使用QScatterSeries绘制散点图 出现0xC0000005异常

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如题，我在用QScatterSeries绘制散点图时，想实现点击选中这个点，再次点击取消选中的功能
思路：用了两个series（颜色不同，用来区别选中和未选中的状态）
series1绘制出散点图，点击series1上的点就在series1HandleClickedPoint(const QPointF &point)方法中将点从series1中remove，在series2中append，实现选中的效果
然后在点击series2上的点就在series2HandleClickedPoint(const QPointF &point)方法中将点从series2中remove，在series1中append，实现取消选中的效果
运行时出现异常，疑是出现空指针，但是实在不知道该咋改，求C++大神助力！代码和异常如下：

1. #include "millionpoints.h"
   
2. #include <QtCore/QtMath>
   
3. 
   
4. using namespace QtCharts;
   
5. 
   
6. MillionPoints::MillionPoints(QWidget *parent)
   
7.     : QGraphicsView(parent)
   
8. {
   
9. 
   
10.     series1 = new QScatterSeries();
    
11.     series2 = new QScatterSeries();
    
12.     series1->setName("scatter1");
    
13.     series2->setName("scatter2");
    
14.     series1->setMarkerShape(QScatterSeries::MarkerShapeCircle);
    
15.     series1->setMarkerSize(15.0);
    
16.     for(double i=0; i<100; i+=5)
    
17.     {
    
18.          series1->append(i,sin(i));
    
19.     }
    
20. 
    
21.     chart = new QChart();
    
22.     chart->addSeries(series1);
    
23.     chart->addSeries(series2);
    
24.     chart->createDefaultAxes();
    
25.     chart->axisX()->setRange(0,100);
    
26.     chart->axisY()->setRange(-10,10);
    
27. 
    
28.     scene = new QGraphicsScene();
    
29.     scene->addItem(chart);
    
30.     scene->setSceneRect(0, 0, 800, 500);
    
31.     chart->setGeometry(0,0,800,500);
    
32.     this->setWindowTitle("MillionPoints");
    
33.     this->resize(900,600);
    
34.     this->setScene(scene);
    
35. 
    
36.     connect(series1,SIGNAL(clicked(QPointF)),this,SLOT(series1HandleClickedPoint(QPointF)));
    
37.     connect(series2,SIGNAL(clicked(QPointF)),this,SLOT(series2HandleClickedPoint(QPointF)));
    
38. }
    
39. 
    
40. MillionPoints::~MillionPoints()
    
41. {
    
42. 
    
43. }
    
44. 
    
45. void MillionPoints::series1HandleClickedPoint(const QPointF &point)
    
46. {
    
47.     QPointF clickedPoint = point;
    
48.     if(series2->count()==0){
    
49.         series1->remove(clickedPoint);
    
50.         series2->append(clickedPoint);
    
51.         qDebug()<<"--first click";
    
52.     }else{
    
53.         series1->append(series2->points());
    
54.         series2->clear();
    
55.         series2->append(clickedPoint);
    
56.         series1->remove(clickedPoint);
    
57.         qDebug()<<"--click another point";
    
58.     }
    
59. }
    
60. void MillionPoints::series2HandleClickedPoint(const QPointF &point)
    
61. {
    
62.     QPointF clickedPoint = point;
    
63.     series1->append(clickedPoint);
    
64.     series2->remove(clickedPoint);
    
65.     qDebug()<<"--click last point";
    
66. }

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