QTimer in a GUI application

HamiltonQ

I don't initiated any thread purposely. I do not know if the application automatically starts some thread to call some method or to start some object.

HamiltonQ

I just want to start a count to trigger a function every 20 ms in the same class that contains the call to the UI. It's possible?

alex_malyu

It should not be a problem unless doMyTask () can initiate another call to showPorts () in which cay you may keep creating timers until system is exhausted

Alex.

HamiltonQ

[quote author="alex_malyu" date="1421985237"]It should not be a problem unless doMyTask () can initiate another call to showPorts () in which cay you may keep creating timers until system is exhausted

Alex.[/quote]

Thanks, Alex!

But, why doMyTask() have to call showPorts()? I just wanna call doMyTask every 20 ms.

HamiltonQ

I changed of place the connect ( connect (time, SIGNAL (timeout ()), this, SLOT (doMyTask ())); ), I put him on constructor, but nothing changed, I keep getting the output:

QObject :: startTimer: QTimer can only be used with threads started with QThread.

kuzulis

do you have an QApplication instance?

HamiltonQ

Hi!

QApplication instance is in the main.cpp file, but I'm starting the Timer on client.cpp file, which contains the call to the UI

kuzulis

Then you can google by the "QTimer can only be used with threads started with QThread." pattern. ;)

HamiltonQ

For three days I am trying to solve this. I have seen numerous topics, but none of them do what I want to do, which is to use the QTimer in the class that contains the UI. The example that the documentation give is for NON-GUI application. But I wanna exactly this

SGaist

Then let's first get back to the basics.

Do you still see this message if you create a default Qt Widget application and add

@
mainwindow.h

class MainWindow: public QWidget
{
// default code

public slots:
void testTimer();
}

mainwindow.cpp

MainWindow:MainWindow(QWidget *parent)
: QWidget(parent)
{
QTimer *timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), SLOT(testTimer()));

timer->start(20);
}

void MainWindow::testTimer()
{
qDebug() << "Timed out !";
}
@

to the default code ?

HamiltonQ

Hi, Samuel!

This works, I tested. But my base class is QMainWindow. I tried to change the base class for QWiget but it happened several errors.

Thanks, man!

SGaist

Just keep your QMainWindow based class, the only thing that was important was the part related to the QTimer

HamiltonQ

I have to change the base class to use QTimer?

JKSH

Can you show us your code for doWork()?

Note that in newer versions of Qt, the actual message is "QObject::startTimer: Timers can only be used with threads started with QThread". ("Timers", not "QTimer"!)

All QObjects have built-in timers. I don't think the message came from your QTimer, but rather from your QSerialPort.

SGaist

No you don't, QMainWindow is a QWidget as well

HamiltonQ

[quote author="JKSH" date="1422056561"]Can you show us your code for doWork()?

Note that in newer versions of Qt, the actual message is "QObject::startTimer: Timers can only be used with threads started with QThread". ("Timers", not "QTimer"!)

All QObjects have built-in timers. I don't the message came from your QTimer, but rather from your QSerialPort.[/quote]

@void client::readFlightData(){

//QMessageBox::information(this,"", "txtReadFlightData");

serial->write("gFD;");

if (serial->waitForBytesWritten(timeout))
{

    if(serial->waitForReadyRead(timeout))
    {
        txtReadFlightData = serial->readAll();
        listReadFlightData = txtReadFlightData.split(";", QString::SkipEmptyParts);

        if(listReadFlightData.size()==7)
        {
            if(ui->SelectUnitsAmerican->isChecked()==1) // Unidades no SI
            {

                ui->txtPitch->setText(listReadFlightData[0]);
                ui->txtRoll->setText(listReadFlightData[1]);
                ui->txtHeightGPS->setText(QString::number(listReadFlightData[2].toDouble()));
                ui->txtHeightBarometer->setText(QString::number(listReadFlightData[3].toDouble()));
                ui->txtSpeedPitot->setText(QString::number(listReadFlightData[4].toDouble()));
                ui->txtSpeedGPS->setText(QString::number(listReadFlightData[5].toDouble()));
                ui->txtVerticalSpeed->setText(QString::number(listReadFlightData[6].toDouble()));

                countLostSerial = 0;
                listReadFlightData.clear();

            }else{ // U.S. Customary

                ui->txtPitch->setText(listReadFlightData[0]);
                ui->txtRoll->setText(listReadFlightData[1]);
                ui->txtHeightGPS->setText(QString::number(listReadFlightData[2].toDouble()*3.28084)); // Feet
                ui->txtHeightBarometer->setText(QString::number(listReadFlightData[3].toDouble()*3.28084)); // Feet
                ui->txtSpeedPitot->setText(QString::number(listReadFlightData[4].toDouble()*2.2369)); // Miles per hour
                ui->txtSpeedGPS->setText(QString::number(listReadFlightData[5].toDouble()*2.2369)); // Miles per hour
                ui->txtVerticalSpeed->setText(QString::number(listReadFlightData[6].toDouble()*2.2369)); // Miles per hour
                countLostSerial = 0;
                listReadFlightData.clear();

            }

        }else
            countLostSerial += 1;

    }

}

if(countLostSerial == 250){
    countLostSerial = 0;
    disconnectSerial();

}

}@

HamiltonQ

[quote author="JKSH" date="1422056561"]Can you show us your code for doWork()?

Note that in newer versions of Qt, the actual message is "QObject::startTimer: Timers can only be used with threads started with QThread". ("Timers", not "QTimer"!)

All QObjects have built-in timers. I don't the message came from your QTimer, but rather from your QSerialPort.[/quote]

Hey man, thanks for the help!

I think that's the problem. I did it:

@QThread * thread = new QThread ();
QSerialPort * = new serial QSerialPort ();
Serial-> moveToThread (thread);@

But nothing has changed. I keep getting:

@QObject :: startTimer: QTimer can only be used with threads started with QThread.@

Can you tell me what should I do? I searched for some topics but nothing they say solved the problem. Thanks a lot!!

SGaist

[quote author="HamiltonQ" date="1422400475"]
@QThread * thread = new QThread ();
QSerialPort * = new serial QSerialPort ();
Serial-> moveToThread (thread);@
[/quote]

Did you mean:

@
QThread * thread = new QThread ();
QSerialPort *serial = new QSerialPort ();
serial-> moveToThread (thread);
@
?

HamiltonQ

[quote author="SGaist" date="1422405461"][quote author="HamiltonQ" date="1422400475"]
@QThread * thread = new QThread ();
QSerialPort * = new serial QSerialPort ();
Serial-> moveToThread (thread);@
[/quote]

Did you mean:

@
QThread * thread = new QThread ();
QSerialPort *serial = new QSerialPort ();
serial-> moveToThread (thread);
@
?[/quote]

Hi SGaist!

Yes. I ended up writing wrong. I did it but did not work. Do you have any suggestion? Thaks!

SGaist

Just to be sure I'm understanding your code correctly: you are moving your QSerialPort instance to a thread and then using the blocking functions in your widget code ?