[Qt-qml] Q_INVOKABLE member function: Valid argument types

[Jonathan Zhong]

Thanks! This is exactly the Qt documentation page I had been looking 
for. My prior experimentation appears to support what the documentation 
says.

There is one remaining issue: Since int * as an argument does not appear 
working, what if I need to get more than one output integers from the 
Q_INVOKABLE function?

That is, since the following may not work:

// !!! This Q_INVOKABLE function does not work:
void MyClass::myFunc4(int * myOutputInt1, int * myOutputInt2)
{
     *myOutputInt1 = 11111;
     *myOutputInt2 = 22222;
}

one solution is to package the 2 output integers into an object of a Qt 
class that is recognizable by QML, for example, QVariant, as illustrated 
below:

// This Q_INVOKABLE function appears working:
QVariant MyClass::myFunc5()
{
     int myOutputInt1 = 11111;
     int myOutputInt2 = 22222;

     QScriptEngine engine;

     QScriptValue value = engine.newObject();
     value.setProperty("myOutputInt1", myOutputInt1);
     value.setProperty("myOutputInt2", myOutputInt2);

     return value.toVariant();
}

And in my QML code, I'll do something like this:

var myVariant = myClassObject.myFunc5();
var myInt1 = myVariant.myOutputInt1;
var myInt2 = myVariant.myOutputInt2;

This, although it works, does not look simple and straightforward. Is 
there a better way?


On 10/11/2011 11:02 AM, Girish Ramakrishnan wrote:
> Hi Jonathan,
>
> On Tue, Oct 11, 2011 at 10:36 PM, Jonathan Zhong
> <jonathan.zhong at panasonic.aero>  wrote:
>> Hi,
>>
>> What are the valid argument types of an invokable member function of a
>> QML extension C++ class? I have noticed that these work:
>>
>> Q_INVOKABLE void myFunc1(int myInputInt);
>> Q_INVOKABLE void myFunc2(int&  myInputInt);    // but myInputInt cannot
>> be modified.
>>
>> while this does not work:
>>
>> Q_INVOKABLE void myFunc3(int * myOutputInt);    // This will cause a
>> runtime error when running qmlviewer.
>>
>> It appears that:
>> 1. The argument can be an object of (or reference to) a basic C/C++ data
>> type (int, int&, double, double&, ...).
>> 2. The argument can be an object or (or reference to) a Qt class which
>> relates to a basic QML type (QString, QString&, QVariant, QVariant&, ..).
>> 3. The argument can be a pointer to QObject or its derived classes
>> (QObject *, QWidget *, ...).
>> ...
>>
>> Is there a Qt documentation page on this subject?
>>
>> Perhaps this is a related question: What are the valid return types of
>> an invokable member function?
>>
> See http://doc.qt.nokia.com/main-snapshot/qtbinding.html#supported-data-types
>
> Girish



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