Get QtGraphs with XYModelMapper working

[Igor23]

Hallo,

I'm trying to get QtGraphs working with a model. But I only get a grey window:

The qml file:

import QtQuick
import QtGraphs
import graphsexample

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")
    GraphsView {
        antialiasing: true
        anchors.fill: parent
        //legend.visible: false
        LineSeries {
            XYModelMapper {
                model: Graphsmodel
                xSection: 0
                ySection: 1
            }
        }
    }
}

And the model cpp files:

#ifndef GRAPHSMODEL_H
#define GRAPHSMODEL_H

#include <cmath>
#include <QObject>
#include <QAbstractListModel>

#define PI 3.14159265359

class GraphsModel : public QAbstractTableModel
{
   Q_OBJECT

public:
    explicit GraphsModel();

    virtual int rowCount(const QModelIndex& parent = QModelIndex()) const;
    virtual int columnCount(const QModelIndex& parent = QModelIndex()) const;

    QVariant data(const QModelIndex &index, int role) const;
    virtual void populate();

protected:
    int ncoords;
    std::vector<double> xvalues;
    std::vector<double> yvalues;
    QList< std::pair<double,double> > mDatas;
};

#endif // GRAPHSMODEL_H

and

#include "graphsmodel.h"


GraphsModel::GraphsModel() : QAbstractTableModel()
{
    int icoords;
    ncoords= 100;
    xvalues= std::vector<double>(ncoords);
    yvalues= std::vector<double>(ncoords);

    for(icoords=0; icoords<ncoords; icoords++){
       xvalues[icoords]= double(5*icoords)*PI / 180.0;
       yvalues[icoords]= std::sin(xvalues[icoords]);
    }

    mDatas= QList< std::pair<double, double> >(ncoords);

    populate();

    return;
}

int GraphsModel::rowCount(const QModelIndex& parent) const
{
      return ncoords;
}

int GraphsModel::columnCount(const QModelIndex& parent) const
{
      return 2;
}

QVariant GraphsModel::data(const QModelIndex& index, int role) const
{
    int row = index.row();
    int column= index.column();

    if(row < 0 || row >= ncoords) {
        return 0;
    }

    if(column == 0) {
            return QVariant(std::get<0>(mDatas.at(row)));
    }
    else if(column == 1) {
            return QVariant(std::get<1>(mDatas.at(row)));
    }
    else return QVariant(0);
}


void GraphsModel::populate()
{
    int icoord;
    mDatas=QList< std::pair<double,double> >(ncoords);

    for(icoord=0; icoord<ncoords; icoord++){
        mDatas[icoord]= std::make_pair(xvalues[icoord], yvalues[icoord]);
    }

    emit dataChanged(index(0,0),index(ncoords-1,1));

    return;
}

The main.cpp file is:

#include <QGuiApplication>
#include <QQmlApplicationEngine>

#include "graphsmodel.h"

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    GraphsModel graphsmodel;
    qmlRegisterSingletonInstance("graphsexample", 1, 0, "Graphsmodel", &graphsmodel);

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/codeExampleQtGraphs/Main.qml")));

    return app.exec();
}

I hope anyone can help me. I think its only small error ...

[GrecKo]

You need to set the series property of your XYModelMapper.

[Igor23]

@GrecKo Thanks! I also found that out. But the lineseries must also have a color different from backround and there must be explicit axes. My working qml file is now:

import QtQuick
import QtGraphs
import graphsexample 1.0

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")
    GraphsView {
        id: graphsView
        antialiasing: true
        anchors.fill: parent
        //legend.visible: false
        ValueAxis {
            id: axisX
            min: 0
            max: 10  // Anpassen an Ihre Daten
            titleText: "X-Achse"
        }

        ValueAxis {
            id: axisY
            min: 0
            max: 10  // Anpassen an Ihre Daten
            titleText: "Y-Achse"
        }
        LineSeries {
            id: lineSeries
            color: "#00ff00"
            joinStyle: Qt.RoundJoin
            XYModelMapper {
                model: Graphsmodel
                series: lineSeries
                xSection: 0
                ySection: 1
            }
            axisX: axisX
            axisY: axisY
        }
    }
}

Also this Connections don't work. It must be Graphsmodel with captal letter in XYModelMapper:

    Connections{
        id: graphsmodel
        target: Graphsmodel
    }

[Igor23]

@GrecKo I have an additional question, because it is important for my project:
How can I update the axes in the following sense:

ValueAxis {
    id: axisX
    min: Graphsmodel.returnXmin()
    max: Graphsmodel.returnXmax()
    titleText: "X-Achse"
}

Even with fixed starting values this is not working for me.

[GrecKo]

Try to expose the xMin and xMan as properties with a NOTIFY signal instead to make the min and max binding automatically update. I guess it is currently calling returnXmin/max initially when the model is maybe empty, and then it isn't called again.

[Igor23]

@GrecKo How do you mean this exactly? Can you give an example code?

[Igor23]

And I have a second additional question: is there maximum number of points I can draw via Lineseries and XYModelMapper? It seems to me as there is a limit by Qt framework ...

[JoeCFD]

@Igor23 add the following in your model
Q_PROPERTY( float minX MEMBER m_fMinX NOTIFY minXChanged )
define m_fMinX and signal minXChanged in your model.

Do the same for maxX.

and

ValueAxis {
    id: axisX
    min: Graphsmodel.minX
    max: Graphsmodel.maxX
    titleText: "X-Achse"
}

[JoeCFD]

@Igor23 It seems there is no limit. But your drawing will get slower if there are too many points. You need some kind of optimization.

[SGaist]

The LineSeries type has a count property that returns the number of data points in the series so I would venture that the maximum int value is the limit but I wouldn't try to show that many data point anyway because it does not make sense. If anything, I would rather allow the user to zoom in/out of sections of a LineSeries if they need more precise data.