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widget
    ui->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_NAMESPACE

class Widget : public QWidget
{
    Q_OBJECT

public:
    Widget(QWidget *parent = nullptr);
    ~Widget();

private:
    Ui::Widget *ui;

    // QObject interface
public:
    virtual bool eventFilter(QObject *watched, QEvent *event) override;
};


#endif // WIDGET_H