Basic Graphics Layouts Example 官方示例笔记

本文主要是介绍Basic Graphics Layouts Example 官方示例笔记，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

参考例子：https://doc.qt.io/qt-5/qtwidgets-graphicsview-basicgraphicslayouts-example.html

QGraphicsItem
用于绘制图形项的类。
如果想绘制自定义的图形项，需要继承该类，并实现它里面的两个虚函数：boundingRect()、paint()。
boundingRect() 用于返回 item 绘制的区域的数据，在paint() 函数里实现该 item 的具体绘制。

QGraphicsLayoutItem Class
该类是一个抽象类，通过继承该类，可以让你自定义的 item 能够被布局管理。
QGraphicsLayoutItem 定义了一组虚函数，描述了QGraphicsLayout排列的任何对象的大小、大小策略和大小提示。

QGraphicsLinearLayout Class
继承于 QGraphicsLayoutItem。
该类在Graphics View中提供水平或垂直的布局来管理Widget。默认是水平。

QGraphicsGridLayout Class
继承于 QGraphicsLayoutItem。
该类在Graphcis View中提供网格布局来管理Widget。

源码：

// window.h
#ifndef WINDOW_H
#define WINDOW_H#include <QGraphicsWidget>//! [0]
class Window : public QGraphicsWidget
{Q_OBJECT
public:Window(QGraphicsWidget *parent = nullptr);};
//! [0]#endif  //WINDOW_H

// window.cpp
#include "window.h"
#include "layoutitem.h"#include <QGraphicsLinearLayout>
#include <QGraphicsGridLayout>Window::Window(QGraphicsWidget *parent) : QGraphicsWidget(parent, Qt::Window)
{
//! [0]QGraphicsLinearLayout *windowLayout = new QGraphicsLinearLayout(Qt::Vertical);QGraphicsLinearLayout *linear = new QGraphicsLinearLayout(windowLayout);LayoutItem *item = new LayoutItem;linear->addItem(item);linear->setStretchFactor(item, 1);
//! [0]//! [1]item = new LayoutItem;linear->addItem(item);linear->setStretchFactor(item, 3);windowLayout->addItem(linear);
//! [1]//! [2]QGraphicsGridLayout *grid = new QGraphicsGridLayout(windowLayout);item = new LayoutItem;grid->addItem(item, 0, 0, 4, 1);item = new LayoutItem;item->setMaximumHeight(item->minimumHeight());grid->addItem(item, 0, 1, 2, 1, Qt::AlignVCenter);item = new LayoutItem;item->setMaximumHeight(item->minimumHeight());grid->addItem(item, 2, 1, 2, 1, Qt::AlignVCenter);item = new LayoutItem;grid->addItem(item, 0, 2);item = new LayoutItem;grid->addItem(item, 1, 2);item = new LayoutItem;grid->addItem(item, 2, 2);item = new LayoutItem;grid->addItem(item, 3, 2);windowLayout->addItem(grid);
//! [2]//! [3]setLayout(windowLayout);setWindowTitle(tr("Basic Graphics Layouts Example"));
//! [3]
}

// layoutitem.h
#ifndef LAYOUTITEM_H
#define LAYOUTITEM_H#include <QGraphicsLayoutItem>
#include <QGraphicsItem>
#include <QPixmap>//! [0]
class LayoutItem : public QGraphicsLayoutItem, public QGraphicsItem
{
public:LayoutItem(QGraphicsItem *parent = nullptr);// Inherited from QGraphicsLayoutItemvoid setGeometry(const QRectF &geom) override;QSizeF sizeHint(Qt::SizeHint which, const QSizeF &constraint = QSizeF()) const override;// Inherited from QGraphicsItemQRectF boundingRect() const override;void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = nullptr) override;private:QPixmap m_pix;
};
//! [0]#endif // LAYOUTITEM_H

// layoutitem.cpp
#include "layoutitem.h"#include <QGradient>
#include <QPainter>//! [0]
LayoutItem::LayoutItem(QGraphicsItem *parent): QGraphicsLayoutItem(), QGraphicsItem(parent),m_pix(QPixmap(QLatin1String("../layoutdemo1-copy/block.png")))
{setGraphicsItem(this);
}
//! [0]//! [1]
void LayoutItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option,QWidget *widget)
{Q_UNUSED(widget);Q_UNUSED(option);QRectF frame(QPointF(0, 0), geometry().size());const QSizeF pmSize = m_pix.size();QGradientStops stops;
//! [1]//! [2]// paint a background rect (with gradient)QLinearGradient gradient(frame.topLeft(), frame.topLeft() + QPointF(200,200));stops << QGradientStop(0.0, QColor(60, 60,  60));stops << QGradientStop(frame.height() / 2 / frame.height(), QColor(102, 176, 54));//stops << QGradientStop(((frame.height() + h)/2 )/frame.height(), QColor(157, 195,  55));stops << QGradientStop(1.0, QColor(215, 215, 215));gradient.setStops(stops);painter->setBrush(QBrush(gradient));painter->drawRoundedRect(frame, 10.0, 10.0);// paint a rect around the pixmap (with gradient)QPointF pixpos = frame.center() - (QPointF(pmSize.width(), pmSize.height()) / 2);QRectF innerFrame(pixpos, pmSize);innerFrame.adjust(-4, -4, 4, 4);gradient.setStart(innerFrame.topLeft());gradient.setFinalStop(innerFrame.bottomRight());stops.clear();stops << QGradientStop(0.0, QColor(215, 255, 200));stops << QGradientStop(0.5, QColor(102, 176, 54));stops << QGradientStop(1.0, QColor(0, 0,  0));gradient.setStops(stops);painter->setBrush(QBrush(gradient));painter->drawRoundedRect(innerFrame, 10.0, 10.0);painter->drawPixmap(pixpos, m_pix);
}
//! [2]//! [3]
QRectF LayoutItem::boundingRect() const
{return QRectF(QPointF(0, 0), geometry().size());
}
//! [3]//! [4]
void LayoutItem::setGeometry(const QRectF &geom)
{prepareGeometryChange();QGraphicsLayoutItem::setGeometry(geom);setPos(geom.topLeft());
}
//! [4]//! [5]
QSizeF LayoutItem::sizeHint(Qt::SizeHint which, const QSizeF &constraint) const
{switch (which) {case Qt::MinimumSize:case Qt::PreferredSize:// Do not allow a size smaller than the pixmap with two frames around it.return m_pix.size() + QSize(12, 12);case Qt::MaximumSize:return QSizeF(1000,1000);default:break;}return constraint;
}
//! [5]