スレッドはメインウィンドウにイベント(メッセージ)を送信し、文字列を渡します.

#ifndef CUSTOMEVENT_H
#define CUSTOMEVENT_H

#include 
#include 

class CustomEvent : public QEvent //      
{
public:
    CustomEvent(const QString & msg);

    static QEvent::Type m_eventType; //       
    static QEvent::Type evType(); //        

    QString m_msg; //          
};

#endif // CUSTOMEVENT_H

#include "CustomEvent.h"

QEvent::Type CustomEvent::m_eventType = (QEvent::Type)QEvent::registerEventType(); //         

CustomEvent::CustomEvent(const QString &msg)
    :QEvent(evType()), m_msg(msg)
{}

QEvent::Type CustomEvent::evType()
{
    return m_eventType;
}

#include "widget.h"
#include 
#include 
#include 
#include 
#include 

//         
class SimpleThread: public QThread
{
public:
    SimpleThread(QObject *receiver)
        : m_receiver(receiver)
    {}

    void run()
    {
        while(1)
        {
            QThread::msleep(1000);
            CustomEvent *ce = new CustomEvent(QDateTime::currentDateTime().toString("yyyy-MM-dd hh:mm:ss"));
            QCoreApplication::postEvent(m_receiver, ce); //              ，             
        }
    }

    QObject *m_receiver; //         
};

//       ：
Widget::Widget(QWidget *parent)
    : QWidget(parent)
{
    m_label = new QLabel(this); //    

    SimpleThread *t = new SimpleThread(this); //               
    t->start(); //     ，    
}

Widget::~Widget()
{

}

bool Widget::event(QEvent *e) //         
{
    if(e->type() == CustomEvent::evType()) //          ，    
    {
        CustomEvent *ce = (CustomEvent*)e;
        m_label->setText(ce->m_msg); // m_label        
        m_label->adjustSize();
        e->accept(); //       ，        
        return true;
    }
    return QWidget::event(e); //        ，          
}