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说明

在使用Qt的图形视图框架实现功能时，一般会在其基础上进行自定义功能实现。
如：滚轮对场景的缩放，鼠标拖动场景中的项，以及可以在场景中进行右键操作等。

示例

myitem为自定义QGraphicsItem，实现了边框、重绘事件、鼠标悬停、按键、右键菜单等功能。

myitem.h

#ifndef MYITEM_H
#define MYITEM_H#include <QGraphicsItem>class MyItem : public QGraphicsItem
{
public:MyItem();// 边框virtual QRectF boundingRect() const override;// 重绘事件virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option,QWidget *widget) override;// 设置笔刷inline void setColor(const QColor &color) {brushColor = color;}protected:// 鼠标按下函数，设置被点击的图形项得到焦点，并改变光标外观virtual void keyPressEvent(QKeyEvent *event) override;// 键盘按下函数，判断是不是向下方向键，若是是，则向下移动图形项virtual void mousePressEvent(QGraphicsSceneMouseEvent *event) override;// 悬停事件函数，设置光标外观和提示virtual void hoverEnterEvent(QGraphicsSceneHoverEvent *event) override;// 右键菜单函数，为图形项添加一个右键菜单virtual void contextMenuEvent(QGraphicsSceneContextMenuEvent *event) override;private:QColor brushColor; // 笔刷颜色
};
#endif // MYITEM_H

myitem.cpp

#include "myitem.h"
#include <QPainter>
#include <QCursor>
#include <QKeyEvent>
#include <QGraphicsSceneHoverEvent>
#include <QGraphicsSceneContextMenuEvent>
#include <QMenu>#define WIDTH 40
#define HEIGHT 40#define POS 20MyItem::MyItem()
{brushColor = Qt::black;setFlag(QGraphicsItem::ItemIsFocusable);setFlag(QGraphicsItem::ItemIsMovable);setAcceptHoverEvents(true);}QRectF MyItem::boundingRect() const
{qreal adjust = 0.5; // 返回上下左右+0.5个像素return QRectF(-POS - adjust, -POS - adjust,WIDTH + adjust, HEIGHT + adjust);
}void MyItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *,QWidget *)
{if (hasFocus()) {painter->setPen(QPen(QColor(255, 255, 255)));} else {painter->setPen(QPen(QColor(100, 100, 100)));}painter->setBrush(brushColor);painter->drawRect(-POS, -POS, WIDTH, HEIGHT);
}void MyItem::mousePressEvent(QGraphicsSceneMouseEvent *e)
{setFocus();// 设置光标为手握下的形状setCursor(Qt::ClosedHandCursor);QGraphicsItem::mousePressEvent(e);
}void MyItem::keyPressEvent(QKeyEvent *event)
{if (Qt::Key_Down == event->key())moveBy(0, 10);else if(Qt::Key_Up == event->key())moveBy(0, -10);else if(Qt::Key_Left == event->key())moveBy(-10, 0);else if(Qt::Key_Right == event->key())moveBy(10, 0);else{}QGraphicsItem::keyPressEvent(event);
}void MyItem::hoverEnterEvent(QGraphicsSceneHoverEvent *)
{// 设置光标为手张开的形状setCursor(Qt::OpenHandCursor);setToolTip("click me");
}void MyItem::contextMenuEvent(QGraphicsSceneContextMenuEvent *event)
{QMenu menu;QAction *moveAction = menu.addAction("move origin");QAction *selectedAction = menu.exec(event->screenPos());if (selectedAction == moveAction) {setPos(0, 0);}
}

myview.h

myview继承QGraphicsView，重新实现了滚轮事件，可对场景进行缩放操作

#ifndef MYVIEW_H
#define MYVIEW_H#include <QObject>
#include <QGraphicsView>class MyView : public QGraphicsView
{Q_OBJECT
public:explicit MyView(QWidget *parent = 0);protected:// 滚轮事件：缩放virtual void wheelEvent(QWheelEvent *event) override;
};
#endif // MYVIEW_H

myview.cpp

#include "myview.h"#include "myview.h"
#include <QKeyEvent>MyView::MyView(QWidget *parent) :QGraphicsView(parent)
{
}void MyView::wheelEvent(QWheelEvent *event)
{if(event->delta() > 0){scale(1.1, 1.1);}else{scale(0.9, 0.9);}// 加上这个，否则在场景和图形项中就没法再接收到该事件了QGraphicsView::wheelEvent(event);
}

调用

main.cpp

#include <QApplication>#include "myitem.h"
#include "myview.h"
#include <QTime>
#include <QtMath>#include <QDebug>int main(int argc, char* argv[ ])
{QApplication app(argc, argv);qsrand(QTime(0, 0, 0).secsTo(QTime::currentTime()));QGraphicsScene scene;// 设置场景尺寸，减少动态渲染scene.setSceneRect(-300, -225, 600, 450);// 创建项for (int i = 0; i < 5; ++i) {MyItem *item = new MyItem;item->setColor(QColor(qrand() % 256, qrand() % 256, qrand() % 256));item->setPos(i * 50 - 100, -50);scene.addItem(item);}// 声明视图MyView view;view.setScene(&scene);// 设置背景刷view.setBackgroundBrush(QBrush(QColor(220, 220, 220)));view.show();return app.exec();
}

效果

显示效果如下：