Need help passing data to qml

[brasscs]

Hi i am having difficulty in passing a struct from cpp to qml. Can someone give me some pointers. I am using qt 5.4/64 bit under debian lenny rc1. Here is what i have been working with which was just a new dialog project with the following added. Note the code seems to work if i pass it just a string but not with a simple struct.

my .h

namespace Ui {
class Dialog;
struct MyStruct {
    int i;
    QString name;
};
}
 
Q_DECLARE_METATYPE(Ui::MyStruct)
#endif // DIALOG_H

namespace Ui {
class Dialog;
struct MyStruct {
    int i;
    QString name;
};
}

Q_DECLARE_METATYPE(Ui::MyStruct)
#endif // DIALOG_H

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.cpp file

Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog)
{
    ui->setupUi(this);
    test();
}
 
void Dialog::test() {
    using namespace Ui;
    MyStruct test;
 
    test.i=12;
    test.name="Hello world";
 
    QVariant v = QVariant::fromValue(test);
    QQmlEngine engine;
    QQmlComponent component(&engine, "/home/user/projects-qt5/test_qml/MyItem.qml");
    QObject *object = component.create();
 
    QVariant returnedValue;
    QVariant msg = "Hello from C++";
    QMetaObject::invokeMethod(object, "myQmlFunction",
                              Q_RETURN_ARG(QVariant, returnedValue),
                              Q_ARG(QVariant,v));
 
    qDebug() << "QML function returned:" << returnedValue.toString();
    qDebug() << "comp error is " << component.errors();
    delete object;
 
}

Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog)
{
    ui->setupUi(this);
    test();
}

void Dialog::test() {
    using namespace Ui;
    MyStruct test;

    test.i=12;
    test.name="Hello world";

    QVariant v = QVariant::fromValue(test);
    QQmlEngine engine;
    QQmlComponent component(&engine, "/home/user/projects-qt5/test_qml/MyItem.qml");
    QObject *object = component.create();

    QVariant returnedValue;
    QVariant msg = "Hello from C++";
    QMetaObject::invokeMethod(object, "myQmlFunction",
                              Q_RETURN_ARG(QVariant, returnedValue),
                              Q_ARG(QVariant,v));

    qDebug() << "QML function returned:" << returnedValue.toString();
    qDebug() << "comp error is " << component.errors();
    delete object;

}

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.qml

import QtQuick 2.0
 
// MyItem.qml
 
Item {
    function myQmlFunction(v) {
        console.log("Got message:",v.name)
        return "some return value"
    }
}

import QtQuick 2.0

// MyItem.qml

Item {
    function myQmlFunction(v) {
        console.log("Got message:",v.name)
        return "some return value"
    }
}

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[wysota]

It doesn't work like that. Wrapping a structure into a variant will not teach Qt to understand its structure and thus be able to access its members. For that you should derive your class from QObject and make members into properties or you should use QVariantMap and manually copy each field value to the map.

[anda_skoa]

Note the code seems to work if i pass it just a string but not with a simple struct.

You can pass any type that is wrapable in a QVariant.

If you mean that you can't access the data inside the variant, then see wysota's comment.

Cheers,
_

[brasscs]

ok so how about an example of passing a struct. gave up finding something online

[wysota]

ok so how about an example of passing a struct. gave up finding something online

MyStruct s;
QVariantMap map;
map["i"] = s.i;
map["name"] = s.name;
QVariant v = map;
QMetaObject::invokeMethod(object, "myQmlFunction",
                              Q_RETURN_ARG(QVariant, returnedValue),
                              Q_ARG(QVariant,v));

MyStruct s;
QVariantMap map;
map["i"] = s.i;
map["name"] = s.name;
QVariant v = map;
QMetaObject::invokeMethod(object, "myQmlFunction",
                              Q_RETURN_ARG(QVariant, returnedValue),
                              Q_ARG(QVariant,v));

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[brasscs]

hey thanks for the code but it still does not work. this is what i am using

.cpp

using namespace Ui;
    QQmlEngine engine;
    QQmlComponent component(&engine, "/home/user/projects-qt5/test_qml/MyItem.qml");
    QObject *object = component.create();
    QVariant returnedValue;
 
    MyStruct s;
    s.i=12;
    s.name="Hello QML";
    QVariantMap map;
    map["i"] = s.i;
    map["name"] = s.name;
 
    QVariant v = map;
    QMetaObject::invokeMethod(object, "myQmlFunction",
                                  Q_RETURN_ARG(QVariant, returnedValue),
                                  Q_ARG(QVariant,v));

using namespace Ui;
    QQmlEngine engine;
    QQmlComponent component(&engine, "/home/user/projects-qt5/test_qml/MyItem.qml");
    QObject *object = component.create();
    QVariant returnedValue;

    MyStruct s;
    s.i=12;
    s.name="Hello QML";
    QVariantMap map;
    map["i"] = s.i;
    map["name"] = s.name;

    QVariant v = map;
    QMetaObject::invokeMethod(object, "myQmlFunction",
                                  Q_RETURN_ARG(QVariant, returnedValue),
                                  Q_ARG(QVariant,v));

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.h

namespace Ui {
class Dialog;
struct MyStruct {
    int i;
    QString name;
};
}
...
Q_DECLARE_METATYPE(Ui::MyStruct)
#endif // DIALOG_H

namespace Ui {
class Dialog;
struct MyStruct {
    int i;
    QString name;
};
}
...
Q_DECLARE_METATYPE(Ui::MyStruct)
#endif // DIALOG_H

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.qml

import QtQuick 2.0
 
// MyItem.qml
 
Item {
 
    function myQmlFunction(v) {
        console.log("Got message:",v.name)
        return "some return value"
    }
}

import QtQuick 2.0

// MyItem.qml

Item {

    function myQmlFunction(v) {
        console.log("Got message:",v.name)
        return "some return value"
    }
}

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app output
qml: QML Got message: undefined
QML function returned: "some return value"
comp error is ()

[wysota]

It works just fine for me.

#include <QtGui>
#include <QtQml>
 
int main(int argc, char **argv) {
  QGuiApplication app(argc, argv);
  QQmlEngine e;
  QQmlComponent c(&e, "test.qml");
  QObject *o = c.create();
  QVariantMap m;
  m["i"] = 10;
  m["name"] = "someName";
  QVariant v = m;
  QVariant ret;
  QMetaObject::invokeMethod(o, "testFunc", Q_RETURN_ARG(QVariant, ret), Q_ARG(QVariant, v));
//  return app.exec();
  return 0;
}

#include <QtGui>
#include <QtQml>

int main(int argc, char **argv) {
  QGuiApplication app(argc, argv);
  QQmlEngine e;
  QQmlComponent c(&e, "test.qml");
  QObject *o = c.create();
  QVariantMap m;
  m["i"] = 10;
  m["name"] = "someName";
  QVariant v = m;
  QVariant ret;
  QMetaObject::invokeMethod(o, "testFunc", Q_RETURN_ARG(QVariant, ret), Q_ARG(QVariant, v));
//  return app.exec();
  return 0;
}

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import QtQml 2.0
 
QtObject {
  function testFunc(v) { console.log("v.name = ", v.name); }
}

import QtQml 2.0

QtObject {
  function testFunc(v) { console.log("v.name = ", v.name); }
}

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[brasscs]

hey wysota

i finally found my error. the code you supplied is now working fine.

thanks for your help.