Qt 重写paintEvent事件划线

可以自定义一个类QtImageLabel继承于QLabel，重写paintEvent事件划线，写文字等。如果用 ui 设计，将 QLabel 控件提升为 QtImageLabel 类型即可。

QtImageLabel.h

protected:void paintEvent(QPaintEvent *) override;

QtImageLabel.cpp

#pragma execution_character_set("utf-8")QtImageLabel::QtImageLabel(QWidget *parent): QLabel(parent)
{setScaledContents(true);setAttribute(Qt::WA_QuitOnClose, false);
} void QtImageLabel::paintEvent(QPaintEvent *e)
{QLabel::paintEvent(e);QPainter painter(this);QRect rect = geometry();int c_x = rect.width() / 2;int c_y = rect.height() / 2;painter.setPen(QPen(Qt::red, 1));painter.drawLine(c_x, 0, c_x, c_y * 2);painter.drawLine(0, c_y, c_x * 2, c_y);painter.drawRect(c_x - 130, c_y - 100, 260, 200);painter.drawEllipse(c_x - 130, c_y - 100, 260, 200);painter.setPen(Qt::green);painter.drawRect(c_x - 200, c_y - 150, 400, 300);painter.setPen(Qt::red);painter.drawText(2*c_x - 50, 20, "字体显示");
}

主界面 QtImageShow.cpp

#include "QtImageShow.h"
#include "ui_QtImageShow.h"
#include "QPixmap"#pragma execution_character_set("utf-8")QtImageShow::QtImageShow(QWidget *parent): QWidget(parent)
{ui = new Ui::QtImageShow();ui->setupUi(this);setWindowTitle("图像显式");setAttribute(Qt::WA_QuitOnClose, false);#if 1// 跟随比例变化ui->label->setScaledContents(true);QPixmap pixmap("./01.png");//pixmap.load("./01.jpg");// 让图片大小适应控件大小, 如果不需要，可以直接显示原图QPixmap s_img = pixmap.scaled(ui->label->size(), Qt::KeepAspectRatio, Qt::SmoothTransformation);//ui->label->setPixmap(s_img);ui->label->setPixmap(pixmap);
#endif
}QtImageShow::~QtImageShow()
{delete ui;
}void QtImageShow::paintEvent(QPaintEvent * e)
{
}// 按钮，切换图片显示 01.png 02.png
void QtImageShow::on_pushButton_clicked()
{static int img_id{ 0 };img_id = img_id = std::abs(img_id - 1);QString path = QString("./0") + QString::number(img_id+1) + ".png";QPixmap pixmap(path);ui->label->setPixmap(pixmap);
}