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.hmyview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_OBJECTpublic: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：
自定义图形视图
