通过使用eventFilter 事件过滤器，实现QLabel的 Enter、Leave 、MouseButtonPress、MouseButtonDblClick、MouseButtonRelease

EventFilterExample.h

#ifndef EVENTFILTEREXAMPLE_H
#define EVENTFILTEREXAMPLE_H

#include <QWidget>

namespace Ui {
class EventFilterExample;
}

class EventFilterExample : public QWidget
{
    Q_OBJECT

public:
    explicit EventFilterExample(QWidget *parent = nullptr);
    ~EventFilterExample();

    bool eventFilter(QObject *watched, QEvent *event);

private:
    Ui::EventFilterExample *ui;
};

#endif // EVENTFILTEREXAMPLE_H

EventFilterExample.cpp

#include "eventfilterexample.h"
#include "ui_eventfilterexample.h"

EventFilterExample::EventFilterExample(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::EventFilterExample)
{
    ui->setupUi(this);
    //给label控件安装事件过滤器
    ui->labHover->installEventFilter(this);
    ui->labDoubleClick->installEventFilter(this);
}

EventFilterExample::~EventFilterExample()
{
    delete ui;
}

bool EventFilterExample::eventFilter(QObject *watched, QEvent *event)
{
    if(watched== ui->labHover)
    {
        if(event->type()==QEvent::Enter)
        {
            ui->labHover->setStyleSheet("background-color:rgb(170, 255, 255);");
        }
        else if(event->type()==QEvent::Leave)
        {
            ui->labHover->setStyleSheet("");
            ui->labHover->setText("靠近我，点击我~");
        }
        else if(event->type()== QEvent::MouseButtonPress)
        {
            ui->labHover->setText("Button Pressed");
        }
        else if(event->type()== QEvent::MouseButtonRelease)
            ui->labHover->setText("Button Released");


    }
    if(watched == ui->labDoubleClick)
    {
        if(event->type()== QEvent::Enter)
        {
            ui->labDoubleClick->setStyleSheet("background-color: rgb(85, 255, 127);");
        }
        else if(event->type()==QEvent::Leave)
        {
            ui->labDoubleClick->setStyleSheet("");
            ui->labDoubleClick->setText("可双击的标签");
        }
        else if(event->type()==QEvent::MouseButtonDblClick)
        {
            ui->labDoubleClick->setText("Double Clicked");
        }

    }
    return QWidget::eventFilter(watched,event);
}

效果

总结

需要在构造函数中，给控件安装事件过滤器，才起作用

   //给label控件安装事件过滤器
    ui->labHover->installEventFilter(this);
    ui->labDoubleClick->installEventFilter(this);