事件过滤

事件过滤是当事件发生时，可以对不同对象，实现不同操作，以达到筛选的效果。
步骤：
1、首先安装一个事件过滤器，为对象安装事件过滤，指定“谁”来监控这些事件对象

//给m_label123安装事件过滤，指定(this)当前整个窗体监视我们的事件对象
m_label1->installEventFilter(this);
m_label2->installEventFilter(this);
m_label3->installEventFilter(this);

2、重写bool eventFilter(QObject *obj, QEvent *event)。

//第一个参数是监视对象，第二个参数是事件
bool EventFilter::eventFilter(QObject *watched, QEvent *event)
{QMatrix matrix;QImage tmpImg;//放大图片matrix.scale(2.0,2.0);if(watched == m_label1){//鼠标按下事件if(event->type() == QEvent::MouseButtonPress){QMouseEvent* mouseEvent = (QMouseEvent*)event;if(mouseEvent->buttons()&Qt::LeftButton){m_stateLabel->setText(QStringLiteral("左键按下图片1"));}if(mouseEvent->buttons()&Qt::MidButton){m_stateLabel->setText(QStringLiteral("中键按下图片1"));}if(mouseEvent->buttons()&Qt::RightButton){m_stateLabel->setText(QStringLiteral("右键按下图片1"));}tmpImg = m_image1.transformed(matrix);m_label1->setPixmap(QPixmap::fromImage(tmpImg));}if(event->type()==QEvent::MouseButtonRelease){m_stateLabel->setText(QStringLiteral("鼠标释放图片1"));m_label1->setPixmap(QPixmap::fromImage(m_image1));}}else if(watched == m_label2){//鼠标按下事件if(event->type() == QEvent::MouseButtonPress){QMouseEvent* mouseEvent = (QMouseEvent*)event;if(mouseEvent->buttons()&Qt::LeftButton){m_stateLabel->setText(QStringLiteral("左键按下图片2"));}if(mouseEvent->buttons()&Qt::MidButton){m_stateLabel->setText(QString("中键按下图片2"));}if(mouseEvent->buttons()&Qt::RightButton){m_stateLabel->setText(QString("右键按下图片2"));}tmpImg = m_image2.transformed(matrix);m_label2->setPixmap(QPixmap::fromImage(tmpImg));}if(event->type()==QEvent::MouseButtonRelease){m_stateLabel->setText(QStringLiteral("鼠标释放图片2"));m_label2->setPixmap(QPixmap::fromImage(m_image2));}}else if(watched == m_label3){//鼠标按下事件if(event->type() == QEvent::MouseButtonPress){QMouseEvent* mouseEvent = (QMouseEvent*)event;if(mouseEvent->buttons()&Qt::LeftButton){m_stateLabel->setText(QStringLiteral("左键按下图片3"));}if(mouseEvent->buttons()&Qt::MidButton){m_stateLabel->setText(QStringLiteral("中键按下图片3"));}if(mouseEvent->buttons()&Qt::RightButton){m_stateLabel->setText(QStringLiteral("右键按下图片3"));}tmpImg = m_image3.transformed(matrix);m_label3->setPixmap(QPixmap::fromImage(tmpImg));}if(event->type()==QEvent::MouseButtonRelease){m_stateLabel->setText(QStringLiteral("鼠标释放图片3"));m_label3->setPixmap(QPixmap::fromImage(m_image3));}}//将事件交给上层对话框进行处理return QDialog::eventFilter(watched,event);
}

完整代码

eventfilter.h

#ifndef EVENTFILTER_H
#define EVENTFILTER_H#include <QDialog>
#include <QLabel>
class EventFilter : public QDialog
{Q_OBJECTpublic:EventFilter(QWidget *parent = 0,Qt::WindowFlags f = 0);~EventFilter();
public slots://第一个参数是监视的对象，第二个参数是事件bool eventFilter(QObject*watched,QEvent *event)override;
private://将图片加载到label中QLabel* m_label1;QLabel* m_label2;QLabel* m_label3;QLabel* m_stateLabel;//QImage m_image1;QImage m_image2;QImage m_image3;
};#endif // EVENTFILTER_H

eventfilter.cpp

#include "eventfilter.h"
#include <QPixmap>
#include <QHBoxLayout>
#include <QVBoxLayout>
#include <QEvent>
#include <QMouseEvent>
EventFilter::EventFilter(QWidget *parent,Qt::WindowFlags f): QDialog(parent,f)
{setWindowTitle(QStringLiteral("事件过滤"));m_label1 = new QLabel;m_label2 = new QLabel;m_label3 = new QLabel;m_stateLabel = new QLabel(QStringLiteral("鼠标按下标志"));//加个框框//m_stateLabel->setFrameStyle(QFrame::Box);//设置对齐方式：水平居中m_stateLabel->setAlignment(Qt::AlignHCenter);m_image1.load("./fly1.png");m_image2.load("./fly2.png");m_image3.load("./fly3.png");m_label1->setPixmap(QPixmap::fromImage(m_image1));m_label2->setPixmap(QPixmap::fromImage(m_image2));m_label3->setPixmap(QPixmap::fromImage(m_image3));QHBoxLayout* layout = new QHBoxLayout;layout->addWidget(m_label1);layout->addWidget(m_label2);layout->addWidget(m_label3);QVBoxLayout* mainLayout = new QVBoxLayout(this);mainLayout->addLayout(layout);mainLayout->addWidget(m_stateLabel);resize(m_image2.width() * 3,m_image2.height() * 2);//给m_label123安装事件过滤，指定(this)当前整个窗体监视我们的事件对象m_label1->installEventFilter(this);m_label2->installEventFilter(this);m_label3->installEventFilter(this);}EventFilter::~EventFilter()
{}
//第一个参数是监视对象，第二个参数是事件
bool EventFilter::eventFilter(QObject *watched, QEvent *event)
{QMatrix matrix;QImage tmpImg;//放大图片matrix.scale(2.0,2.0);if(watched == m_label1){//鼠标按下事件if(event->type() == QEvent::MouseButtonPress){QMouseEvent* mouseEvent = (QMouseEvent*)event;if(mouseEvent->buttons()&Qt::LeftButton){m_stateLabel->setText(QStringLiteral("左键按下图片1"));}if(mouseEvent->buttons()&Qt::MidButton){m_stateLabel->setText(QStringLiteral("中键按下图片1"));}if(mouseEvent->buttons()&Qt::RightButton){m_stateLabel->setText(QStringLiteral("右键按下图片1"));}tmpImg = m_image1.transformed(matrix);m_label1->setPixmap(QPixmap::fromImage(tmpImg));}if(event->type()==QEvent::MouseButtonRelease){m_stateLabel->setText(QStringLiteral("鼠标释放图片1"));m_label1->setPixmap(QPixmap::fromImage(m_image1));}}else if(watched == m_label2){//鼠标按下事件if(event->type() == QEvent::MouseButtonPress){QMouseEvent* mouseEvent = (QMouseEvent*)event;if(mouseEvent->buttons()&Qt::LeftButton){m_stateLabel->setText(QStringLiteral("左键按下图片2"));}if(mouseEvent->buttons()&Qt::MidButton){m_stateLabel->setText(QString("中键按下图片2"));}if(mouseEvent->buttons()&Qt::RightButton){m_stateLabel->setText(QString("右键按下图片2"));}tmpImg = m_image2.transformed(matrix);m_label2->setPixmap(QPixmap::fromImage(tmpImg));}if(event->type()==QEvent::MouseButtonRelease){m_stateLabel->setText(QStringLiteral("鼠标释放图片2"));m_label2->setPixmap(QPixmap::fromImage(m_image2));}}else if(watched == m_label3){//鼠标按下事件if(event->type() == QEvent::MouseButtonPress){QMouseEvent* mouseEvent = (QMouseEvent*)event;if(mouseEvent->buttons()&Qt::LeftButton){m_stateLabel->setText(QStringLiteral("左键按下图片3"));}if(mouseEvent->buttons()&Qt::MidButton){m_stateLabel->setText(QStringLiteral("中键按下图片3"));}if(mouseEvent->buttons()&Qt::RightButton){m_stateLabel->setText(QStringLiteral("右键按下图片3"));}tmpImg = m_image3.transformed(matrix);m_label3->setPixmap(QPixmap::fromImage(tmpImg));}if(event->type()==QEvent::MouseButtonRelease){m_stateLabel->setText(QStringLiteral("鼠标释放图片3"));m_label3->setPixmap(QPixmap::fromImage(m_image3));}}//将事件交给上层对话框进行处理return QDialog::eventFilter(watched,event);
}