#ifndef MyPaint_h__
#define MyPaint_h__

#include <QtWidgets/QWidget>

class MyPaint :public QWidget
{
?? ?Q_OBJECT
public:
?? ?MyPaint(QWidget *parent = nullptr);

?? ?void mousePressEvent(QMouseEvent *event);
?? ?void mouseMoveEvent(QMouseEvent *event);
?? ?void mouseReleaseEvent(QMouseEvent *event);
?? ?void paintEvent(QPaintEvent *event);

private:
?? ?std::vector<std::vector<QPoint>> _lines;

};

#endif // MyPaint_h__

實(shí)現(xiàn)

#include "MyPaint.h"
#include <QPainter>
#include <QMouseEvent>


MyPaint::MyPaint(QWidget *parent):QWidget(parent)
{

}

void MyPaint::mousePressEvent(QMouseEvent *event) //鼠標(biāo)按下的時(shí)候新增加一條線，并記錄起點(diǎn)
{
?? ?std::vector<QPoint> line; ?
?? ?line.push_back(event->pos());
?? ?_lines.push_back(line);
}

void MyPaint::mouseMoveEvent(QMouseEvent *event)//鼠標(biāo)移動(dòng)的時(shí)候新增加點(diǎn)
{
?? ?auto &line = _lines[_lines.size() - 1];
?? ?line.push_back(event->pos());

?? ?update(); //更新，重新繪制窗口，自動(dòng)調(diào)用paintEvent
}

void MyPaint::mouseReleaseEvent(QMouseEvent *event)
{
?? ?auto &line = _lines[_lines.size() - 1];
?? ?line.push_back(event->pos());
}

void MyPaint::paintEvent(QPaintEvent *event) //繪制所有的線
{
?? ?//QPainter painter(this);
?? ?//painter.setPen(QPen(Qt::red, 3, Qt::DashLine));
?? ?//painter.setBrush(Qt::blue);
?? ?//painter.drawRect(QRect(10, 10, 100, 30));
?? ?//painter.drawEllipse(130, 10, 50, 50);
?? ?//painter.drawLine(QLine(200, 10, 300, 20));
?? ?//painter.drawText(QPoint(10, 70), "hello" );
?? ?QPainter painter(this);
?? ?painter.setPen(QPen(Qt::green, 3));
?? ?for (const auto &line : _lines)
?? ?{
?? ??? ?for (int i=0;i<line.size()-1;i++)
?? ??? ?{
?? ??? ??? ?painter.drawLine(line.at(i), line.at(i + 1));
?? ??? ?}
?? ?}
}

效果