其实这个问题，原因是QGraphicsItem的boundingRect的范围不在当前的View范围内，当然不会刷新，特别是自定义的一些Item，特别要注意自己的boundingrect是否在准确的位置，所以其实是boundingrect没有自动更新位置导致的。

当遇到相似的问题时，不妨把boundingrect画出来就可以见分晓了。
下面是我们的代码：

#ifndef LIDARPOINTS_H
#define LIDARPOINTS_H


#include <QColor>
#include <QGraphicsItem>
#include <QImage>

class Lidarpoints : public QGraphicsItem
{
public:
    Lidarpoints(const QColor &color, int x, int y);
    Lidarpoints(/*const QImage image*/);

    void setLidarData(QPoint pos, std::vector<QPoint>& data);

    QRectF boundingRect() const Q_DECL_OVERRIDE;
    QPainterPath shape() const Q_DECL_OVERRIDE;
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *item, QWidget *widget) Q_DECL_OVERRIDE;



protected:
    void mousePressEvent(QGraphicsSceneMouseEvent *event) Q_DECL_OVERRIDE;
    void mouseMoveEvent(QGraphicsSceneMouseEvent *event) Q_DECL_OVERRIDE;
    void mouseReleaseEvent(QGraphicsSceneMouseEvent *event) Q_DECL_OVERRIDE;

private:
    int x;
    int y;
    QColor color;
    QVector<QPointF> stuff;

    //
    QImage imageContent;

    std::vector<QPoint> lidar_points;

    bool paint_state = false;

    int rect_value = 100;

    QRectF paintRect;
};

#endif // LIDARPOINTS_H

#include "lidarpoints.h"
#include <QtWidgets>
#include <iostream>

Lidarpoints::Lidarpoints(const QColor &color, int x, int y)
{
    this->x = x;
    this->y = y;
    this->color = color;
    //
    //setZValue(1000);

    setFlags(ItemIsSelectable | ItemIsMovable);
    setAcceptHoverEvents(true);

    //QSize size(20,20);
    paintRect.setRect(0,0,20,20);
}

Lidarpoints::Lidarpoints(/*const QImage image*/)
{
    //this->imageContent = image;
}


QRectF Lidarpoints::boundingRect() const
{
    //return paintRect;
    return paintRect;

}

QPainterPath Lidarpoints::shape() const
{
    QPainterPath path;
    path.addRect(14, 14, 82, 42);
    return path;
}

void Lidarpoints::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    Q_UNUSED(widget);

    const qreal lod = option->levelOfDetailFromTransform(painter->worldTransform());

    std::cout << "lod " << lod << std::endl;

    //QRect rect(0,0,imageContent.width(),imageContent.height());

    //painter->setCompositionMode(QPainter::CompositionMode_Overlay);

    //painter->drawImage(rect,imageContent);

    //painter->setPen(QPen(Qt::blue,4));//设置画笔形式
    //painter->drawRect(rect);
     //painter->drawEllipse(QPoint(0,0),20,20);//画圆
    std::cout << "paint now" << std::endl;

    QPen pen;
    pen.setColor(Qt::red);  // 画笔颜色设置
    //pen.setWidth(10);
    painter->setPen(pen);

    for(auto it : lidar_points){
        painter->drawPoint(it.x(), -1*it.y());
    }


    //QRect rect(0,0,rect_value,rect_value);
    //painter->drawRect(rect);
    //rect_value+=1;
    //std::cout << "rect_value " << rect_value << std::endl;

    /*
    QRectF rect = boundingRect();

    std::cout << "rect " << rect.x()
                      << "  " << rect.y()
                      << "  " << rect.width()
                      << "  " << rect.height()
                      << std::endl;
    painter->drawRect(rect);
    */

    paint_state = true;

}

void Lidarpoints::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
    QGraphicsItem::mousePressEvent(event);
    update();
}

void Lidarpoints::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
{
    //
    //prepareGeometryChange();

    if (event->modifiers() & Qt::ShiftModifier) {
        stuff << event->pos();
        update();
        return;
    }
    QGraphicsItem::mouseMoveEvent(event);
}

void Lidarpoints::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
{
    QGraphicsItem::mouseReleaseEvent(event);
    update();
}

void Lidarpoints::setLidarData(QPoint pos,  std::vector<QPoint>& data){


    paintRect.setRect(pos.x(), pos.y(),20,20);
    prepareGeometryChange();
    //boundingRect();

    if(paint_state == true){
        std::cout << "Lidarpoints::setLidarData " << lidar_points.size() << std::endl;
        lidar_points.clear();
        lidar_points = data;
    }
    else{

        //std::cout << "auto paint fail " << std::endl;
       // lidar_points.clear();
        //lidar_points = data;
        // 调用此函数以告知 Qt 几何形状即将改变
        //prepareGeometryChange();
        //update();

    }

        paint_state = false;

}

大家可以做个参考。