Why are so many meaningless readyRead() signals being emitted after I open the same serial port multiple times?

laplacedoge

Here is a SQerialPort object:

QSerialPort serialPort;

And I already connected its readyRead() signal with my SLOT readData():

connect(&serialPort, SIGNAL(readyRead()), this, SLOT(readData()));

And this is what he looks like:

void SerialPort::readData() {
    QByteArray data = serialPort.readAll();
    cout<<"Data("<<data.length()<<"): "<<data.toStdString()<<endl;
    if(data.length()) {
        recvData.append(data);
        if(recvTimer.isActive()) {
            recvTimer.stop();
        }
        recvTimer.singleShot(100, this, SIGNAL(readReadySignal()));
    }
}

There is no problem after the first opening of my serial port, because every time the serial port sender send me data and trigger the readyRead() signal, then I got chunks of data after invoking readAll() , but things are getting worse after I close() the serial port and then open() it again, I received the meaningless readyRead() signal because there is no data(the length of the QByteArray is 0 :( ... ) after I invoke readAll().
After the first opening of serial port:

Data(21): Hello, QT developers!
Data(21): Hello, QT developers!
Data(21): Hello, QT developers!
Data(21): Hello, QT developers!
Data(21): Hello, QT developers!

Second opening:

Data(21): Hello, QT developers!
Data(0): 
Data(21): Hello, QT developers!
Data(0): 
Data(21): Hello, QT developers!
Data(0): 
Data(21): Hello, QT developers!
Data(0):

Third opening:

Data(21): Hello, QT developers!
Data(0): 
Data(0): 
Data(21): Hello, QT developers!
Data(0): 
Data(0): 
Data(21): Hello, QT developers!
Data(0): 
Data(0): 
Data(21): Hello, QT developers!
Data(0): 
Data(0):

Fourth:

Data(21): Hello, QT developers!
Data(0): 
Data(0): 
Data(0): 
Data(0): 
Data(21): Hello, QT developers!
Data(0): 
Data(0): 
Data(0): 
Data(0): 
Data(21): Hello, QT developers!
Data(0): 
Data(0): 
Data(0): 
Data(0):

I didn't invoke readData() from other place, why are so many readyRead() signals being emitted?

JKSH

@laplacedoge said in Why are so many meaningless readyRead() signals being emitted after I open the same serial port multiple times?:

I didn't invoke readData() from other place, why are so many readyRead() signals being emitted?

The readyRead() signal is only emitted once, but your readData() slot gets invoked multiple times. This is because you called QObject::connect() multiple times. Each call creates an additional connection.

The solution? Make sure you only call connect() once, not every time you open the port.

laplacedoge

@JKSH Thanks JKSH, you're are right, I connect() it every time after opening it!

int SerialPort::open(const QString& portName, int baudrate) {
    serialPort.setPortName(portName);
    if(serialPort.open(QIODevice::ReadWrite))
    {
        serialPort.setBaudRate(baudrate);
        serialPort.setDataBits(QSerialPort::Data8);
        serialPort.setParity(QSerialPort::NoParity);
        serialPort.setStopBits(QSerialPort::OneStop);
        serialPort.setFlowControl(QSerialPort::NoFlowControl);
        connect(&serialPort, SIGNAL(readyRead()), this, SLOT(readData())); // NOOO
        return 0;
    }
    return -1;
}