Q_PROPERTY READ overloaded function - qt

Question

I have my C++/QT code
// .hpp
Q_PROPERTY(int Index READ Index WRITE setIndex NOTIFY IndexChanged)
public:
int Index() const;
int Index(int n) const;
void setIndex(int index):
//.cpp
setContextProperty(QStringLiteral("target"), this)
On the QML side i can access the index using target.Index. What is the syntax for using the taget.Index(int n) for example target.Index(8) gives me errors. Any examples for overloaded read function ?

Answer 1

What you are trying to do is sadly not really possible;
To begin with you'd need to add Q_INVOKABLE to the overloaded method (or make it a slot) in order to make it available to the QML engine:
Q_INVOKABLE int Index(int n) const;
That would mean that target.index is both a function and an int though, and that's of course not possible (isn't in QML/JavaScript and neither in C++). Qt seems to give priority to the property in this case, so you'll still get the "...is not a function" error.
You'll probably have to rename the overloaded function.
Note: The QML engine does handle function overloads (just make sure they are all either slots or marked with Q_INVOKABLE), just not having a function and a property of the same name. So you could have both target.Index() and target.Index(4), but you can't notify of changes that way.

Answer 2

There are two possible approaches:
You should:
Disambiguate the names exposed to QML.
Expose the method not given in Q_PROPERTY as invokable.
E.g.:
class Foo : public QObject {
Q_OBJECT
Q_PROPERTY(int Index READ Index WRITE setIndex NOTIFY IndexChanged)
// QML Interface
Q_INVOKABLE int Index1(int n) const { return Index(n); }
public:
// C++ interface
int Index() const;
int Index(int n) const;
void setIndex(int index);
Q_SIGNAL void IndexChanged();
};
Alternatively, if you're OK with using function interface from JavaScript in place of property interface, you need to take an optional argument via a QVariant. See this question for further details about overloading in QML. E.g.:
class Foo : public QObject {
Q_OBJECT
Q_PROPERTY(int IndexProp READ Index WRITE setIndex NOTIFY IndexChanged)
// QML interface
Q_INVOKABLE int Index(const QVariant & n) const {
if (n.isValid())
return Index(n.toInt());
return Index();
}
public:
// C++ interface
int Index() const;
int Index(int n) const;
void setIndex(int index);
Q_SIGNAL void IndexChanged();
};
The following are all valid then:
target.IndexProp = 5
foo = target.IndexProp
foo = target.Index()
foo = target.Index(2)