Qt键盘事件实现图片在窗口上下左右移动

#ifndef KEYEVENT_H
#define KEYEVENT_H

#include <QWidget>

QT_BEGIN_NAMESPACE
namespace Ui { class keyEvent; }
QT_END_NAMESPACE

class keyEvent : public QWidget
{
  Q_OBJECT

public:
  keyEvent(QWidget *parent = nullptr);
  ~keyEvent();
  void drawpix();     //自定义成员函数用来在pixmap上绘制网格线和图片
protected:

  void keyPressEvent(QKeyEvent *event) override;   //重写键盘按下事件
  void paintEvent(QPaintEvent *event) override;    //重写绘图事件

private:
  Ui::keyEvent *ui;
  QPixmap *m_pix;
  QImage m_image;
  int m_startX;  //图标顶点的位置
  int m_startY;
  int m_width;  //界面的宽度和高度
  int m_height;
  int m_step;   //图片移动的步长

};
#endif // KEYEVENT_H

keyEvent::keyEvent(QWidget *parent)
  : QWidget(parent)
  , ui(new Ui::keyEvent)
{
  ui->setupUi(this);
  setWindowTitle("键盘事件");
  setAutoFillBackground(true);
  setFixedSize(512,256);
  m_width=size().width();
  m_height=size().height();

  m_pix=new QPixmap(m_width,m_height);
  m_pix->fill(Qt::white);

  m_image.load("../car.png"); //当前工作目录默认Debug目录下，car.png在上一级目录下
  m_startX=100;
  m_startY=100;
  m_step=20;
  drawPix();
}

void keyEvent::drawPix()
{
  m_pix->fill(Qt::white);
  QPainter painter(this);
  QPen pen(Qt::DotLine); //虚线

  painter.begin(m_pix);  //m_pix为绘图设备
  painter.setPen(pen);

  //按照步长画纵向的网格虚线
  for(int i=m_step;i<m_width;i+=m_step){
    painter.drawLine(QPoint(i,0),QPoint(i,m_height));

  }
  //按照步长画横向的网格虚线
  for(int j=m_step;j<m_height;j+=m_step){
    painter.drawLine(QPoint(0,j),QPoint(m_width,j));
  }
  painter.end();

  //画图片
  painter.begin(m_pix);
  painter.drawImage(QPoint(m_startX,m_startY),m_image);
  painter.end();
}

void keyEvent::keyPressEvent(QKeyEvent *event)
{
  //按下ctrl键移动一个像素
  if(event->modifiers()==Qt::ControlModifier){
    if(event->key()==Qt::Key_Left){
      m_startX=(m_startX-1)<0?m_startX:m_startX-1;
    }else if(event->key()==Qt::Key_Right){
      m_startX=(m_startX+1+m_image.width())>m_width?m_startX:m_startX+1;
    }else if(event->key()==Qt::Key_Up){
      m_startY=(m_startY-1)<0?m_startY:m_startY-1;
    }else if(event->key()==Qt::Key_Down){
      m_startY=(m_startY+1+m_image.height())>m_height?m_startY:m_startY+1;
    }
  }else{
    //调整图片左上角的位置到网格顶点
    m_startX=m_startX+m_startX%m_step;
    m_startY=m_startY+m_startY%m_step;
    if(event->key()==Qt::Key_Left){
      m_startX=(m_startX-m_step)<0?m_startX:m_startX-m_step;
    }else if(event->key()==Qt::Key_Right){
      m_startX=(m_startX+m_step+m_image.width())>m_width?m_startX:m_startX+m_step;
    }else if(event->key()==Qt::Key_Up){
      m_startY=(m_startY-m_step)<0?m_startY:m_startY-m_step;
    }else if(event->key()==Qt::Key_Down){
      m_startY=(m_startY+m_step+m_image.height())>m_height?m_startY:m_startY+m_step;
    }
  }
  drawPix(); //刷新图片的位置
  update();//触发窗口重绘 ,执行paintEvent();

}

void keyEvent::paintEvent(QPaintEvent *event)
{
  //定义Qpainter对象，设置窗口为绘图设备，在窗口绘制pixmap
  QPainter painter;
  painter.begin(this);//绘图设备为窗口
  painter.drawPixmap(QPoint(0,0),*m_pix);
  painter.end();


}