Qt--在Label上画矩形

爱被打了一巴掌 2023-07-12 03:36 44阅读 0赞

1、实现方法：

需要继承QLabel并重写以下函数实现：

void mousePressEvent(QMouseEvent *ev);
    void mouseMoveEvent(QMouseEvent *ev);
    void mouseReleaseEvent(QMouseEvent *ev);
    void paintEvent(QPaintEvent *);

2、源代码如下：

mylabel.h

#ifndef MYLABEL_H
    #define MYLABEL_H
    
    #include <QLabel>
    #include <QMouseEvent>
    #include <QDebug>
    #include <QPaintEvent>
    #include <QPainter>
    
    class MyLabel : public QLabel
    { 
        Q_OBJECT
    public:
        explicit MyLabel(QWidget *parent = 0);
    
    protected:
        void mousePressEvent(QMouseEvent *ev);
        void mouseMoveEvent(QMouseEvent *ev);
        void mouseReleaseEvent(QMouseEvent *ev);
    
        void paintEvent(QPaintEvent *);
    
    private:
        int x1;
        int x2;
        int y1;
        int y2;
    };
    #endif // MYLABEL_H

mylabel.cpp

#include "mylabel.h"
    
    MyLabel::MyLabel(QWidget *parent) : QLabel(parent)
    { 
    
    }
    
    void MyLabel::paintEvent(QPaintEvent *)
    { 
        QPainter painter(this);
    
        painter.setPen(QPen(Qt::red, 2));
        painter.drawRect(QRect(x1, y1, x2 - x1, y2 - y1));
    }
    
    void MyLabel::mousePressEvent(QMouseEvent *ev)
    { 
        x1 = ev->x();
        y1 = ev->y();
    }
    
    void MyLabel::mouseMoveEvent(QMouseEvent *ev)
    { 
        x2 = ev->x();
        y2 = ev->y();
        update();
    }
    
    void MyLabel::mouseReleaseEvent(QMouseEvent *ev)
    { 
    
    }

3、效果  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjcwNDA5MA_size_16_color_FFFFFF_t_70]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjcwNDA5MA_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200319085451627.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjcwNDA5MA==,size_16,color_FFFFFF,t_70