Qt 事件处理

class QtWidgetsApplication1 : public QMainWindow
{
    Q_OBJECT

public:
    QtWidgetsApplication1(QWidget *parent = nullptr);
    ~QtWidgetsApplication1();

private:
    Ui::QtWidgetsApplication1Class ui;

public slots:
    void changelabel();
};



QtWidgetsApplication1::QtWidgetsApplication1(QWidget *parent)
    : QMainWindow(parent)
{
    ui.setupUi(this);
    QObject::connect(ui.pushButton, SIGNAL(pressed()),this, SLOT(changelabel()));

}

void QtWidgetsApplication1::changelabel()
{
    ui.label->setText(QString("clicked"));
}

class GlobalEventFilter : public QObject
{

public:
    virtual bool eventFilter(QObject* watched, QEvent* event) override
    {
        qDebug() << "watched : " << watched << " event :  " << event->type();
        return false;
    }
};
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QtWidgetsApplication1 w;
    a.installEventFilter(new GlobalEventFilter());
    w.show();
    return a.exec();
}