using QTimer

[Dean21]

So I am using MQTT and want to use a timer to wait a set amount of time before doing something, I have used this method in different functions in my code that come after the widget destructor. But when I use this method as shown in the code below I get a debug message saying
"Timers can only be used with threads started with QThread"

Ihave tried a couple other methods but couldnt get it to work, and I need it to be a timer not a delay as I want the rest of the program to function while waiting.

#include "widget.h"
#include "./ui_widget.h"
#include <QPalette>
#include <QDebug>
#include <QTimer>
#include <QString>


#include <string>
#include <cstring>
#include <iostream>
#include <time.h>
#include </home/dave/mosquitto/include/mosquitto.h> //needed for mosquitto MQTT

#include <QApplication>
//-----for qt qrapper for mosquitto-----
#include <QCoreApplication>
#include <QTime>
#include "QMMqttClient.h"
//--------------------------------------

#include <QThread>


//------------IP Adresses------------
char RPi_IP[] = "xxxxxxx";
char Linux_PC_IP[] = "xxxxxxxx";
//-----------------------------------


Widget::Widget(QWidget *parent): QWidget(parent)
    , ui(new Ui::Widget)


{
    ui->setupUi(this);


        /* An example of unsecure connection */
        client.initialize("12", RPi_IP, 1883); //initialise connection with ID 12, R_Pi IP, and port 1883

        client.connect(); // connect with above parameters

        client.publishMesage("Closed", "0");



        //----------------------function to connect to the raspberry pi----------------------
                QObject::connect(&client, &QMMqttClient::onConnected, this ,[this](){
                    qDebug() << " QMMqttClient::onConnected handler, subscribe to topic...";
                    client.subscribeTopic("Temp Alarm");
                });
        //-----------------------------------------------------------------------------------


        QObject::connect(&client, &QMMqttClient::onMessageReceived, [this](const QString &topic, const QByteArray &msg) {


            ui->Alarm_Triggered_Label->setText("Temperature alarm of PSU triggered, HV output disabled for 5 minutes");

            ui->HV_ON_OFF_Button->setEnabled(false);


            QTimer::singleShot(3000, this, [this](){//publish after 3 seconds
                client.publishMesage("Alarm_5_min_cooldown_complete", "1");
            });


        });



}

Widget::~Widget()
{
    delete ui;
}

Any help would be great,
Thanks,
Dean

[Dean21]

@Dean21 I just figured this out myself and am just posting in case someone else has the same issue.

My function where I want the timer now looks like shown below:

        QObject::connect(&client, &QMMqttClient::onMessageReceived, [this](const QString &topic, const QByteArray &msg) {

            ui->Alarm_Triggered_Label->setText("Temperature alarm of PSU triggered, HV output disabled for 5 minutes");
            ui->HV_ON_OFF_Button->setEnabled(false);

            // Use QMetaObject::invokeMethod to execute the code in the main GUI thread
            QMetaObject::invokeMethod(this, "publishAfterDelay", Qt::QueuedConnection);

        });

And the call to function publishAfterDelay() looks like shown below:

void Widget::publishAfterDelay()
{
    QTimer::singleShot(3000, this, [this]() {
        client.publishMesage("Alarm_5_min_cooldown_complete", "1");
        qDebug() << "timer pinged";
    });
}

Hope this helps anyone else.

[luebleton]

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