CPP QML communication

[nestuser]

Now I'm working with QT Quick Project -> QT Quick application. I loaded a QML file using QDeclaratieveView and did the CPP to QML and QML to CPP communication. It is worked...

Can i do the same in any other QT applications like QT Widget-> QT GUI or Other Project??

[spirit]

For other GUI - yes. But, anyway, you need QDeclaratieveView instance.

[nestuser]

thanks for your replay.
But I opened a "QT Widget->QT GUI App" and try to include QDeclarativeView.
then i got the error QDeclarativeView: No such file or directory..

[spirit]

That's because you didn't add QT += declarative in your pro-file.

[nestuser]

yes, it is worked...
thank you very much.....

I used

qmlRegisterType<Widget>("File", 1,1, "TextUpdate");

qmlRegisterType<Widget>("File", 1,1, "TextUpdate");

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to register the class in main and in the QML file I imported the file and called the function

TextUpdate{
        id: sample1
    }

TextUpdate{
        id: sample1
    }

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. then i got the visual c++ runtime library error..

[spirit]

What's an error message?

[nestuser]

That error message says that "The application has requested the runtime to terminate it in an unusual way"

[spirit]

We can only guess what's wrong without seeing your code.

[nestuser]

ok. I will show you my code.

This is my Widget.h

#ifndef WIDGET_H
#define WIDGET_H
 
#include <QWidget>
 
namespace Ui {
class Widget;
}
 
class Widget : public QWidget
{
    Q_OBJECT
 
public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();
    void ShowQML();
     void setText(QString);
 
private:
    Ui::Widget *ui;
};
 
#endif // WIDGET_H

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT
    
public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();
    void ShowQML();
     void setText(QString);

private:
    Ui::Widget *ui;
};

#endif // WIDGET_H

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This is my Widget.cpp

#include "widget.h"
#include "ui_widget.h"
#include <QtGui>
#include <QDeclarativeComponent>
#include <QDeclarativeEngine>
#include <QDeclarativeItem>
#include <QDeclarativeView>
 
Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
 
    ui->setupUi(this);
    qDebug()<<"Inside cnstrctr";
}
void Widget::ShowQML()
{
    QDeclarativeView *testView = new QDeclarativeView();
    testView->setSource(QUrl::fromLocalFile("test2.qml"));
     testView->show();
}
 
Widget::~Widget()
{
    delete ui;
}
void Widget::setText(QString msg)
{
    qDebug()<<"Inside slot in CPP";
    //SendSignal();
 
}

#include "widget.h"
#include "ui_widget.h"
#include <QtGui>
#include <QDeclarativeComponent>
#include <QDeclarativeEngine>
#include <QDeclarativeItem>
#include <QDeclarativeView>

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{

    ui->setupUi(this);
    qDebug()<<"Inside cnstrctr";
}
void Widget::ShowQML()
{
    QDeclarativeView *testView = new QDeclarativeView();
    testView->setSource(QUrl::fromLocalFile("test2.qml"));
     testView->show();
}

Widget::~Widget()
{
    delete ui;
}
void Widget::setText(QString msg)
{
    qDebug()<<"Inside slot in CPP";
    //SendSignal();

}

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this is the main file

#include <QtGui/QApplication>
#include "widget.h"
#include <qdeclarative.h>
#include <QDeclarativeView>
#include <QApplication>
#include <QBoxLayout>
 
int main(int argc, char *argv[])
{
    qmlRegisterType<Widget>("File", 1,1, "TextUpdate");
    QApplication a(argc, argv);
    Widget w;
    //w.show();
    w.ShowQML();
    return a.exec();
}

#include <QtGui/QApplication>
#include "widget.h"
#include <qdeclarative.h>
#include <QDeclarativeView>
#include <QApplication>
#include <QBoxLayout>

int main(int argc, char *argv[])
{
    qmlRegisterType<Widget>("File", 1,1, "TextUpdate");
    QApplication a(argc, argv);
    Widget w;
    //w.show();
    w.ShowQML();
    return a.exec();
}

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and the QML file is

// import QtQuick 1.0 // to target S60 5th Edition or Maemo 5
import QtQuick 1.1
import File 1.1
 
Rectangle {
    width: 100
    height: 62
    TextUpdate{
        id: sample1
    }
}

// import QtQuick 1.0 // to target S60 5th Edition or Maemo 5
import QtQuick 1.1
import File 1.1

Rectangle {
    width: 100
    height: 62
    TextUpdate{
        id: sample1
    }
}

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[spirit]

First of all you have memory leak in Widget::ShowQML.
Second, are you trying to register Widget (which inherits QWidget) here qmlRegisterType<Widget>("File", 1,1, "TextUpdate");?

[nestuser]

Yes, Widget is my class name. I'm trying to register with that class name.

[spirit]

That's not possible. You can only register classes inherited from QObject. I know that QWidget inherits QObject, but you can't register widgets for using them in QML.

---

Added after 4 minutes:

QML relies heavily on Qt's meta object system and can only instantiate classes that derive from QObject. For visual element types, this will usually mean a subclass of QDeclarativeItem; for models used with the view elements, a subclass of QAbstractItemModel; and for arbitrary objects with properties, a direct subclass of QObject.

See Extending QML Functionalities using C++.

[nestuser]

yes, now it is worked...
one more doubt
In my project i have lots of CPP to QML communication. Then which UI is best for me, QT Quick or QT Widget?

[spirit]

It depends on what kind of UI do you what: modern fancy live ui (with animations and other stuff) or old school ui.

[nestuser]

I'm not developing QML file. I need only communication part.

[spirit]

So, you are working on the back-end. Then you should concentrate on architecting of the back-end structure. If you make the back-end independent from ui then you (or your colleagues) will be able to choose the best ui approach: QML or Qt widget-based.

[nestuser]

thank you very much..
I'm working on back-end. I need to emit only some signals to QML file.
I think QT widget is apt for it, right??

[spirit]

Yes, it is.