C++ 错误 : because the following virtual functions are pure within

Question

我在分配类中的对象时遇到问题。感觉我做对了，但它不让我跑。我已经查过了，但我无法弄清楚我做错了什么或与其他人不同。我已经注释掉了一堆东西，但它仍然无法运行

步枪.h

#ifndef rifle_H
#define rifle_H

#include <QPainter>
#include <QGraphicsItem>
#include <QGraphicsScene>

#include <QTimer>
#include <QDialog>

class rifle : public QGraphicsItem
{
public:
    rifle();//(qreal dirx, qreal diry);
    //virtual ~rifle();
    void move();
protected:

private:
    //QPixmap shot;
    qreal m_Speed;
    qreal m_DirX;
    qreal m_DirY;
};

#endif // rifle_H

步枪.cpp

#include "rifle.h"

rifle::rifle() //qreal dirx, qreal diry
//    : m_Speed(5.0)
//    , m_DirX(dirx)
//    , m_DirY(diry)
{
    //shot.load(":/pic/rifle.png");
}

rifle::~rifle()
{

}


void rifle::move()
{
    setPos(x()+m_Speed*m_DirX, y()+m_Speed*m_DirY);
}

这里是我写代码的地方

void Dialog::fire()
{
    qreal dirx = ui->graphicsView->m_FireTarget.x()-200.0;
    qreal diry = ui->graphicsView->m_FireTarget.y()-200.0;

    qreal length = sqrt(dirx*dirx+diry*diry);
    if (length!=0)
    {
        // normalized direction vector
        qreal invLength= 1.0/length;
        dirx *= invLength;
        diry *= invLength;

        // creating an angle perturbation of +/- 3°
        qreal alphaPerturbation = static_cast<qreal>(qrand()%6-3) * M_PI / 180.0;
        qreal xPerturbation = cos(alphaPerturbation);
        qreal yPerturbation = sin(alphaPerturbation);
        // cos(a+b)=...
        dirx = dirx*xPerturbation - diry*yPerturbation;
        // sin(a+b)=...
        diry = diry*xPerturbation + dirx*yPerturbation;

        /*rifle**/ circle = new rifle(dirx, diry);
        scene->addItem(circle);
    }
}

Answer 1

http://qt-project.org/doc/qt-4.8/qgraphicsitem.html

To write your own graphics item, you first create a subclass of QGraphicsItem, and then start by implementing its two pure virtual public functions: boundingRect(), which returns an estimate of the area painted by the item, and paint(), which implements the actual painting.

您必须在 rifle 中覆盖这些函数，因为它们是基类中的纯虚函数。