Qt使用flowlayout，使控件两端间距始终固定，垂直和水平间距相等

先上代码：

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(QWidget *parent, bool home,int margin = -1, int hSpacing = -1, int vSpacing = -1 );explicit FlowLayout(int margin = -1, int hSpacing = -1, int vSpacing = -1);~FlowLayout();public: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;int fillSpaceX(QWidget *wid) const;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;bool m_home = false;};

flowlayout.cpp:

#include "flowlayout.h"#include <QWidget>
#include <QDebug>
#include <QtMath>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(QWidget *parent, bool home, int margin, int hSpacing, int vSpacing):QLayout(parent),m_hSpace(hSpacing),m_vSpace(vSpacing),m_home(home)
{setContentsMargins(margin, margin, margin, margin);
}FlowLayout::FlowLayout(int margin, int hSpacing, int vSpacing): m_hSpace(hSpacing),m_vSpace(vSpacing)
{setContentsMargins(margin, margin, margin, margin);
}FlowLayout::~FlowLayout(){QLayoutItem * item;while ((item = takeAt(0))) {}
}void FlowLayout::addItem(QLayoutItem *item){itemList.append(item);
}int FlowLayout::horizontalSpacing() const{if (m_hSpace >= 0 || m_hSpace == -1) {return m_hSpace;} else {return smartSpacing(QStyle::PM_LayoutHorizontalSpacing);}
}int FlowLayout::verticalSpacing() const{if (m_vSpace >= 0 || m_vSpace == -1) {return m_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);elsereturn 0;
}Qt::Orientations FlowLayout::expandingDirections() const{return 0;
}bool FlowLayout::hasHeightForWidth() const{return true;
}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 fillX = 0;bool bFillX = false;QLayoutItem *item;foreach (item, itemList) {QWidget *wid = item->widget();int spaceX = horizontalSpacing();if (spaceX == -1) {if (!bFillX) {bFillX = true;fillX = fillSpaceX(wid);}spaceX = fillX;}int spaceY = verticalSpacing();if (spaceY == -1 && fillX >= 0) {spaceY = fillX;} else {spaceY = wid->style()->layoutSpacing(QSizePolicy::PushButton, QSizePolicy::PushButton, Qt::Vertical);}if (m_home) {spaceY = 32;}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 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, 0, pw);} else {return static_cast<QLayout *>(parent)->spacing();}
}int FlowLayout::fillSpaceX(QWidget *wid) const{int num = 0;int x = 0;int numH = 0;int space  = 4;if (m_home) {space = 24;}int len = this->parentWidget()->width() - this->contentsMargins().left() - this->contentsMargins().right();while (true) {num++;if (num * (wid->width() + space) - space >= len) {  //最小间距spacebreak;}}num = num - 1;if (num <= 1) {numH = itemList.size();return 32;}int height = wid->height();numH = ceil(double(itemList.size()) / num);x = len + space - num * (wid->width() + space);x = ceil(double(x)/(num - 1)) +space;x = x - 1;   //考虑边框等因素影响int maxY = numH * (height + x) + 32 - x;if (m_home) {maxY = numH * (height + 24) + 32;}this->parentWidget()->setFixedHeight(maxY);return x;
}

使用效果一:

FlowLayout * flowLayout = new FlowLayout(ui->widget_2, true, 0);
flowLayout->setContentsMargins(70, 0, 70, 0);
/*.....*/
flowLayout->addWidget(baseWidget);

使用效果二：

picFlowLayout = new FlowLayout(ui->picFrame,16, -1, -1);
ui->picFrame->setLayout(picFlowLayout);
/*.....................*/
picFlowLayout->addWidget(picUnit);

注意，不能直接在滚动控件的widget里面去设置这个flowLayout，否则可能会导致在改变大小的时候出现段错误(一直循环在修改size)。例如在效果一中，如果直接设置父对象为scrollAreaWidgetContents_5，当在首页改变控制面板窗口大小时，就会出现闪退的情况，所以这里添加了一个widget。使用QT提供的flowlayout不会有此问题，猜测是因为新加的fillSpaceX()函数中会修改父窗口的高度导致。

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