problem with getting data from c++ to qml using QtQuickWidget

dziko147

Hello ,
Currently I displayed data from c++ to Qml QQuickwidget using signal and slots .
I used this connection :
QObject::connect(rootObject, SIGNAL(qmlVoltage()),
this, SLOT(onSwitchVoltageClicked()),Qt::QueuedConnection);

first problem: I would like to change this data from another Qdialog , when i change data there is no update in my qmlfile .

Also I tried to display different qml file in the same Qquickwidget using signal and slots .
Second problem: when i display the second qml file i get this error :

TypeError: Cannot read property 'Voltage' of null .

I will appreciate any suggestion .
thank you

mzimmers

@dziko147 there are a few steps involved in getting C++ data to your QML. Here's a good start to understanding this.

Since you didn't post any code, we can't tell how much of this setup work you've done.

JKSH

Hi @mzimmers, your link is missing; could you please edit it in?

dziko147

@mzimmers thanks for your reply :)
Currently i use this code :

#ifndef BACKEND_H
#define BACKEND_H

#include <QObject>
#include <QQmlEngine>

class Backend : public QObject
{
Q_OBJECT
Q_PROPERTY(QString directiontext READ getdirectiontext WRITE setdirectiontext NOTIFY directiontextChanged)
QML_ELEMENT

public:
explicit Backend(QObject *parent = nullptr);
QString getdirectiontext() {return m_directiontext;}
;}

//Setter methode //

void setdirectiontext(QString text);

signals:
void directiontextChanged();

private :
QString m_directiontext;

};

#endif // BACKEND_H

//Backend.cpp
#include"backend.h"
#include<QDebug>
Backend::Backend(QObject *parent ) :QObject(parent)
{
m_directiontext="test direct";

void Backend::setdirectiontext(QString text)
{
qDebug("signal direction called");
if(m_directiontext == text)
return;
m_directiontext = text;
emit directiontextChanged();
}

//MainWindow
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
m_ui(new Ui::MainWindow),

{

Backend back ;
m_ui->quickWidget->rootContext()->setContextProperty("cppObject",&back);

//In my Qml file :
text: qsTr(cppObject.directiontext)

//then i would like to change the data by :
Backend back;
QString Mode= ui->modecommande->currentText();
qDebug() << Mode << "this is Mode select commande" ;
back.setdirectiontext(Mode);

I hope that my question is clear :)

jsulm

@dziko147 Please format your code properly, it makes it easier for others to read and understand it.

dziko147

#ifndef BACKEND_H
#define BACKEND_H

#include <QObject>
#include <QQmlEngine>

class Backend : public QObject
{
Q_OBJECT
Q_PROPERTY(QString directiontext READ getdirectiontext WRITE setdirectiontext NOTIFY directiontextChanged)
QML_ELEMENT

public:
explicit Backend(QObject *parent = nullptr);
QString getdirectiontext() {return m_directiontext;}
;}

}
//Setter methode //

void setdirectiontext(QString text);
signals:
void directiontextChanged();

private :
QString m_directiontext;

};

#endif // BACKEND_H

//Backend.cpp
#include"backend.h"
#include<QDebug>
Backend::Backend(QObject *parent ) :QObject(parent)
{
m_directiontext="test direct";

void Backend::setdirectiontext(QString text)
{
qDebug("signal direction called");
if(m_directiontext == text)
return;
m_directiontext = text;
emit directiontextChanged();
}

//MainWindow
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
m_ui(new Ui::MainWindow),

{

Backend back ;
m_ui->quickWidget->rootContext()->setContextProperty("cppObject",&back);

//In my Qml file :
text: qsTr(cppObject.directiontext)

//then i would like to change the data by :
Backend back;
QString Mode= ui->modecommande->currentText();
qDebug() << Mode << "this is Mode select commande" ;
back.setdirectiontext(Mode);