HEADERS += \

     MyWidget.h

 SOURCES += \

     MyWidget.cpp

 QT += widgets gui

 #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

 #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();

 }

 #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

 #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

 #include "MyApplication.h"

 #include <QEvent>

 #include <QDebug>

 bool MyApplication::notify(QObject *o, QEvent *e)

 {

     if (this->topLevelWidgets().count()>)//判断子窗口是否存在

     {

        QWidget* mainWnd = this->topLevelWidgets().at();//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);

 }

 #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();

 }