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1 介绍

        事件过滤器是一种机制，当某个QObject没有所需要的事件功能时，可将其委托给其它QObject，通过eventFilter成员函数来过滤实现功能。

2 主要构成

委托：

ui->QObject1->installEventFilter(QObject2);

eventFilter声明

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

        在Qt creator中，可以使用如下步骤简化实现：

        a）右键widget

 

        b）选择insert  Virtual。。。：

        c）选择eventFilter，并勾选如下，稍后将定义粘贴到对应的.cpp文件中即可

 3 示例代码：使用事件过滤器对label实现单双击事件响应

       widget.cpp

#include "widget.h"
#include "ui_widget.h"
#include <QEvent>
Widget::Widget(QWidget *parent): QWidget(parent), ui(new Ui::Widget)
{ui->setupUi(this);//将label委托给widgetui->labelSC->setText("单击我");ui->labelSC->installEventFilter(this);ui->labelDC->installEventFilter(this);
}Widget::~Widget()
{delete ui;
}bool Widget::eventFilter(QObject *watched, QEvent *event)
{if(watched == ui->labelSC){if(event->type() == QEvent::Enter)ui->labelSC->setStyleSheet("background-color:rgb(170,255,255)");else if(event->type() == QEvent::Leave){ui->labelSC->setText("单击我");ui->labelSC->setStyleSheet("");}else if(event->type() == QEvent::MouseButtonPress)ui->labelSC->setText("MouseButtonPress");else if(event->type() == QEvent::MouseButtonRelease)ui->labelSC->setText("MouseButtonRelease");}if(watched == ui->labelDC){if(event->type() == QEvent::Enter)ui->labelDC->setStyleSheet("background-color:rgb(170,0,255)");else if(event->type() == QEvent::Leave){ui->labelDC->setText("双击我");ui->labelDC->setStyleSheet("");}else if(event->type() == QEvent::MouseButtonDblClick)ui->labelDC->setText("MouseButtonDblClick");else if(event->type() == QEvent::MouseButtonRelease)ui->labelDC->setText("MouseButtonRelease");}return QWidget::eventFilter(watched, event);
}

        widget.h

#ifndef WIDGET_H
#define WIDGET_H#include <QWidget>QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACEclass Widget : public QWidget
{Q_OBJECTpublic:Widget(QWidget *parent = nullptr);~Widget();private:Ui::Widget *ui;// QObject interface
public:virtual bool eventFilter(QObject *watched, QEvent *event) override;
};#endif // WIDGET_H