程序运行截图如下:
关键:
当处理场景中的图形项时,将坐标或者一个任意的形状从场景映射到图形项、或者从一个图形项映射到另一个图形项、或者从视图映射到场景,这些坐标变换都是很常用的。例如,在QGraphicsView的视口上单击了鼠标,便可调用QGraphicsView::mapToScene()以及QGraphicsScene::itemAt()来获取光标下的图形项;如果要获取一个图形项在视口中的位置,那么可以先在图形项上调用QGraphicsItem::mapToScene(),然后在视图上调用QGraphicsView::mapFromScene();如果要获取在视图的一个椭圆形中包含的图形项,可以先传递一个QPainterPath对象作为参数给mapToScene()函数,然后传递映射后的路径给QGraphicsScene::items()函数。n 不仅可以在视图、场景和图形项之间使用坐标映射,还可以在子图形项和父图形项或者图形项和图形项之间进行坐标映射。
代码如下:
mygraphicsview.h
#ifndef MYGRAPHICSVIEW_H
#define MYGRAPHICSVIEW_H
#include <QGraphicsView>
#include <QObject>
#include <QPoint>
class MyGraphicsView : public QGraphicsView
{
Q_OBJECT
public:
MyGraphicsView(QWidget *parent=0);
~MyGraphicsView();
protected:
void contextMenuEvent(QContextMenuEvent *event);
protected slots:
void removeAction();
private:
QGraphicsItem *m_selectItem;
QPoint m_point;
};
#endif // MYGRAPHICSVIEW_H
widget.h
#ifndef WIDGET_H
#define WIDGET_H
#include <QWidget>
class QGraphicsScene;
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 <QGraphicsScene>
#include <QMenu>
#include <QContextMenuEvent>
#include <QAction>
#include <QDebug>
#include <QTransform>
#include <QGraphicsRectItem>
MyGraphicsView::MyGraphicsView(QWidget *parent):
QGraphicsView(parent)
{
}
MyGraphicsView::~MyGraphicsView()
{
}
void MyGraphicsView::contextMenuEvent(QContextMenuEvent *event)
{
QGraphicsScene *scenpt=this->scene();
QTransform transform;
m_selectItem=scenpt->itemAt(mapToScene(event->pos()),transform);
if(m_selectItem==NULL)
return;
QMenu menu;
menu.addAction("删除",this,&MyGraphicsView::removeAction);
menu.exec(event->globalPos());
}
void MyGraphicsView::removeAction()
{
if(m_selectItem==NULL)
return;
QGraphicsRectItem *item=(QGraphicsRectItem*)m_selectItem;
delete item;
m_selectItem=NULL;
}
widget.cpp
#include "widget.h"
#include "ui_widget.h"
#include <QGraphicsScene>
#include <QBrush>
#include <QGraphicsRectItem>
Widget::Widget(QWidget *parent) :
QWidget(parent),
ui(new Ui::Widget)
{
ui->setupUi(this);
m_scene=new QGraphicsScene(this);
m_scene->setSceneRect(0,0,600,300);
ui->graphicsView->setScene(m_scene);
QGraphicsRectItem *item=new QGraphicsRectItem;
item->setRect(100,100,150,150);
item->setBrush(QBrush(Qt::green));
m_scene->addItem(item);
}
Widget::~Widget()
{
delete ui;
}