QMouseEvent下可以被重写的虚函数: 
1.void mousePressEvent(QMouseEvent *event); //鼠标键被按下的事件. 
2.void mouseReleaseEvent(QMouseEvent *event); //鼠标键被放开的事件. 
3.void mouseMoveEvent(QMouseEvent *event); //按住鼠标键移动的事件. 
4.void mouseDoubleClickEvent(QMouseEvent *event); //鼠标键被双击的事件.

QMouseEvent类中的重要函数: 
1.QPoint pos(); //返回鼠标相对于父部件的坐标. 
2.QPoint globalPos(); //返回鼠标的全局坐标. 
3.QMouseButton button(); //返回鼠标被点击的键.

“c.cpp”下的代码:

#include "c.h"c::c(QWidget *parent)
    : QMainWindow(parent)
{
    ui.setupUi(this);
}

c::~c()
{

}void c::mouseMoveEvent(QMouseEvent *event)
{    //保存鼠标移动的时候的尾坐标.
    end = event->pos();    //用来重绘更新.可以理解为调用paintEvent函数，但不一定是立即调用的.在此程序中可以理解为:马上更新窗口上显示的图像.
    update();
}void c::paintEvent(QPaintEvent *event)
{    //画一个矩形.
    QPainter painter(this);
    painter.setPen(Qt::red);

    QRect temp(start, end);
    painter.setBrush(Qt::green);
    painter.drawRect(temp);
}void c::mouseReleaseEvent(QMouseEvent *event)
{    //当左键释放后，保存尾坐标.
    if (event->button() == Qt::LeftButton)
    {        this->end = event->pos();
        update();
    }
}void c::mousePressEvent(QMouseEvent *event)
{    //当左键被按下时，保存首坐标.并更新重绘.
    if (event->button() == Qt::LeftButton)
    {        //点击的时候定下初始位置.
        this->start = event->pos();
    }
}123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051

“c.h”的代码:

#ifndef C_H#define C_H#include <QtWidgets/QMainWindow>#include "ui_c.h"#include <QPixmap>#include <QMouseEvent>#include <QMessageBox>#include <QPainter>#include <QPaintEvent>#include <QVector>class c : public QMainWindow
{
    Q_OBJECTpublic:    c(QWidget *parent = 0);
    ~c();protected:    void mouseMoveEvent(QMouseEvent *event);    void mouseReleaseEvent(QMouseEvent *event);    void mousePressEvent(QMouseEvent *event);    void paintEvent(QPaintEvent *event);private:
    Ui::cClass ui;
    QPoint start;
    QPoint end;
};#endif // C_H1234567891011121314151617181920212223242526272829303132

最后是”main.cpp”下的代码:

#include "c.h"#include <QtWidgets/QApplication>int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    c w;
    w.show();    return a.exec();
}