事件处理

QT中，事件作为一个对象，继承自QEvent类，常见的有键盘事件QKeyEvent、鼠标事件QMouseEvent和定时器事件QTimerEvent等。QT中，任何QObject子类示例都可以接收和处理事件。实际编程中通常实现部件的paintEvent()、mousePressEvent()等事件处理函数来处理特定部件的特定事件。

每个程序的main函数最后都会调用QApplication类的exec()函数，它会使QT应用程序进入到事件循环，使应用程序在运行的时候接收各种事件。一旦有事件发生，QT便会构造一个相应的QEvent子类的对象来表示它，然后将它传递给QObject对象或子对象。

image-20220219223151174

鼠标事件

对鼠标实现进行重写来实现你想要达到的功能。

mouseevent.h

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#ifndef MOUSEEVENT_H
#define MOUSEEVENT_H

#include <QMainWindow>
#include<QLabel>
#include<QMouseEvent>
namespace Ui {
class MouseEvent;
}

class MouseEvent : public QMainWindow
{
    Q_OBJECT

public:
    explicit MouseEvent(QWidget *parent = 0);
    ~MouseEvent();
protected:
    void mousePressEvent(QMouseEvent *event);//鼠标按下
    void mouseMoveEvent(QMouseEvent *event);//鼠标移动
    void mouseReleaseEvent(QMouseEvent *event);//鼠标释放
private:
    Ui::MouseEvent *ui;
    QLabel *m_statusLabel;
    QLabel* m_posLabel;
};

#endif // MOUSEEVENT_H

mouseevent.cpp

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#include "mouseevent.h"
#include "ui_mouseevent.h"

MouseEvent::MouseEvent(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MouseEvent)
{
    ui->setupUi(this);
    setWindowTitle(QString("鼠标事件"));
    m_statusLabel = new QLabel(QString("当前位置:"));
    m_statusLabel->setFixedWidth(100);

    m_posLabel = new QLabel(QString(""));
    m_posLabel->setFixedWidth(100);

    statusBar()->addPermanentWidget(m_statusLabel);//状态栏添加永久部件
    statusBar()->addPermanentWidget(m_posLabel);
}

MouseEvent::~MouseEvent()
{
    delete ui;
}

void MouseEvent::mousePressEvent(QMouseEvent *event)
{
    QString str = "("+QString::number(event->x())+","+QString::number(event->y())+")";
    if(event->button() == Qt::LeftButton)
    {
        statusBar()->showMessage(QString("左键:") +str );
    }
    else if(event->button() == Qt::MidButton)
    {
        statusBar()->showMessage(QString("中键:")+str);
    }
    else if(event->button() == Qt::RightButton)
    {
        statusBar()->showMessage(QString("右键")+str);
    }
}

void MouseEvent::mouseMoveEvent(QMouseEvent *event)
{
    QString strPos;
    strPos = "(" + QString::number(event->x())+","+QString::number(event->y())+")";
    m_posLabel->setText(strPos);
}

void MouseEvent::mouseReleaseEvent(QMouseEvent *event)
{
    QString strPos;
    strPos = "(" + QString::number(event->x())+","+QString::number(event->y())+")";
    statusBar()->showMessage(QString("释放在:")+strPos,3000);
}

image-20220220112246657

键盘事件

通过重写键盘事件来达到你想要实现的效果。

keyevent.h

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#ifndef KEYEVENT_H
#define KEYEVENT_H

#include <QWidget>
#include<QKeyEvent>
namespace Ui {
class KeyEvent;
}

class KeyEvent : public QWidget
{
    Q_OBJECT

public:
    explicit KeyEvent(QWidget *parent = 0);
    ~KeyEvent();
    void drawPix();
    void keyPressEvent(QKeyEvent *event) override;
    void paintEvent(QPaintEvent* event)override;

private:
    Ui::KeyEvent *ui;
    QPixmap *m_pix;
    QImage m_image;
    int m_startX;      //图标顶点位置
    int m_startY;
    int m_width;       //界面的宽度，高度
    int m_height;
    int m_step;         //步长

};

#endif // KEYEVENT_H

keyevent.cpp

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#include "keyevent.h"
#include "ui_keyevent.h"
#include<QPainter>
#include<QPen>
KeyEvent::KeyEvent(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::KeyEvent)
{
    ui->setupUi(this);
    setWindowTitle(QString("键盘事件"));
    setAutoFillBackground(true);
    setFixedSize(521,256);
    m_width = size().width();
    m_height = size().height();
    m_pix = new QPixmap(m_width,m_height);
    m_pix->fill(Qt::white);
    m_image.load("picture.jpg");
    m_startX = 100;
    m_startY = 100;
    m_step = 20;
    drawPix();

}

KeyEvent::~KeyEvent()
{
    delete ui;
}

void KeyEvent::drawPix()
{
    m_pix->fill(Qt::white);
    QPainter painter(this);
    QPen pen(Qt::DotLine);
    //按照步长画纵向网格线
    //bagin与end成对出现
    for(int i = m_step;i < m_width; i+=m_step)
    {
        painter.begin(m_pix);//指定m_pix为绘图设备
        painter.setPen(pen);//设置笔
        painter.drawLine(QPoint(i,0),QPoint(i,height()));
        painter.end();
    }
    //按照步长画水平网格线
    for(int j = m_step;j < m_height;j += m_step)
    {
        painter.begin(m_pix);//指定m_pix为绘图设备
        painter.setPen(pen);//设置笔
        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，每次移动为1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;
         }
         if(event->key() == Qt::Key_Right)
         {
             m_startX = (m_startX +1+m_image.width()) > m_width ? m_startX :m_startX+1 ;
         }
         if(event->key() == Qt::Key_Up)
         {
            m_startY = (m_startY - 1) < 0 ? m_startY:m_startY -1;
         }
         if(event->key() == Qt::Key_Down)
         {
            m_startY = (m_startY +1 +m_image.height()) > m_height ? m_startY:m_startY+1;
         }
    }
    else//没有按ctrl键，每一移动为一个步长
    {
        //调整图标左上角位置到网格顶点顶点上
        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;
        }
        if(event->key() == Qt::Key_Right)
        {
            m_startX = (m_startX +m_step+m_image.width()) > m_width ? m_startX :m_startX+m_step ;
        }
        if(event->key() == Qt::Key_Up)
        {
           m_startY = (m_startY - m_step) < 0 ? m_startY:m_startY -m_step;
        }
        if(event->key() == Qt::Key_Down)
        {
           m_startY = (m_startY +m_step +m_image.height()) > m_height ? m_startY:m_startY+m_step;
        }
    }
    drawPix();//根据调整后的图标位置重新在m_pix上绘制图像
    update();//触发窗口重绘
}

void KeyEvent::paintEvent(QPaintEvent *event)
{
    QPainter painter;
    painter.begin(this);
    painter.drawPixmap(QPoint(0,0),*m_pix);
    painter.end();
}

image-20220220182327142

事件过滤

指定某个对象对什么事件进行处理。

示例：鼠标按压对指定图片进行缩放

dialog.h

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#ifndef DIALOG_H
#define DIALOG_H

#include <QDialog>
#include<QLabel>
#include<QImage>
#include<QHBoxLayout>
#include<QEvent>
#include<QMouseEvent>

class Dialog : public QDialog
{
    Q_OBJECT

public:
    Dialog(QWidget *parent = 0,Qt::WindowFlags f = 0);
    ~Dialog();
public slots:
    bool eventFilter(QObject*watched ,QEvent *event)override;
private:
    QLabel *m_label1;
    QLabel *m_label2;
    QLabel *m_label3;
    QLabel *m_stateLabel;

    QImage m_image1;
    QImage m_image2;
    QImage m_image3;


};

#endif // DIALOG_H

dialog.cpp

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#include "dialog.h"
#include<QHBoxLayout>

Dialog::Dialog(QWidget *parent,Qt::WindowFlags f)
    : QDialog(parent,f)
{
    setWindowTitle(QString("事件过滤"));

    m_label1 = new QLabel;
    m_label2 =new QLabel;
    m_label3 = new QLabel;
    m_stateLabel = new QLabel(QString("鼠标按下标志"));



    m_stateLabel->setAlignment(Qt::AlignHCenter);//水平居中

    m_image1.load("fly1.png");
    m_image2.load("fly2.png");
    m_image3.load("fly3.png");

    m_label1->setPixmap(QPixmap::fromImage(m_image1));
    m_label2->setPixmap(QPixmap::fromImage(m_image2));
    m_label3->setPixmap(QPixmap::fromImage(m_image3));
    //添加水平布局
    QHBoxLayout *layout = new QHBoxLayout;
    layout->addWidget(m_label1);
    layout->addWidget(m_label2);
    layout->addWidget(m_label3);


    QVBoxLayout*mainLayout = new QVBoxLayout(this);
    mainLayout->addLayout(layout);
    mainLayout->addWidget(m_stateLabel);

    resize(m_image2.width() * 3,m_image2.height() *2);

    //给图片标签部件安装事件过滤，并且指定整个窗体为监视事件的对象。
    m_label1->installEventFilter(this);
    m_label2->installEventFilter(this);
    m_label3->installEventFilter(this);


}

Dialog::~Dialog()
{

}

//对象-事件
bool Dialog::eventFilter(QObject *watched, QEvent *event)
{
    QMatrix matrix;//放大比例
    QImage tmpImg;//保存处理过后的图片

    //放大图片
    matrix.scale(2.0,2.0);
    //对象
    if(watched == m_label1)
    {
        //鼠标按下事件的处理
        if(event->type() == QEvent::MouseButtonPress)
        {
            //转换事件类型Wie鼠标事件
            QMouseEvent* mouseEvent = (QMouseEvent*)event;
            if(mouseEvent->button() & Qt::LeftButton)
            {
                m_stateLabel->setText(QString("左键按下图片1"));
            }
            if(mouseEvent->button() & Qt::MidButton)
            {
                m_stateLabel->setText(QString("中键按下图片1"));
            }
            if(mouseEvent->button() & Qt::RightButton)
            {
                m_stateLabel->setText(QString("右键按下图片1"));
            }
            //将原本图片缩放用tmpImg临时存储，设置图片
            tmpImg = m_image1.transformed(matrix);
            m_label1->setPixmap(QPixmap::fromImage(tmpImg));
        }
        //鼠标释放，恢复图片大小
        if(event->type() == QEvent::MouseButtonRelease)
        {
            m_stateLabel->setText(QString("鼠标释放图片1"));
            m_label1->setPixmap(QPixmap::fromImage(m_image1));
        }
    }
  else if(watched ==m_label2)
  {
        if(event->type() == QEvent::MouseButtonPress)
        {
            QMouseEvent* mouseEvent = (QMouseEvent*)event;
            if(mouseEvent->button() & Qt::LeftButton)
            {
                m_stateLabel->setText(QString("左键按下图片2"));
            }
            if(mouseEvent->button() & Qt::MidButton)
            {
                m_stateLabel->setText(QString("中键按下图片2"));
            }
            if(mouseEvent->button() & Qt::RightButton)
            {
                m_stateLabel->setText(QString("右键按下图片2"));
            }
            tmpImg = m_image2.transformed(matrix);
            m_label2->setPixmap(QPixmap::fromImage(tmpImg));
        }
        if(event->type() == QEvent::MouseButtonRelease)
        {
            m_stateLabel->setText(QString("鼠标释放图片2"));
            m_label2->setPixmap(QPixmap::fromImage(m_image2));
        }
  }
  else if(watched ==m_label3)
  {
      if(event->type() == QEvent::MouseButtonPress)
      {
          QMouseEvent* mouseEvent = (QMouseEvent*)event;
          if(mouseEvent->button() & Qt::LeftButton)
          {
              m_stateLabel->setText(QString("左键按下图片3"));
          }
          if(mouseEvent->button() & Qt::MidButton)
          {
              m_stateLabel->setText(QString("中键按下图片3"));
          }
          if(mouseEvent->button() & Qt::RightButton)
          {
              m_stateLabel->setText(QString("右键按下图片3"));
          }
          tmpImg = m_image3.transformed(matrix);
          m_label3->setPixmap(QPixmap::fromImage(tmpImg));
      }
      if(event->type() == QEvent::MouseButtonRelease)
      {
          m_stateLabel->setText(QString("鼠标释放图片3"));
          m_label3->setPixmap(QPixmap::fromImage(m_image3));
      }
  }

    //事件交给上层对话框进行处理
    return QDialog::eventFilter(watched,event);
}