C++ 使用moveBy移动QGraphicsItem

我尝试通过moveBy移动QGraphicsItem框。若我将keyPressEvent放在item类中—它是工作的，但若我将此函数放在mainwindow类中并尝试通过指针调用moveBy函数—它不工作。我做错了什么

项目h：

#ifndef ITEM_H
#define ITEM_H


#include <QGraphicsItem>
#include <QGraphicsView>
#include <QKeyEvent>
class item: public QGraphicsItem
{
public:
  //virtual void keyPressEvent(QKeyEvent *event);

  item(QGraphicsItem *parent =NULL);
  QRectF boundingRect() const;


  protected:
void paint(QPainter *painter, const QStyleOptionGraphicsItem *option,QWidget *widget);
};

#endif // ITEM_H

mainwindow.cpp：

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "QGraphicsScene"
#include "QGraphicsView"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    QGraphicsScene *scene = new QGraphicsScene;
    box = new item;
    scene->addItem(box);
    QGraphicsView *view = new QGraphicsView;
    view->setScene(scene);
    view->show();
}
MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::keyPressEvent(QKeyEvent *event)
{
    switch(event->key())
    {
    case Qt::Key_Right:
         box->moveBy(3,3);
         break;


    case Qt::Key_Left:

         break;


    case Qt::Key_Up:

         break;


     case Qt::Key_Down:


      break;

  }


}

---

您确定您的程序在按键时会进入主窗口：：keyPressEventQKeyEvent*事件吗？试着像qDebug一样调试或放置smth

#include "item.h"

item::item(QGraphicsItem *parent): QGraphicsItem(parent)
{
    setFlag(QGraphicsItem::ItemIsFocusable);
}

QRectF item::boundingRect() const
{
    return QRectF(0,0,200,200);

}

void item::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{

    painter->drawPixmap(1,1, QPixmap(":/Graphics/Untitled.png"));
}

/*
void item::keyPressEvent(QKeyEvent *event)
{
    switch(event->key())
    {
    case Qt::Key_Right:
         moveBy(3,0);
         break;


    case Qt::Key_Left:
         moveBy(-3,0);
         break;


    case Qt::Key_Up:
         moveBy(0,-3);
         break;


     case Qt::Key_Down:
          moveBy(0,3);

      break;

  }


}
*/

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "QGraphicsScene"
#include "QGraphicsView"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    QGraphicsScene *scene = new QGraphicsScene;
    box = new item;
    scene->addItem(box);
    QGraphicsView *view = new QGraphicsView;
    view->setScene(scene);
    view->show();
}
MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::keyPressEvent(QKeyEvent *event)
{
    switch(event->key())
    {
    case Qt::Key_Right:
         box->moveBy(3,3);
         break;


    case Qt::Key_Left:

         break;


    case Qt::Key_Up:

         break;


     case Qt::Key_Down:


      break;

  }


}