Unknown method parameter type: QString&

[liubbc]

Hi， Qters

When QML call C++ class function, an error occur :
Unknown method parameter type: QString&

The code snippet are :

//calculator.h 
class Calculator : public QObject{
        public: 
        Q_INVOKABLE QString getResult(QString & leftValue, QString & rightValue);
}

//calculator.cpp
QString Calculator::getResult(QString & leftValue, QString & rightValue){
    return "abc";
}

//qml

Calculator{
        id: calculator;
    }

display.text = calculator.getResult("abc", "bcd");

if class Calculator getResult function is defined :

class Calculator : public QObject{
        public: 
        Q_INVOKABLE QString getResult(QString  leftValue, QString  rightValue);
}

the error disappeared.

but i do not know the root cause. Does anybody know the reason ? Thanks in advance !

[edit: sierdzio. Added code tags]

[sierdzio]

QML connections are handled via MOC in Qt, which places strict rules on parameters - to prevent problems in threads. More info.

When a function is called via Q_INVOKABLE (or it is a slot), parameter is always passed by value (copy ). Const references also work.

[liubbc]

Many thanks！

[Alien]

Dear @liubbc,
Could you please mark this topic to SOLVED
Thanks a lot ;)

[liubbc]

@sierdzio Many Thanks

[liubbc]

@Alien So sorry， i try many times , but how to translate UNSOLVED to SOLVED ?

[Alien]

@liubbc your welcome,
click on "Topic Tools" button on right bottom of the page and then select the "Mark as solved"
have a nice day