Qt學習: QPaintEvent和QMouseEvent的簡單程序示例

QMouseEvent下可以被重寫的虛函數: 
1.void mousePressEvent(QMouseEvent *event); //鼠標鍵被按下的事件. 
2.void mouseReleaseEvent(QMouseEvent *event); //鼠標鍵被放開的事件. 
3.void mouseMoveEvent(QMouseEvent *event); //按住鼠標鍵移動的事件. 
4.void mouseDoubleClickEvent(QMouseEvent *event); //鼠標鍵被雙擊的事件.

QMouseEvent類中的重要函數: 
1.QPoint pos(); //返回鼠標相對于父部件的坐標. 
2.QPoint globalPos(); //返回鼠標的全局坐標. 
3.QMouseButton button(); //返回鼠標被點擊的鍵.

“c.cpp”下的代碼:

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

c::~c()
{

}void c::mouseMoveEvent(QMouseEvent *event)
{    //保存鼠標移動的時候的尾坐標.
    end = event->pos();    //用來重繪更新.可以理解為調用paintEvent函數，但不一定是立即調用的.在此程序中可以理解為:馬上更新窗口上顯示的圖像.
    update();
}void c::paintEvent(QPaintEvent *event)
{    //畫一個矩形.
    QPainter painter(this);
    painter.setPen(Qt::red);

    QRect temp(start, end);
    painter.setBrush(Qt::green);
    painter.drawRect(temp);
}void c::mouseReleaseEvent(QMouseEvent *event)
{    //當左鍵釋放后，保存尾坐標.
    if (event->button() == Qt::LeftButton)
    {        this->end = event->pos();
        update();
    }
}void c::mousePressEvent(QMouseEvent *event)
{    //當左鍵被按下時，保存首坐標.并更新重繪.
    if (event->button() == Qt::LeftButton)
    {        //點擊的時候定下初始位置.
        this->start = event->pos();
    }
}123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051

“c.h”的代碼:

#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”下的代碼:

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