How to emit progressTextChanged (QString) signal in QFutureWatcher?

Having this code is possible to emit the progressTextChanged(QString) signal? i have tried but i when trying to access the signal the compiler says it is protected.

Code:

//...
//...
QFuture<bool> future = QtConcurrent::run( 
        this, 
        &MyClass::runTheTask );
 
    QFutureWatcher<bool> watcher;
    connect( &watcher, SIGNAL( progressTextChanged( const QString ) ), 
             this, SLOT( appendMessageToStatusLineEdit( const QString ) ) );
    watcher.setFuture( future );
    future.waitForFinished();
 
// ...
// ...

Code:

bool MyClass::runTheTask()
{
// do the task
 
 
 
// how to emit progress text signal???
}
 
void MyClass::appendMessageToStatusLineEdit( const QString msg )
{
    QMetaObject::invokeMethod( this, 
                               "doAppendMessageToStatusLineEdit", 
                               Qt::QueuedConnection,
                               Q_ARG( QString, msg ) );
}
 
void MyClass::doAppendMessageToStatusLineEdit( const QString msg )
{
    _ui->statusTextEdit->append( msg );
}