QT笔记——自定义的流式布局QFlowLayout

想要实现一个流式布局，如下：

就在网上搜索了 关于流式布局的相关例子
代码如下：
QFlowLayout.h

#pragma once

#include <QLayout>
#include <QStyle>

class QFlowLayout : public QLayout
{
    
	Q_OBJECT

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;		//layout的子项
	int m_hSpace;						
	int m_vSpace;
};

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);  // 边缘间距
}

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

QFlowLayout::~QFlowLayout()
{
    
	QLayoutItem* item;
	// 内部所有内容析构
	while ((item = takeAt(0)))
		delete item;
}

void QFlowLayout::addItem(QLayoutItem* item)
{
    
	itemList.append(item);  // 将项目添加到布局
}

int QFlowLayout::horizontalSpacing() const
{
    
	// 小部件之间的间距
	if (m_hSpace >= 0) {
    
		return m_hSpace;
	}
	else {
    
		return smartSpacing(QStyle::PM_LayoutHorizontalSpacing);  // 在没有间隔的时候自动智能生成一段间隔
	}
}

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

int QFlowLayout::count() const
{
    
	return itemList.size(); // 返回布局中的项目数
}

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);  // 删除并返回项目, 如果某个项目被删除，其余的项目将被重新编号。
	return nullptr;
}

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);  // 高度取决于宽度的窗口小部件
	return height;
}

void QFlowLayout::setGeometry(const QRect& rect)
{
    
	// 计算布局项目的几何形状
	QLayout::setGeometry(rect);
	doLayout(rect, false);
}

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

QSize QFlowLayout::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;
}

int QFlowLayout::doLayout(const QRect& rect, bool testOnly) const
{
    
	int left, top, right, bottom;
	getContentsMargins(&left, &top, &right, &bottom);  // 计算布局项目可用的面积
	QRect effectiveRect = rect.adjusted(+left, +top, -right, -bottom);
	int x = effectiveRect.x();
	int y = effectiveRect.y();
	int lineHeight = 0;

	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);


		int nextX = x + item->sizeHint().width() + spaceX;  // 下一个item的x坐标
		if (nextX - spaceX > effectiveRect.right() && lineHeight > 0) {
      // 当前item的x坐标超过边界
			// 设置为下一行的第一个
			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
{
    
	// 当父是QWidget=>顶层布局的默认间距为pm样式。
	// 当父为QLayout=>子布局的默认间距由父布局的间距来确定。
	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();
	}
}

QFlowLayoutTest.cpp

#include "QFlowLayoutTest.h"

QFlowLayoutTest::QFlowLayoutTest(QWidget* parent)
	: QWidget(parent)
{
    
	ui.setupUi(this);

	flowLayout = new QFlowLayout(this,20,20,20);
	for (int i = 0; i < 10; i++) 
	{
    
		QPushButton* p = new QPushButton(QString::number(i));
		p->setFixedSize(80, 40);
		this->flowLayout->addWidget(p);
	}
}

参考博客：
调整的流式布局的BUG
流式布局