Qt鍵盤事件實現圖片在視窗上下左右移動

#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();         //自定義成員函數用來在pixmap上繪製格線和圖片
protected:

    void keyPressEvent(QKeyEvent *event) override;      //重寫鍵盤按下事件
    void paintEvent(QPaintEvent *event) override;       //重寫繪圖事件

private:
    Ui::keyEvent *ui;
    QPixmap *m_pix;
    QImage m_image;
    int m_startX;   //圖示頂點的位置
    int m_startY;
    int m_width;    //介面的寬度和高度
    int m_height;
    int m_step;     //圖片移動的步長

};
#endif // KEYEVENT_H

keyEvent::keyEvent(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::keyEvent)
{
    ui->setupUi(this);
    setWindowTitle("鍵盤事件");
    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"); //當前工作目錄預設Debug目錄下，car.png在上一級目錄下
    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); //虛線

    painter.begin(m_pix);   //m_pix為繪圖裝置
    painter.setPen(pen);

    //按照步長畫縱向的網格虛線
    for(int i=m_step;i<m_width;i+=m_step){
        painter.drawLine(QPoint(i,0),QPoint(i,m_height));

    }
    //按照步長畫橫向的網格虛線
    for(int j=m_step;j<m_height;j+=m_step){
        painter.drawLine(QPoint(0,j),QPoint(m_width,j));
    }
    painter.end();

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

void keyEvent::keyPressEvent(QKeyEvent *event)
{
    //按下ctrl鍵移動一個畫素
    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{
        //調整圖片左上角的位置到網格頂點
        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();  //重新整理圖片的位置
    update();//觸發視窗重繪 ,執行paintEvent();

}

void keyEvent::paintEvent(QPaintEvent *event)
{
    //定義Qpainter物件，設定視窗為繪圖裝置，在視窗繪製pixmap
    QPainter painter;
    painter.begin(this);//繪圖裝置為視窗
    painter.drawPixmap(QPoint(0,0),*m_pix);
    painter.end();


}