[SOLVED]Q_PROPERTY QString linking qml and c++ giving "undefined" error

Billcode

This simple example should test the linking between QObject class property and qml. A string from TextInput should get displayed in a Rectangle on a mouse click. Instead, an error - Cannot assign [undefined] to QString - is delivered. Could anyonw help?

@//mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QDeclarativeView>
#include <QObject>
#include <QString>

class MainWindow : public QDeclarativeView
{
Q_OBJECT

public:
MainWindow(QWidget *parent = 0);
~MainWindow();
};

class Data : public QObject
{
Q_OBJECT
Q_PROPERTY(QString teamName READ getTeamName WRITE setTeamName NOTIFY nameChanged)

public: Data(QObject *parent = 0);

QString getTeamName() const;
void setTeamName(const QString &newString);

signals:
void nameChanged(QString &);

private:
QString newTeam;
};

#endif // MAINWINDOW_H@

@//mainwindow.cpp
#include "mainwindow.h"
#include <QDeclarativeView>
#include <QObject>
#include <QString>

MainWindow::MainWindow(QWidget *parent)
: QDeclarativeView(parent)
{

}

MainWindow::~MainWindow()
{

}

Data::Data(QObject *parent) : QObject(parent)
{

}

QString Data::getTeamName() const{
return newTeam;
}

void Data::setTeamName(const QString &newString){
if(newString != newTeam)
{
newTeam = newString;
emit nameChanged(newTeam);
}
}@

@//main.cpp
#include "mainwindow.h"
#include "qdeclarative.h"
#include <QApplication>
#include <QDeclarativeView>
#include <QDeclarativeContext>

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
qmlRegisterType<Data>("NData", 1, 0, "Data");
w.setSource(QUrl::fromLocalFile("../subor1/Main.qml"));

Data d;
w.rootContext()->setContextProperty("data", &d);

w.show();

return a.exec(&#41;;

}@

@//Main.qml
import QtQuick 1.1
import NData 1.0

Rectangle {
id: root

Rectangle{
    id: textIn
    ...
    TextInput{
        id: tIn
        text: ""
    }
}
Rectangle{
    id: textOut
    ...
    Text{
        id: tOut
        anchors.centerIn: textOut
        text: ""
    }
}
Rectangle{
    id: textClick
    ...
    Text{
        id: tcText
        anchors.centerIn: textClick
        text: "Click"
    }
    MouseArea{
        id: tcMouse
        anchors.fill: textClick
        onClicked: {
            data.teamName = tIn.text
            tOut.text = data.teamName
        }
    }
}

}@

melghawi

"data":http://qt-project.org/doc/qt-5.0/qtquick/qml-qtquick2-item.html#data-prop is one of the properties of the qml "Item":http://qt-project.org/doc/qt-5.0/qtquick/qml-qtquick2-item.html component.

Try changing this:

@
w.rootContext()->setContextProperty("data", &d);
@

to this:

@
w.rootContext()->setContextProperty("dataProvider", &d);
@

Also, make sure you set your context property before creating your scene.

@
Data d;
// You must do this....
w.rootContext()->setContextProperty("dataProvider", &d);

// before doing this
w.setSource(QUrl::fromLocalFile("../subor1/Main.qml"));
@

Also, if you do not need to create an instance of your Data class from qml then maybe you should change this:

@
qmlRegisterType<Data>("NData", 1, 0, "Data");
@

to this:

@
qmlRegisterType<Data>();
@

Also, if the purpose of your Data class is to export data from c++ to qml only then have a look at the solution posted "here":http://qt-project.org/forums/viewthread/26191/. It shows you how to create a singleton class that is used to export data from c++ to qml. There is both a QQuick 1.0 and 2.0 solution.

Billcode

Thanks a lot! It really works as supposed now. Thank You.