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()>)//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);
 }

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。