Using Qt Properties with custom types defined in namespaces

Question

I have currently a problem when using an own type as property type.

My custom type is defined within a namespace. When I put it into the global namespace, everything works without any problems.

Is it possible to use custom types within a namespace as property values?

Here's a minimum example (I am using Qt5.0 and g++ 4.7.3)

Here's the test.pro file:

LANGUAGE  = C++
QT += core gui widgets
TARGET = test
QMAKE_CXXFLAGS += -std=c++11
HEADERS += test.h
SOURCES += test.cpp

Here's the test.h file:

#include <QtCore>
#include <QtGui>
#include <QtWidgets>

namespace MyNamespace
{
  struct MyValue
  {
  private:
    QString a;
    int b;

  public:
    MyValue(const QString &a="", int b=0)
      : a(a), b(b)
    {
    }

    bool operator !=(const MyValue &other) const
    {
      return (this->a!=other.a) || (this->b!=other.b);
    }

    friend QDataStream &operator<<(QDataStream &stream, const MyNamespace::MyValue &value);
    friend QDataStream &operator>>(QDataStream &stream, MyNamespace::MyValue &value);
    friend QDebug operator<<(QDebug debug, const MyNamespace::MyValue &value);
  };

  inline QDataStream &operator<<(QDataStream &stream, const MyNamespace::MyValue &value)
  {
    stream << value.a;
    return stream << value.b;
  }

  inline QDataStream &operator>>(QDataStream &stream, MyNamespace::MyValue &value)
  {
    stream >> value.a;
    return stream >> value.b;
  }

  inline QDebug operator<<(QDebug debug, const MyNamespace::MyValue &value)
  {
    return debug << "MyValue("<<value.a<<", "<<value.b<<")";
  }
}

Q_DECLARE_METATYPE(MyNamespace::MyValue)


namespace AnotherNamespace
{
  typedef MyNamespace::MyValue MyValue;

  class MyClass : public QObject
  {
    Q_OBJECT

    Q_PROPERTY(MyValue value READ value WRITE setValue NOTIFY valueChanged)

  public:
    MyValue value()
    {
      return value_;
    }

  public slots:
    void setValue(const MyValue &value)
    {
      if(this->value() != value)
      {
        value_ = value;
        emit valueChanged(value);
      }
    }

  signals:
    void valueChanged(const MyValue &value);

  private:
    MyValue value_;
  };

}

And here's the test.cpp file:

#include "test.h"

int main(int argc, char** argv)
{
  QApplication app(argc, argv);

  qRegisterMetaTypeStreamOperators<MyNamespace::MyValue>("MyNamespace::MyValue");


  AnotherNamespace::MyClass myObject;

  myObject.setValue(MyNamespace::MyValue("the answer", 42));

  QMetaObject metaObject = AnotherNamespace::MyClass::staticMetaObject;
  QMetaProperty metaProperty = metaObject.property(metaObject.indexOfProperty("value"));
  QVariant variant = metaProperty.read(&myObject);

  MyNamespace::MyValue value = variant.value<MyNamespace::MyValue>();

  qDebug() << value;


  qDebug() << "\nIt's interesting, that this is working without problems:";
  variant = QVariant::fromValue(MyNamespace::MyValue("2^4", 16));
  value = variant.value<MyNamespace::MyValue>();

  qDebug() << value;


  return 0;
}

The output of this minimum example is

QMetaProperty::read: Unable to handle unregistered datatype 'MyValue' for property 'AnotherNamespace::MyClass::value'
MyValue( "" ,  0 ) 

It's interesting, that this is working without problems: 
MyValue( "2^4" ,  16 ) 

As alreaday said, after removing any namespace usage from the minimum example, everything works without any problems with the following output

MyValue( "the answer" ,  42 ) 

It's interesting, that this is working without problems: 
MyValue( "2^4" ,  16 ) 

Answer 1

While typing in the question I've found the answer. The error is in the following lines

// ...
namespace AnotherNamespace
{
  typedef MyNamespace::MyValue MyValue;

  class MyClass : public QObject
  {
    Q_OBJECT

    Q_PROPERTY(MyValue value READ value WRITE setValue NOTIFY valueChanged)
// ...

When using the Q_PROPERTY I have to give the full typename with all namespaces noted. So instead of using

Q_PROPERTY(MyValue value READ value WRITE setValue NOTIFY valueChanged)

I have to use

Q_PROPERTY(MyNamespace::MyValue value READ value WRITE setValue NOTIFY valueChanged)

the Qt Property system doesn't seem to recognize typedefs.