extern bool isline; //在类声明之前，先声明全局变量，方便在主窗口调用extern bool iscircle;

private:QPushButton *line,*circle; //图形按钮选择QPushButton *finish; //绘图完成void Line();  //实现按钮函数void Circle();void Finish();

bool isline=false;  bool iscircle=false; //全局变量赋值
MainWindow::MainWindow(QWidget *parent) :QMainWindow(parent),ui(new Ui::MainWindow)
{ui->setupUi(this);resize(1200,1000);//设置窗口大小line=new QPushButton("线",this); circle=new QPushButton("圆",this);finish=new QPushButton("完成",this);line->setGeometry(0,80,50,30);circle->setGeometry(0,110,50,30);finish->setGeometry(0,170,50,30);connect(line,&QPushButton::clicked,this,&MainWindow2::Line);connect(circle,&QPushButton::clicked,this,&MainWindow2::Circle);connect(finish,&QPushButton::clicked,this,&MainWindow2::Finish);Scene *scene=new Scene;  //自定义sceneMyview *view=new Myview;  //自定义viewQGridLayout *lay=new QGridLayout;view->setScene(scene);setCentralWidget(view);view->setGeometry(50,50,1000,800);view->translate(QPoint(-500,400));lay->addWidget(view);
}
void MainWindow::Line(){isline=true;   iscircle=false;
}
void MainWindow::Circle(){iscircle=true;   isline=false;
}
void MainWindow::Finish(){isline=iscircle=false;
}

protected:void mouseMoveEvent(QGraphicsSceneMouseEvent *event); //移动void mousePressEvent(QGraphicsSceneMouseEvent *event);//按下void mouseReleaseEvent(QGraphicsSceneMouseEvent *event);//松开
private:QPointF lastpoint,endpoint; //存储鼠标的按下和放开时的坐标

#include "mainwindow.h" //用于调用主窗口的全局变量Scene::Scene(QWidget *parent):QGraphicsScene(parent)
{setSceneRect(-INT_MIN/2,-INT_MIN/2,INT_MAX,INT_MAX); //设置场景边界矩形
}
void Scene::mousePressEvent(QGraphicsSceneMouseEvent *event)
{if(event->button()==Qt::LeftButton){lastpoint=event->scenePos();}endpoint=lastpoint;
}
void Scene::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
{if(event->button()&Qt::LeftButton){endpoint=event->scenePos();update();}
}
void Scene::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
{if(event->button()==Qt::LeftButton){endpoint=event->scenePos();update();if(isline==true){ //接收到按钮信号后进行绘图if(lastpoint!=endpoint){ //避免画点的情况QGraphicsLineItem *line=new QGraphicsLineItem(lastpoint.x(),lastpoint.y(),endpoint.x(),endpoint.y());this->addItem(line);}}if(iscircle==true){qreal r=sqrt(pow((endpoint.x()-lastpoint.x()),2)+pow((endpoint.y()-lastpoint.y()),2));QGraphicsEllipseItem *circle=new QGraphicsEllipseItem(lastpoint.x()-r,lastpoint.y()-r,r*2,r*2);this->addItem(circle);}}
}