[Interest] C++/QML: Plugin loads, Q_INVOKABLE works, no properties

[Charley Bay]

I wrote a C++ plugin that exposes a C++ "MyCppClass" for QML. The
"Q_INVOKABLE" members work, but I cannot "see" any "Q_PROPERTY" values for
the *same* instance.

Assume a trivial "MyCppClass":

//-----------
class MyCppClass : public QObject {
  Q_OBJECT
  Q_PROPERTY(int value READ value WRITE setValue NOTIFY valueChanged)
public:
  MyCppClass();
  virtual ~MyCppClass();
  Q_INVOKABLE void myInvokeFunc();
  int value();
  void setValue(int i);
signals:
  void valueChanged(int);
private:
  int m_iValue;
};
//-----------

Example QML use:

//-----------
// FILE: MyQml.qml
import QtQuick 2.1
import QtQuick.Controls 1.0
import QtQuick.Window 2.0

import MyCppPlugin 1.0

Item {
  MyCppClass {      //<==OK
     id: myClass      //<==OK
     value: 42          //<==QML LOAD ERROR
  }

  Button {
    text: "Hello"
    onClicked: {
      myClass.myInvokeFunc()   //<==OK
    }
}
//-----------

What's going on:

*- SUCCESS:  C++ Plugin loads through QML "import"
*- SUCCESS:  Instantiating a C++ object in QML
*- SUCCESS:  Calling "Q_INVOKABLE" function from QML
*- FAIL:  Accessing any properties in QML from that *same* C++ object (QML
fails to load, error:  "Cannot assign to non-existent property "value"")
.... assigning/binding fails to load the QML file, and "reading" any
property results in "undefined")

This doesn't make sense to me (Qt 5.1.1, Win7).  The plugin loads, the C++
object is instantiated, the "Q_INVOKABLE" function works, but I apparently
cannot "see" any "Q_PROPERTY" values.

QUESTION:  What are the possible scenarios where "Q_INVOKABLE" works on an
instance, but "Q_PROPERTY" properties are still unavailable for that *same*
instance?

--charley

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