Error when using object of QChart type

[Duc Nguyen]

• I'm having trouble when using object of QChart type. I want to append points to the chart and make it scrollable but there appears to be some errors in cpp file.

#include "myserialport.h"
#include <QSerialPortInfo>
#include <QDebug>
//#include <QTimer>
#include <QTime>
#include <QDateTime>
#include <math.h>
#include <QtCharts/QValueAxis>
#include <QLine>
#include <QtCharts/QChart>

QT_USE_NAMESPACE
int count=0;
MySerialPort::MySerialPort(QObject *parent) : QObject(parent),m_series(0)
{
    myPort=new QSerialPort;
    serialBuffer = "";
    parsed_data = "";
    temperature_value = 0.0;
    //m_series=0;
}

MySerialPort::~MySerialPort()
{
    delete myPort;
}
double MySerialPort::readData_slot()
{
    QByteArray buff;

    QStringList buffer_split = serialBuffer.split(","); //  split the serialBuffer string, parsing with ',' as the separator
    if(buffer_split.length() < 3){
        buff=myPort->readAll();
        serialBuffer = serialBuffer + QString::fromStdString(buff.toStdString());
        buff.clear();
    }
    else{
        // the second element of buffer_split is parsed correctly, update the temperature value on temp_lcdNumber
        serialBuffer = "";
        //qDebug() << buffer_split<< "\n";
        parsed_data = buffer_split[1];
        //temperature_value = (9/5.0) * (parsed_data.toDouble()) + 32; // convert to fahrenheit
        temperature_value = parsed_data.toDouble(); // celsius
        qDebug() << "Temperature: " << temperature_value << "\n";

        emit receiveData(temperature_value);
    }
    return temperature_value;
}
void MySerialPort::plot_chart(double x, double y)
{
    m_series->append(x,y);  //******ERROR*****
    // need to add scroll here
    QChart chart;   //******ERROR*****
    chart.scroll(x,y);  //******ERROR*****
}

• This is my qml file

import QtQuick 2.0
import QtQuick.Layouts 1.12
import QtQuick.Controls 2.5
import QtCharts 2.15
Item {
    id:root
    signal sendSettingInfoSignal(int state)
    signal sendDataSignal(string data)
    property double rmsec:0

        Rectangle{ //create border
            Layout.fillWidth: true
            Layout.fillHeight: true
            Layout.columnSpan:2
            border.width: 1
            border.color: "gray"
            height: 4

            //display chart in the screen
            ChartView {
                id: chart
                anchors.fill:parent
                antialiasing: true
                animationOptions: ChartView.AllAnimations
                LineSeries {
                    id: line
                    name: "Realtime data chart"
                    axisY: ValuesAxis{
                        min: 0.0
                        max: 40.0
                        tickCount: 6
                    }
//                    axisX: DateTimeAxis{
//                        tickCount: 5
//                        format: "hh:mm:ss"
////                        max: new Date(2022,5,6,9,49,00)
////                        min: new Date(2022,5,6,9,48,00)
//                    }
                    axisX: ValuesAxis{
                        min: 0.0
                        max: 20.0
                    }
                }

            }

        }
        //update time with data
        Timer{
            id: refreshTimer
            interval: 500
            running: true
            repeat: true
            onTriggered: {
                rmsec++;
                if(cpp_obj.readIsMyPortOpen()){
                //line.append(rmsec,cpp_obj.readData_slot());
                   cpp_obj.plot_chart(rmsec,cpp_obj.readData_slot());
                }
            }
        }
}

• These are my errors:
  

[jsulm]

@Duc-Nguyen Did you add

QT += charts

to your pro file as shown in https://doc.qt.io/qt-5/qtcharts-index.html ?

[Duc Nguyen]

Thanks for your reply. That's what I forgot to do :(

[Duc Nguyen]

@jsulm after I added that to my pro file and run the code, an error message appeared:

[jsulm]

@Duc-Nguyen Please use the debugger to get the stack trace after crash

[Duc Nguyen]

@jsulm My screen showed this when I started debugger:

[jsulm]

@Duc-Nguyen

1. Is m_series a valid pointer?
2. Why do you create chart as local variable? You know that it will be deleted as soon as plot_chart() finishes?