QEvent::MouseButtonPress

​ 鼠标按下时，触发该事件，它对应的子类是QMouseEvent

QEvent::MouseMove

​ 鼠标移动时，触发该事件，它对应的子类是QMouseEvent

QEvent::MouseButtonRelease

​ 鼠标释放时，触发该事件，它对应的子类是QMouseEvent

1 通过自定义控件实现

自定义一个标签控件LabelX，让它继承自QLabel，然后重写父类的mousePressEvent和mouseReleaseEvent 和 mouseMoveEvent。

代码如下：

// 在LabelX.h 中
#ifndef LABELX_H
#define LABELX_H#include <QDebug>
#include <QLabel>
#include <QMouseEvent>class LabelX : public QLabel {Q_OBJECT
public:explicit LabelX(QWidget *parent = nullptr);protected:// 重写父类的方法void enterEvent(QEnterEvent *event);void leaveEvent(QEvent *event);// 按下，移动，释放事件void mousePressEvent(QMouseEvent *event);void mouseReleaseEvent(QMouseEvent *event);void mouseMoveEvent(QMouseEvent *event);signals:
};#endif  // LABELX_H// 在LabelX.cpp 中
#include "labelx.h"LabelX::LabelX(QWidget *parent) : QLabel{parent} {// 实现鼠标的跟踪this->setMouseTracking(true);  // 默认false
}static int cnt = 1;void LabelX::enterEvent(QEnterEvent *event) {Q_UNUSED(event);// qDebug() << "enterEvent: " << cnt++;this->setText(QString("enterEvent: %1").arg(cnt++));
}void LabelX::leaveEvent(QEvent *event) {Q_UNUSED(event);// qDebug() << "leaveEvent: " << cnt++;this->setText(QString("leaveEvent: %1").arg(cnt++));
}void LabelX::mousePressEvent(QMouseEvent *event) {// qDebug() << "mousePressEvent" << event->button() << event->pos()//          << event->globalPosition();if (event->button() == Qt::LeftButton) {qDebug() << "左键按下:"<< "x= " << event->x() << "y= " << event->y();}
}void LabelX::mouseReleaseEvent(QMouseEvent *event) {// qDebug() << "mouseReleaseEvent" << event->button() << event->pos()//          << event->globalPosition();if (event->button() == Qt::LeftButton) {qDebug() << "左键释放:"<< "x= " << event->x() << "y= " << event->y();}
}void LabelX::mouseMoveEvent(QMouseEvent *event) {qDebug() << "mouseMoveEvent" << event->buttons() << event->pos()<< event->globalPosition();if (event->buttons() & Qt::LeftButton) {qDebug() << "左键释放:"<< "x= " << event->x() << "y= " << event->y();}
}

1.1 鼠标跟踪

以上，需要鼠标保持按下的状态下，系统才会调用mouseMoveEvent，实际工作中往往有这么一种需求：

鼠标悬浮在控件上，而不是按下，就触发mouseMoveEvent事件，这怎么实现呢？

答案：设置鼠标跟踪，默认情况下鼠标跟踪是关闭的，需要开启

首先，来到LabelX.cpp中，设置标签使能鼠标跟踪，如下:

LabelX::LabelX(QWidget *parent) : QLabel{parent} {// 实现鼠标的跟踪this->setMouseTracking(true);  // 默认false
}

2 鼠标事件移动标签

// 在press_move_release_widget.h中
#ifndef PRESSMOVERELEASEWIDGET_H
#define PRESSMOVERELEASEWIDGET_H#include <QDebug>
#include <QEvent>
#include <QLabel>
#include <QMouseEvent>
#include <QVBoxLayout>
#include <QWidget>#include "labelx.h"class PressMoveReleaseWidget : public QWidget {Q_OBJECT
public:explicit PressMoveReleaseWidget(QWidget *parent = nullptr);private:QLabel *lbl;QWidget *widget;QPoint pressPos;  // 鼠标按下的位置QPoint wndPos;    // 标签的位置 (左上角的点 top-left)protected:bool eventFilter(QObject *obj, QEvent *event);signals:
};#endif  // PRESSMOVERELEASEWIDGET_H// 在press_move_release_widget.cpp中
#include "press_move_release_widget.h"PressMoveReleaseWidget::PressMoveReleaseWidget(QWidget *parent): QWidget{parent} {QVBoxLayout *verticalLayout = new QVBoxLayout(this);verticalLayout->setSpacing(0);verticalLayout->setContentsMargins(0, 0, 0, 0);// 添加一个自定义控件LabelX *lblx = new LabelX(this);lblx->setText("鼠标按下/移动/释放");lblx->setFrameShape(QFrame::Box);lblx->setFixedHeight(50);lblx->setAlignment(Qt::AlignCenter);lblx->setStyleSheet("background-color: blue; color: white; font-size: 25px");verticalLayout->addWidget(lblx);// 添加一个标准控件widget = new QWidget(this);lbl = new QLabel(widget);lbl->setText("");lbl->setFrameShape(QFrame::Box);lbl->setFixedSize(100, 100);lbl->setStyleSheet("background-color: red;");verticalLayout->addWidget(widget);// 安装事件过滤器lbl->installEventFilter(this);
}bool PressMoveReleaseWidget::eventFilter(QObject *obj, QEvent *event) {if (obj != lbl) {return QWidget::eventFilter(obj, event);}if (event->type() == QEvent::MouseButtonPress) {qDebug() << "MouseButtonPress";// 记录鼠标按下的位置，当前标签的位置QMouseEvent *mouseEvent = static_cast<QMouseEvent *>(event);pressPos = mouseEvent->globalPos();// 标签的位置 (左上角的点 top-left)wndPos = lbl->pos();qDebug() << wndPos;} else if (event->type() == QEvent::MouseMove) {qDebug() << "MouseMove";QMouseEvent *mouseEvent = static_cast<QMouseEvent *>(event);// 标签的位置 + (鼠标当前的位置 - 按下鼠标的位置)// 他们两之差就是鼠标移动的距离QPoint dstPos = wndPos + (mouseEvent->globalPos() - pressPos);lbl->move(dstPos);// 超出了最左边if (lbl->pos().x() < 0) {lbl->move(0, dstPos.y());}// 超出了最右边if (lbl->pos().x() > widget->width() - lbl->width()) {lbl->move(widget->width() - lbl->width(), dstPos.y());}// 超出了最上边if (lbl->pos().y() < 0) {lbl->move(dstPos.x(), 0);}// 超出了最下边if (lbl->pos().y() > widget->height() - lbl->height()) {lbl->move(dstPos.x(), widget->height() - lbl->height());}} else if (event->type() == QEvent::MouseButtonRelease) {qDebug() << "MouseButtonRelease";}
}