CODEWITHSUNDEEP
qtqml
Alexander Gulchenko
Alexander Gulchenko

Reputation: 303

QML: Unable to assign [undefined] to

I'm trying to rewrite interface for a Qt-Android program from QWidgets to QML. I never used it earlier so mistakes could be very obvious and dumb.

New interface is based on ListView:

It looks like:

ListView
{
    id: listView
    x: 16
    y: 146
    width: 262
    height: 282
    model: myModel
    delegate: Item
    {
        x: 5
        width: 80
        height: 40
        Row
        {
            id: row1
            spacing: 10
            Text
            {
                width: 50
                text:model.modelData.getPassword
                font.bold: true
                anchors.verticalCenter: parent.verticalCenter
            }
            ProgressBar
            {
                value: model.modelData.getDifficulty
            }
        }
    }
}

List in main() is filled this way:

QList<QObject*> dataList;
dataList.append(new DataObject("Item 1", 50));
dataList.append(new DataObject("Item 2", 60));
dataList.append(new DataObject("Item 3", 70));
dataList.append(new DataObject("Item 4", 80));


QGuiApplication app(argc, argv);
qmlRegisterType<BackEnd>("tk.asciigames.backend", 1, 0, "BackEnd");

QQmlApplicationEngine engine;

engine.rootContext()->setContextProperty("myModel", QVariant::fromValue(dataList));

engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

return app.exec();

DataObject:

class DataObject : public QObject
{
    Q_OBJECT

    Q_PROPERTY(QString password         READ getPassword)
    Q_PROPERTY(unsigned int difficulty  READ getDifficulty)
public:
   DataObject(QString _pass, unsigned int _difficulty)
{
    difficulty = _difficulty;
    password = _pass;
}

QString getPassword()
{
    return password;
}

unsigned int getDifficulty()
{
    return difficulty;
}

private:
unsigned int    difficulty;
QString         password;

};

While running QML really shows 4 lines(as expected) but without data. Log has such errors:

qrc:/main.qml:118:26: Unable to assign [undefined] to QString
qrc:/main.qml:124:28: Unable to assign [undefined] to double

Those errors corresponds to QML-lines:

text:model.modelData.getPassword
value: model.modelData.getDifficulty

So it looks like QML gets the array but not able to get data from it.

Can somebody help me to find a mistake?

Upvotes: 5

Views: 17152

Answers (1)

Yoann Quenach de Quivillic
Yoann Quenach de Quivillic

Reputation: 5326

When you declare the Q_PROPERTY, you define a name, and a getter function. The getter function is used by the c++ to get the actual value of the property, but the QML engine has no knowledge of it ; it only knows the property name (password in this example)

Q_PROPERTY(QString password READ getPassword)

So, in your QML file, change the lines

text:model.modelData.getPassword
value: model.modelData.getDifficulty

to

text:model.modelData.password
value: model.modelData.difficulty

And you should be good to go.

Note that you can also use a shortened syntax to access the properties

value: model.modelData.difficulty // OK
value: model.difficulty // OK
value: modelData.difficulty // OK
value: difficulty // Still OK
value: model.model.model.model.model.modelData.difficulty // OK, but don't do that

You may also want to flag your Q_PROPERTY as CONSTANT, to get rid of the warning QQmlExpression: Expression qrc:/main.qml:25:20 depends on non-NOTIFYable properties:

Q_PROPERTY(QString password READ getPassword CONSTANT)

Upvotes: 7

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