Qt学习: QPaintEvent和QMouseEvent的简单程序示例

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)
{
if (sign)
{
//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();
sign = false;
}
}

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();
sign = true;
}
}

“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_OBJECT

public:
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;
bool sign = false;
};

#endif // C_H

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();
}