Qt5学习笔记（消息过滤器）

T06EventFilter.pro

HEADERS += 
    MyWidget.h

SOURCES += 
    MyWidget.cpp

QT += widgets gui

MyWidget.h

#ifndef MYWIDGET_H
#define MYWIDGET_H

#include <QWidget>
#include <QPushButton>
class MyWidget : public QWidget
{
    Q_OBJECT
public:
    explicit MyWidget(QWidget *parent = nullptr);
    QPushButton* _button;
    bool eventFilter(QObject *, QEvent *);//原型
signals:

public slots:
};

#endif // MYWIDGET_H

MyWidget.cpp

#include "MyWidget.h"
#include <QPushButton>
#include <QEvent>
MyWidget::MyWidget(QWidget *parent) : QWidget(parent)
{
    QPushButton* button;
    button = new QPushButton("This button", this);
    connect(button, SIGNAL(clicked()), this, SLOT(close()));

    _button = button;
    /*button给自己安装了一个消息过滤器，经过button的消息，都先要调用它的过滤器eventFilter函数*/
    button->installEventFilter(this);
}

bool MyWidget::eventFilter(QObject *o, QEvent *e)//o谁的，e什么消息(对象，事件)
{

    //(对象，事件)
    if (o == (QObject*)_button &&
            (e->type() == QEvent::MouseButtonPress ||
            e->type() == QEvent::MouseButtonRelease ||
             e->type() == QEvent::MouseButtonRelease ))//截断,单击，双击，不发生反应
    {
        return true;
    }

    return QWidget::eventFilter(o, e);
}
#include <QApplication>
int main(int argc, char* argv[])
{
    QApplication app(argc, argv);

    MyWidget w;
    w.show();

    return app.exec();
}

消息被过滤，单击，双击都没有反应。

如果将１７～２６行注释，单击按钮后，窗口立即消失。

notify：

MyApplication.h

#ifndef MYAPPLICATION_H
#define MYAPPLICATION_H

#include <QApplication>

class MyApplication : public QApplication
{
    Q_OBJECT
public:

    MyApplication(int argc, char* argv[]):QApplication(argc, argv)
    {}
    bool notify(QObject *, QEvent *);
signals:

public slots:
};

#endif // MYAPPLICATION_H

MyWidget.h

#ifndef MYWIDGET_H
#define MYWIDGET_H

#include <QWidget>
#include <QPushButton>
class MyWidget : public QWidget
{
    Q_OBJECT
public:
    explicit MyWidget(QWidget *parent = nullptr);
    QPushButton* _button;
    bool eventFilter(QObject *, QEvent *);//原型
    bool event(QEvent *);//重载event函数
signals:

public slots:
};

#endif // MYWIDGET_H

MyApplication.cpp

#include "MyApplication.h"
#include <QEvent>
#include <QDebug>

bool MyApplication::notify(QObject *o, QEvent *e)
{
    if (this->topLevelWidgets().count()>0)//判断子窗口是否存在
    {
       QWidget* mainWnd = this->topLevelWidgets().at(0);//主窗口不在了，还会notify，会报错，需先判断
       if (o == (QObject*)mainWnd && e->type() == QEvent::MouseButtonPress)
       {
           qDebug() << "mainwnd is clicked";
       }
   }
   return QApplication::notify(o, e);
}

MyWidget.cpp

#include "MyWidget.h"
#include <QPushButton>
#include <QEvent>
#include "MyApplication.h"
#include <QDebug>
MyWidget::MyWidget(QWidget *parent) : QWidget(parent)
{
    QPushButton* button;
    button = new QPushButton("This button", this);
    connect(button, SIGNAL(clicked()), this, SLOT(close()));

    _button = button;
    /*button给自己安装了一个消息过滤器，经过button的消息，都先要调用它的过滤器eventFilter函数*/
    button->installEventFilter(this);
}

bool MyWidget::eventFilter(QObject *o, QEvent *e)//o谁的，e什么消息(对象，事件)
{

    //(对象，事件)
    if (o == (QObject*)_button &&
            (e->type() == QEvent::MouseButtonPress ||
            e->type() == QEvent::MouseButtonRelease ||
             e->type() == QEvent::MouseButtonRelease ))//截断,单击，双击，不发生反应
    {
        return true;
    }

    return QWidget::eventFilter(o, e);
}

bool MyWidget::event(QEvent *e)
{
    if (e->type() == QEvent::User)
    {
       qDebug() << "User event is comming";
    }
    return QWidget::event(e);
}

int main(int argc, char* argv[])
{
    MyApplication app(argc, argv);

    MyWidget w;
    w.show();
    //发送一个Event给MyWidget
    qDebug() << "begin send";
    //发给自定义消息给窗口
    app.postEvent(&w, new QEvent(QEvent::User));//不是立刻处理，加入消息队列等待处理，常用
    app.sendEvent(&w, new QEvent(QEvent::User));//立即处理
    qDebug() << "end send";

    return app.exec();
}

 运行后

第一个User event is comming来自于sendEvent函数，第二个来自于postEvent。

点击主窗口时输出mainwnd is clicked

欢迎交流。