How to pass QList from QML to C++/Qt?

Question

I'm trying to pass QList of integer from QML to C++ code, but somehow my approach is not working. With below approach am getting following error:

left of '->setParentItem' must point to class/struct/union/generic type
type is 'int *'

Any inputs to trouble shoot the issue is highly appreciated

Below is my code snippet

Header file

Q_PROPERTY(QDeclarativeListProperty<int> enableKey READ enableKey) 

QDeclarativeListProperty<int> enableKey(); //function declaration
QList<int> m_enableKeys;

cpp file

QDeclarativeListProperty<int> KeyboardContainer::enableKey()
{
    return QDeclarativeListProperty<int>(this, 0, &KeyboardContainer::append_list);
}

void KeyboardContainer::append_list(QDeclarativeListProperty<int> *list, int *key)
{
    int *ptrKey = qobject_cast<int *>(list->object);
    if (ptrKey) {
        key->setParentItem(ptrKey);
        ptrKey->m_enableKeys.append(key);
    }
}

`setParentItem` and `m_enableKeys` are not members of `int`, but you try to invoke them on key and ptrKey which are both int* so that will never work.. — stijn, Dec 19 '12 at 10:45
remember that `QDeclarativeListProperty` / `QQmlListProperty` is only useful for supplying a readonly list of sub items that are QObject derived ones, and that list can not be modified after instanciation time. — TheBootroo, Mar 27 '13 at 10:46

TheBootroo · Accepted Answer · 2013-03-26T16:26:41.090

You CAN'T use QDeclarativeListProperty (or QQmlListProperty in Qt5) with any other type than QObject derived ones. So int or QString will NEVER work.

If you need to exchange a QStringList or a QList or anything that is an array of one of the basic types supported by QML, the easiest way to do it is to use QVariant on the C++ side, like this :

#include <QObject>
#include <QList>
#include <QVariant>

class KeyboardContainer : public QObject {
    Q_OBJECT
    Q_PROPERTY(QVariant enableKey READ   enableKey
               WRITE  setEnableKey
               NOTIFY enableKeyChanged)

public:
    // Your getter method must match the same return type :
    QVariant enableKey() const {
        return QVariant::fromValue(m_enableKey);
    }

public slots:
    // Your setter must put back the data from the QVariant to the QList<int>
    void setEnableKey (QVariant arg) {
        m_enableKey.clear();
        foreach (QVariant item, arg.toList()) {
            bool ok = false;
            int key = item.toInt(&ok);
            if (ok) {
                m_enableKey.append(key);
            }
        }
        emit enableKeyChanged ();
    }

signals:
    // you must have a signal named <property>Changed
    void enableKeyChanged();

private:
    // the private member can be QList<int> for convenience
    QList<int> m_enableKey;
};

On the QML side, simply affect a JS array of Number, the QML engine will automatically convert it to QVariant to make it comprehensible to Qt :

KeyboardContainer.enableKeys = [12,48,26,49,10,3];

That's all !

But... what about this document? http://qt-project.org/doc/qt-5.0/qtqml/qtqml-cppintegration-data.html — S.M.Mousavi, Sep 09 '13 at 13:34
In the above documentation, there is transparent support for QList and QListString and QList and some other sequences — S.M.Mousavi, Sep 09 '13 at 14:02

How to pass QList from QML to C++/Qt?

1 Answers1