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前言

最近在做一个需求需要流式布局，虽然官方example里有一个流式布局范例，但是不能满足我的需求，我需要支持插入的流式布局，所以就改造了下。

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一、源代码

由于我是基于官方改造的，所以就不去大张旗鼓解释了，总体就是增加一个方法：void insertWidget(int index, QWidget *widget);这里给出源代码大家可以自行研究。

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;void insertWidget(int index, QWidget *widget);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;
};

FlowLayout .cpp

/****************************************************************************
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****************************************************************************/#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);
}void FlowLayout::insertWidget(int index, QWidget *widget)
{if (index < 0 || index > itemList.size()) {index = itemList.size();}QLayoutItem *item = new QWidgetItem(widget);itemList.insert(index, item);addChildWidget(widget);update();
}
//! [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 : qAsConst(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 : qAsConst(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]

测试代码：

    FlowLayout *flowLayout = new FlowLayout;flowLayout->addWidget(new QPushButton(tr("Short")));flowLayout->addWidget(new QPushButton(tr("Longer")));flowLayout->addWidget(new QPushButton(tr("Different text")));flowLayout->addWidget(new QPushButton(tr("More text")));flowLayout->addWidget(new QPushButton(tr("Even longer button text")));flowLayout->insertWidget(flowLayout->count()-1,new QPushButton(tr("Insert")));

二、删除代码

顺便提一嘴，正常可能没有删除需求，但是如果你想删除控件的话单靠QLayout自带的removeWidget就不行了。下面就介绍删除方法，
假设你插入的QWidget叫w，这里要将w彻底回收掉才行，单纯从布局中删除是不够的，所以你插入或加入的控件指针要提前保留下来，等到从流式布局删除的时候需要用到它。

flowLayout->removeWidget(w);
w->deleteLater();

三、扩展

我最近做了一个类似于Ant的Select效果的控件,主要基于流式布局。

思路就是流式布局里插入一个输入框，当输入框获取焦点的时候弹出下拉框，下拉框可以多选。然后输入框可以搜索过滤。

可以通过点击控件外部让下拉框消失。

可以通过重复点击下拉框选项或选项流式布局里面的X按钮清除选项解决内容被篡改的问题。

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总结

1、总体难度还行
2、代码从官方示例中改进而来，基本能满足我的需求。