QtModbus Help

Hi guys, I need someone help to resolve my problem, I've created a program which connect with QtModbus via TCP to the server.
For prototype I use slave program created From qt which is connected on 127.0.0.1 port 502

with this code:

Code:

---

modbusDevice = new QModbusTcpClient(this);
    modbusDevice->setConnectionParameter(QModbusDevice::NetworkAddressParameter, "127.0.0.1");
    modbusDevice->setConnectionParameter(QModbusDevice::NetworkPortParameter, 502);
    if(!modbusDevice->connectDevice()){
        ui->lbl_result->setText("Error");
        return false;
    }

---

The program continue so I suppose that connection work

next I need to Read a register, for example Holding Register at address 1 inside the device so I code:

Code:

---

QModbusDataUnit readUnit(QModbusDataUnit::HoldingRegisters, 1, 1);
    if (auto *reply = modbusDevice->sendReadRequest(readUnit, 1)){
        if (!reply->isFinished()){
            connect(reply, &QModbusReply::finished, this, &MainWindow::show_result);
        }else{
            delete reply;
        }
    }else
        ui->lbl_result->setText("Error");
 
    return true;

---

and the show_result function is:

Code:

---

void MainWindow::show_result(){
    auto reply = qobject_cast<QModbusReply *>(sender());
    if (!reply){
        qDebug() << modbusDevice->errorString();
        return;
    }
 
    if (reply->error() == QModbusDevice::NoError){
        const QModbusDataUnit unit = reply->result();
        int startAddress = unit.startAddress();
        int value = unit.value(0);
        qDebug() << startAddress + " valore: " + value;
    }
    else
        ui->lbl_result->setText("Error");
 
    reply->deleteLater();
}

---

But always when this function was called, return an error in the first line: "Device is not connected"

How I can fix this, I try to check all example or someting but i not find error.

Thanks for your help and attention

Are you making sure that you call the read function only after the device object has signalled it is in connected state?

Cheers,
_

I hope yes but... I try to check modbusDevice->state(); and in effect it is afer connection in QModbusDevice::ConnectingState. Maybe i need other instruction for connection, or maybe there is a problem in localhost slave?

Thanks for reply!