QCustomPlot QML

[Dooham]

Hello,
I was trying to integrate a qml program that can represent math expressions. I saw that there were a library for that goal called QCustomPlot and I also saw a example of how can I integrate it with QML: https://www.qcustomplot.com/index.php/support/forum/172

However when I run the code I have the following error:
QWidget: Cannot create a QWidget without QApplication

This is my code:

.pro

QT += quick
CONFIG += c++11
QT += script
QT += printsupport
QT += widgets
# The following define makes your compiler emit warnings if you use
# any Qt feature that has been marked deprecated (the exact warnings
# depend on your compiler). Refer to the documentation for the
# deprecated API to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES += \
        calculadorafunciones.cpp \
        customplotitem.cpp \
        main.cpp \
        qcustomplot.cpp

RESOURCES += qml.qrc

# Additional import path used to resolve QML modules in Qt Creator's code model
QML_IMPORT_PATH =

# Additional import path used to resolve QML modules just for Qt Quick Designer
QML_DESIGNER_IMPORT_PATH =

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

HEADERS += \
    calculadorafunciones.h \
    customplotitem.h \
    qcustomplot.h

main.cpp (There are two comments for two librery because I tried with different options but any of them worked)

//#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "exprtk/exprtk.hpp"
#include <QQmlContext>
#include "calculadorafunciones.h"
#include "customplotitem.h"
#include <QtWidgets/QApplication>
//#include <QApplication>
int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;

    qmlRegisterType<CalculadoraFunciones>("mi.calculadora", 1, 0,"MyCalculadora");
    qmlRegisterType<CustomPlotItem>("CustomPlot", 1, 0, "CustomPlotItem");

    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}

customplotitem.h

#pragma once

#include <QtQuick>
#include "qcustomplot.h"
class QCustomPlot;

class CustomPlotItem : public QQuickPaintedItem
{
    Q_OBJECT

public:
    CustomPlotItem( QQuickItem* parent = 0 );
    virtual ~CustomPlotItem();

    void paint( QPainter* painter );

    Q_INVOKABLE void initCustomPlot();

protected:
    void routeMouseEvents( QMouseEvent* event );

    virtual void mousePressEvent( QMouseEvent* event );
    virtual void mouseReleaseEvent( QMouseEvent* event );
    virtual void mouseMoveEvent( QMouseEvent* event );
    virtual void mouseDoubleClickEvent( QMouseEvent* event );

    void setupQuadraticDemo( QCustomPlot* customPlot );

private:
    QCustomPlot*         m_CustomPlot;

private slots:
    void graphClicked( QCPAbstractPlottable* plottable );
    void onCustomReplot();
    void updateCustomPlotSize();

};

customplotitem.cpp

#include "CustomPlotItem.h"

#include <QDebug>

CustomPlotItem::CustomPlotItem( QQuickItem* parent ) : QQuickPaintedItem( parent )
    , m_CustomPlot( nullptr )
{
    setFlag( QQuickItem::ItemHasContents, true );
    // setRenderTarget(QQuickPaintedItem::FramebufferObject);
    // setAcceptHoverEvents(true);
    setAcceptedMouseButtons( Qt::AllButtons );

    connect( this, &QQuickPaintedItem::widthChanged, this, &CustomPlotItem::updateCustomPlotSize );
    connect( this, &QQuickPaintedItem::heightChanged, this, &CustomPlotItem::updateCustomPlotSize );
}

CustomPlotItem::~CustomPlotItem()
{
    delete m_CustomPlot;
    m_CustomPlot = nullptr;
}

void CustomPlotItem::initCustomPlot()
{
    m_CustomPlot = new QCustomPlot();

    updateCustomPlotSize();

    setupQuadraticDemo( m_CustomPlot );

    connect( m_CustomPlot, &QCustomPlot::afterReplot, this, &CustomPlotItem::onCustomReplot );

    m_CustomPlot->replot();
}


void CustomPlotItem::paint( QPainter* painter )
{
    if (m_CustomPlot)
    {
        QPixmap    picture( boundingRect().size().toSize() );
        QCPPainter qcpPainter( &picture );

        //m_CustomPlot->replot();
        m_CustomPlot->toPainter( &qcpPainter );

        painter->drawPixmap( QPoint(), picture );
    }
}

void CustomPlotItem::mousePressEvent( QMouseEvent* event )
{
    qDebug() << Q_FUNC_INFO;
    routeMouseEvents( event );
}

void CustomPlotItem::mouseReleaseEvent( QMouseEvent* event )
{
    qDebug() << Q_FUNC_INFO;
    routeMouseEvents( event );
}

void CustomPlotItem::mouseMoveEvent( QMouseEvent* event )
{
    routeMouseEvents( event );
}

void CustomPlotItem::mouseDoubleClickEvent( QMouseEvent* event )
{
    qDebug() << Q_FUNC_INFO;
    routeMouseEvents( event );
}

void CustomPlotItem::graphClicked( QCPAbstractPlottable* plottable )
{
    qDebug() << Q_FUNC_INFO << QString( "Clicked on graph '%1 " ).arg( plottable->name() );
}

void CustomPlotItem::routeMouseEvents( QMouseEvent* event )
{
    if (m_CustomPlot)
    {
        QMouseEvent* newEvent = new QMouseEvent( event->type(), event->localPos(), event->button(), event->buttons(), event->modifiers() );
        //QCoreApplication::sendEvent( m_CustomPlot, newEvent );
        QCoreApplication::postEvent( m_CustomPlot, newEvent );
    }
}

void CustomPlotItem::updateCustomPlotSize()
{
    if (m_CustomPlot)
    {
        m_CustomPlot->setGeometry( 0, 0, width(), height() );
    }
}

void CustomPlotItem::onCustomReplot()
{
    qDebug() << Q_FUNC_INFO;
    update();
}

void CustomPlotItem::setupQuadraticDemo( QCustomPlot* customPlot )
{
    // make top right axes clones of bottom left axes:
    QCPAxisRect* axisRect = customPlot->axisRect();

    // generate some data:
    QVector<double> x( 101 ), y( 101 );   // initialize with entries 0..100
    QVector<double> lx( 101 ), ly( 101 ); // initialize with entries 0..100
    for (int i = 0; i < 101; ++i)
    {
        x[i] = i / 50.0 - 1;              // x goes from -1 to 1
        y[i] = x[i] * x[i];               // let's plot a quadratic function

        lx[i] = i / 50.0 - 1;             //
        ly[i] = lx[i];                    // linear
    }
    // create graph and assign data to it:
    customPlot->addGraph();
    customPlot->graph( 0 )->setPen( QPen( Qt::red ) );

    customPlot->graph( 0 )->setData( x, y );

    customPlot->addGraph();
    customPlot->graph( 1 )->setPen( QPen( Qt::magenta ) );

    customPlot->graph( 1 )->setData( lx, ly );

    // give the axes some labels:
    customPlot->xAxis->setLabel( "x" );
    customPlot->yAxis->setLabel( "y" );
    // set axes ranges, so we see all data:
    customPlot->xAxis->setRange( -1, 1 );
    customPlot->yAxis->setRange( -1, 1 );

    customPlot ->setInteractions( QCP::iRangeDrag | QCP::iRangeZoom | QCP::iSelectPlottables );
    connect( customPlot, SIGNAL( plottableClick( QCPAbstractPlottable*, QMouseEvent* ) ), this, SLOT( graphClicked( QCPAbstractPlottable* ) ) );

Does anyone know what is wrong?
Thanks for the help

[jsulm]

@Dooham said in QCustomPlot QML:

QWidget: Cannot create a QWidget without QApplication

Do you have any static QWidget derived instances in your app somewhere?
Also, did you try with QApplication instead of QGuiApplication?
From https://doc.qt.io/qt-5/qguiapplication.html
"For QWidget based Qt applications, use QApplication instead, as it provides some functionality needed for creating QWidget instances."

[Dooham]

@jsulm In my Qml file I have some buttons and a textField. This is the file qml:

import QtQuick 2.12
import QtQuick.Controls 2.5
import mi.calculadora 1.0
import CustomPlot 1.0

ApplicationWindow {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")
    MyCalculadora{
        id: miCalculadora
    }
    Row{
        Button{
            text: "Raiz"
            onClicked: {
                inputExpresion.text= inputExpresion.text+" sqrt("

            }
        }
        Button{
            text: "Logaritmo"
            onClicked: {
                inputExpresion.text= inputExpresion.text+" log("

            }
        }
        Button{
            text: "Coseno"
            onClicked: {
                inputExpresion.text= inputExpresion.text+" cos("

            }
        }
        Button{
            text: "Seno"
            onClicked: {
                inputExpresion.text= inputExpresion.text+" sin("

            }
        }
        Button{
            text: "Tangente"
            onClicked: {
                inputExpresion.text= inputExpresion.text+" tan("

            }
        }
        Button{
            text: "Limpiar"
            onClicked: {
                inputExpresion.text= ""

            }
        }
    }
    Column{
        anchors.centerIn: parent

        TextField{
            id: inputExpresion
            width:150
            text: ""
            focus: true
            selectByMouse: true
            inputMethodHints: Qt.ImhDigitsOnly
            //validator: DoubleValidator{notation: DoubleValidator.StandardNotation}

            //onEditingFinished: {cuadriculaItem.parametrosCuad[1]=Funciones.deStringADouble(inputParam1.text)}


        }


        Button{
            id: miBoton
            text: "Pulsar Aqui"
            onClicked: {
                miCalculadora.evaluarFuncion(inputExpresion.text)
            }
        }

        CustomPlotItem{
        id:plot
        height: 100
        width: 100
        Component.onCompleted: plot.initCustomPlot();
        }
    }
}

Yes, I tried with QApplication instead of QGuiApplication.

[jsulm]

@Dooham What about stativ QWidget instances?

[Dooham]

@jsulm I think I dont have any of them.

[Dooham]

@jsulm ok I found out the solution. I had to change the engine for a QQuickView in the main.cpp. But is there any method to create a new kind if widget un qml and insert It like I can maje with a button ?