QDateTimeAxis always shows 1970

[pauledd]

Hi there

I try to draw a chart with a QDateTimeAxis but it gets always filled with the default date 01.01.1970. I read the dates and the values by a function (updateValues) from an csv file into a struct that fills then a QList of the same struct type.
Thats a sample line of the csv:

2017-03-11 07:50:01,17.7,1026.2,2.9,99.9

mainwindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QList>
#include <QtCharts>
using namespace QtCharts;

struct Wstruct{
	QDateTime date;
	double press;
};

class MainWindow:public QMainWindow
{
	Q_OBJECT
public:
	explicit MainWindow(QWidget *parent = 0);
	~MainWindow();
private:
	QLineSeries *seriesPressure;
	QChart *chart;
	QDateTimeAxis *axisX;
	QValueAxis *axisY;
	QChartView *chartView;
	QList<Wstruct> values;
	Wstruct filler;
	QWidget *widgetChart;
private slots:
	void updateValues();
};

#endif // MAINWINDOW_H

mainwindow.cpp:

#include "mainwindow.h"
#include <QFile>
#include <QDebug>
#include <QTime>
using namespace QtCharts;

MainWindow::MainWindow(QWidget *parent) :
	QMainWindow(parent)
{
	this->setFixedSize(800,480);
	
	seriesPressure = new QLineSeries();
	chart = new QChart();
	chart->legend()->hide();
	chart->addSeries(seriesPressure);
	axisX = new QDateTimeAxis;
	axisX->setFormat("hh:mm dd.MM.yyyy");
	chart->addAxis(axisX,Qt::AlignBottom);
	axisY = new QValueAxis;
	chart->addAxis(axisY,Qt::AlignRight);
	seriesPressure->attachAxis(axisX);
	seriesPressure->attachAxis(axisY);
	chartView = new QChartView(chart);
	
	widgetChart = new QWidget(this);
	widgetChart->setGeometry(15,15,760,320);
	QGridLayout *gl = new QGridLayout(widgetChart);
	gl->addWidget(chartView);
	updateValues();
}

MainWindow::~MainWindow()
{
}

void MainWindow::updateValues()
{
	QFile file("289_24h.log");
	if (!file.open(QIODevice::ReadOnly)) {
		qDebug() << file.errorString();
	}
         // clear previous updates
	seriesPressure->clear();
	values.clear();
	
	while (!file.atEnd()) {
		QByteArray line = file.readLine();
		filler.date = QDateTime::fromString(line.split(',').at(0),"yyyy-MM-dd hh:mm:ss");
		filler.press = line.split(',').at(2).toDouble();
		values.append(filler);
	} 
	
	for (int i=0; i<values.size();i++)
	{
		seriesPressure->append(values.at(i).date.toMSecsSinceEpoch(),values.at(i).press);	
		qDebug()<<values.at(i).date.toMSecsSinceEpoch()<<values.at(i).press;
	}
}

After I append the values to the list I did a qDebug to see if the values for the date and the y values are correctly stored in the list but it seems the are proper stored. But why does the QDateTimeAxis always plot 1970?
Any idea anyone?

[J.Hilk]

@pauledd

hi,

I believe 1970 is the default time.
Therefore I think

QDateTime::fromString(line.split(',').at(0),"yyyy-MM-dd hh:mm:ss")

results in an invalid QDateTime -> 1970. Can you check if that conversion from String to QdateTime results in a valid and correct date?

[pauledd]

yes it seems, the line:

		qDebug()<<values.at(i).date.toMSecsSinceEpoch()<<values.at(i).press;

outputs this:

...
1489215301000 1026.1
1489215601000 1026.1
...

and thats msecsSinceEpoch that QDateTimeAxis expects.

[pauledd]

ok I think I solved it. It was all correct, the data was in the chart and the conversion was valid but it simply displayed the wrong range. I believe thats because if you explicitly specify an Axis instead of creating createDefaultAxes() you have to specify the range manually with axisX->setMin or axisX->setRange, like in my case for the QDateTimeAxis. I had to:

axisX->setMin(values.first().date);
axisX->setMax(values.last().date);

to get the proper range to display.