Qt工作笔记-视图（QGraphicsView）的放大和缩小（通过滚轮）

程序运行截图如下：

关键的函数:

 

逻辑：通过滚轮事件，识别滚轮放大上移还是下移动，调用这个函数

源码如下：

mygraphicsview.h

#ifndef MYGRAPHICSVIEW_H
#define MYGRAPHICSVIEW_H

#include <QObject>
#include <QGraphicsView>

QT_BEGIN_NAMESPACE
class QWheelEvent;
QT_END_NAMESPACE

class MyGraphicsView : public QGraphicsView
{
    Q_OBJECT
public:
    explicit MyGraphicsView(QWidget *parent = 0);
    ~MyGraphicsView();

protected:
    void wheelEvent(QWheelEvent *event) Q_DECL_OVERRIDE;
    void magnify();
    void shrink();
    void scaling(qreal scaleFactor);

private:
    qreal m_scalingOffset;
};

#endif // MYGRAPHICSVIEW_H

widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

QT_BEGIN_NAMESPACE
class QGraphicsScene;
QT_END_NAMESPACE

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();

private:
    Ui::Widget *ui;
    QGraphicsScene *m_scene;
};

#endif // WIDGET_H

main.cpp

#include "widget.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
    w.show();

    return a.exec();
}

mygraphicsview.cpp

#include "mygraphicsview.h"
#include <QWheelEvent>
#include <QPoint>
#include <QDebug>

MyGraphicsView::MyGraphicsView(QWidget *parent)
    : QGraphicsView(parent)
{
    m_scalingOffset=1;
}

MyGraphicsView::~MyGraphicsView()
{

}

void MyGraphicsView::magnify()
{
    if(m_scalingOffset>1.3)
        return;

    m_scalingOffset+=0.1;
    scaling(m_scalingOffset);
}

void MyGraphicsView::shrink()
{
    if(m_scalingOffset<0.9)
        return;

    m_scalingOffset-=0.1;
    scaling(m_scalingOffset);
}

void MyGraphicsView::scaling(qreal scaleFactor)
{
    qDebug()<<this->sceneRect();
    scale(scaleFactor,scaleFactor);
}

void MyGraphicsView::wheelEvent(QWheelEvent *event)
{
    QPoint sroll=event->angleDelta();
    sroll.y()>0?magnify():shrink();

}

widget.cpp

#include "widget.h"
#include "ui_widget.h"
#include <QGraphicsRectItem>

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);

    m_scene=new QGraphicsScene;
    QGraphicsRectItem *item=new QGraphicsRectItem;
    item->setPos(0,0);
    item->setBrush(QBrush(Qt::red));
    item->setRect(0,0,100,100);
    m_scene->addItem(item);
    ui->graphicsView->setSceneRect(-100,-100,100,100);
    ui->graphicsView->setScene(m_scene);

}

Widget::~Widget()
{
    delete ui;
}