Code works using waitForReadyRead(), doesn't work when connecting slot to readyRead()

Alexander Wilms

I'm trying to read data from a serial connection.

When I'm using a blocking function, the data is read and processed correctly but I can't display it in the GUI. So I tried reading the data like it's done in the Command Line Reader Async Example. But handleReadyRead() is never called and I don't know why. I'm new to Qt, so I might have overlooked something fundamental.

void Window::read()
{
    QSerialPort serialPort;
    serialPort.setPortName("COM4");

    serialPort.open(QIODevice::ReadOnly);

    // omitted some serial port configuration

    //    while(1)
    //    {
    //        if(serialPort.waitForReadyRead(1000))
    //        {
    //            //Data was returned
    //            QByteArray input = serialPort.readAll();
    //            //qDebug()<<"Response: "<< input;
    //            QList<QByteArray> extracted = input.split('\n');
    //            //qDebug()<<"Response: "<< extracted;
    //            qDebug()<<"Response: "<< extracted.at(1);
    //        }
    //    }

    connect(&serialPort, SIGNAL(readyRead()), this, SLOT(handleReadyRead()));
}


void Window::handleReadyRead()
{
    QByteArray input = serialPort.readAll();
    //qDebug()<<"Response: "<< input;
    QList<QByteArray> extracted = input.split('\n');
    //qDebug()<<"Response: "<< extracted;
    qDebug()<<"Response: "<< extracted.at(1);
}

mrdebug

I suggest you to use waitForReadyRead() in a thread without the events approach.
If you don't want to use threads please use readyRead() event without waitForReadyRead().

Alexander Wilms

Thanks, I'll try usig threads.

SGaist

Hi and welcome to devnet,

There's no need for threads here. What happens is that you declare serialPort in your read function thus it's a local variable that will be destroyed at the end of the function.