QML & Qt C++ : ReferenceError

[aymen_ka]

Hi,
I'm writing a QtQuick app, and I need to use some Qt C++ functions, but when I try to access to my class method I get this error: file:///C:/QtDev/test022-build-simulator-Simulator_Qt_for_MinGW_4_4__Qt_SDK__Debug/qml/test022/MainPage.qml:20: ReferenceError: Can't find variable: TestClass

I also tried with a small example (the source code is below), and I get the same error, please someone have an idea why I get this error?

main.cpp

#include <QtGui/QApplication>
#include <QtDeclarative>
#include "qmlapplicationviewer.h"
#include "testclass.h"

Q_DECL_EXPORT int main(int argc, char *argv[])
{
    QScopedPointer<QApplication> app(createApplication(argc, argv));
    
    TestClass testClass;

    QmlApplicationViewer *viewer = new QmlApplicationViewer();

    QDeclarativeContext *context = viewer->rootContext();
    context->setContextProperty("TestClass", &testClass);
    viewer->setMainQmlFile(QLatin1String("qml/test022/main.qml"));
    viewer->showExpanded();

    return app->exec();
}

testclass.h

#ifndef TESTCLASS_H
#define TESTCLASS_H

#include <Qt>
#include <QObject>
#include <QDebug>
#include <QtDeclarative>


class TestClass : public QObject
{
    Q_OBJECT
public:
    TestClass(){}
    Q_INVOKABLE QString showText(QString txt){

        qDebug() << txt;

        QDeclarativeEngine *engine = new QDeclarativeEngine;
        QDeclarativeComponent component(engine, QUrl::fromLocalFile("qml/test022/MainPage.qml"));
        if (component.status() == 1){
            QObject *object = component.create();
            QVariant returnedValeur;
            QVariant msg = "002";
            QMetaObject::invokeMethod(object, "jsFunction",Q_RETURN_ARG(QVariant, returnedValeur), Q_ARG(QVariant, msg));
            qDebug() << returnedValeur.toString();
        }
        engine->deleteLater();
        return "OK";
    }
};

#endif // TESTCLASS_H

main.qml

import QtQuick 1.1
import com.nokia.symbian 1.1
import com.nokia.extras 1.1

PageStackWindow {
    id: window
    initialPage: MainPage {tools: toolBarLayout}
    showStatusBar: true
    showToolBar: true

    ToolBarLayout {
        id: toolBarLayout
        ToolButton {
            flat: true
            iconSource: "toolbar-back"
            onClicked: window.pageStack.depth <= 1 ? Qt.quit() : window.pageStack.pop()
        }
    }
}

MainPage.qml

import QtQuick 1.1
import com.nokia.symbian 1.1
import com.nokia.extras 1.1

Page {
    id: mainPage

    function jsFunction(jsVar){
        console.log(jsVar)
        return "003"
    }

    Text {
        anchors.centerIn: parent
        text: qsTr("Hello world!")
        color: platformStyle.colorNormalLight
        font.pixelSize: 20
    }
    Component.onCompleted: TestClass.showText("001")
}

[vineet.jain]

A work around is given here which you can try : http://stackoverflow.com/questions/8...ml-on-nokia-n9

[aymen_ka]

Hi, thank you for your response
But I tried this and it doesn't work, I get the same error

[vineet.jain]

I think TestClass will only be visible in main.qml & not in MainPage.qml. What happens if you try accessing TestClass in main.qml?

[aymen_ka]

Correct, I can access to TestClass in main.qml without errors, but how I can access to it from MainPage.qml ?

[vineet.jain]

You can refer here as how c++ is exposed from qml : http://xizhizhu.blogspot.in/2010/10/...-and-qt-c.html

Basically you need to set the context property for the same view(for same qml) which is being loaded next. So, going by this, set the context property for MainPage.qml as well before launching it.

[aymen_ka]

You can refer here as how c++ is exposed from qml : http://xizhizhu.blogspot.in/2010/10/...-and-qt-c.html

Basically you need to set the context property for the same view(for same qml) which is being loaded next. So, going by this, set the context property for MainPage.qml as well before launching it.

Hi again Jain,
How I can set the context property for MainPage.qml as well as for main.qml? I doesn't found how I can do this in the link

[vineet.jain]

When you create the MainPage.qml using let say QDeclarativeComponent , at the same time you need to set the context property for that view which will expose the c++ class to that qml class.

QDeclarativeEngine engine;
QDeclarativeComponent component(&engine, QUrl::fromLocalFile("qml/test022/MainPage.qml"));
QDeclarativeContext *context = engine()->rootContext();
context->setContextProperty("TestClass", this);
QObject *object = component.create();

[aymen_ka]

Thank you again Jain,
Finally I found the source of the error, I need to added a latency timer to wait the creation of the Component.
I just changed the MainPage.qml as below and all works without errors now:

import QtQuick 1.1
import com.nokia.symbian 1.1
import com.nokia.extras 1.1

Page {
    id: mainPage

    function jsFunction(jsVar){
        console.log(jsVar)
        return "003"
    }

    Text {
        anchors.centerIn: parent
        text: qsTr("Hello world!")
        color: platformStyle.colorNormalLight
        font.pixelSize: 20
    }

    Timer{
        id: timer
        interval: 10
        repeat: false
        running: false
        onTriggered: TestClass.showText("001")
    }

    Component.onCompleted: timer.start()
}