    int heightForWidth(int) const Q_DECL_OVERRIDE;
    int count() const Q_DECL_OVERRIDE;
    QLayoutItem *itemAt(int index) const Q_DECL_OVERRIDE;
    QSize minimumSize() const Q_DECL_OVERRIDE;
    void setGeometry(const QRect &rect) Q_DECL_OVERRIDE;
    QSize sizeHint() const Q_DECL_OVERRIDE;
    QLayoutItem *takeAt(int index) Q_DECL_OVERRIDE;

private:
    int doLayout(const QRect &rect, bool testOnly) const;
    int smartSpacing(QStyle::PixelMetric pm) const;

private:
    QList<QLayoutItem *> itemList;
    int m_hSpace;
    int m_vSpace;
};

#endif // QFLOWLAYOUT_H

QFlowLayout.cpp

#include <QWidget>
#include "QFlowLayout.h"

QFlowLayout::QFlowLayout(QWidget *parent, int margin, int hSpacing, int vSpacing)
    : QLayout(parent),
      m_hSpace(hSpacing),
      m_vSpace(vSpacing)
{
    setContentsMargins(margin, margin, margin, margin);
}

QFlowLayout::QFlowLayout(int margin, int hSpacing, int vSpacing)
    : m_hSpace(hSpacing),
      m_vSpace(vSpacing)
{
    setContentsMargins(margin, margin, margin, margin);
}

QFlowLayout::~QFlowLayout()
{
    QLayoutItem *item;
    while ((item = takeAt(0)))
        delete item;
}

void QFlowLayout::addItem(QLayoutItem *item)
{
    itemList.append(item);
}

int QFlowLayout::horizontalSpacing() const
{
    if (m_hSpace >= 0) {
        return m_hSpace;
    } else {
        return smartSpacing(QStyle::PM_LayoutHorizontalSpacing);
    }
}

int QFlowLayout::verticalSpacing() const
{
    if (m_vSpace >= 0) {
        return m_vSpace;
    } else {
        return smartSpacing(QStyle::PM_LayoutVerticalSpacing);
    }
}

int QFlowLayout::count() const
{
    return itemList.size();
}

QLayoutItem *QFlowLayout::itemAt(int index) const
{
    return itemList.value(index);
}

QLayoutItem *QFlowLayout::takeAt(int index)
{
    if (index >= 0 && index < itemList.size())
        return itemList.takeAt(index);
    else
        return 0;
}

Qt::Orientations QFlowLayout::expandingDirections() const
{
    return 0;
}

bool QFlowLayout::hasHeightForWidth() const
{
    return true;
}

int QFlowLayout::heightForWidth(int width) const
{
    int height = doLayout(QRect(0, 0, width, 0), true);
    return height;
}

void QFlowLayout::setGeometry(const QRect &rect)
{
    QLayout::setGeometry(rect);
    doLayout(rect, false);
}

QSize QFlowLayout::sizeHint() const
{
    return minimumSize();
}

QSize QFlowLayout::minimumSize() const
{
    QSize size;
    QLayoutItem *item;
    foreach (item, itemList)
        size = size.expandedTo(item->minimumSize());

    size += QSize(2*margin(), 2*margin());
    return size;
}

int QFlowLayout::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;

    QLayoutItem *item;
    foreach (item, itemList) {
        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);

        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;
}

int QFlowLayout::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, 0, pw);
    } else {
        return static_cast<QLayout *>(parent)->spacing();
    }
}