Qt之自定义布局管理器（QFlowLayout）

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。

简述

实现

效果

源码

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();
}
}