How to properly use qRegisterMetaType on a class derived from QObject?

Question

I\'ve been searching far and wide for an answer to this but to no avail. My lament is as follows:

I have a ClassA that roughly looks like this:

Answer 1

A few things:

• The reason that registering ClassA* isn't working is because your call to construct() is constructing a pointer to a ClassA object, but not an actual object.

• It is worthy of noting the following quote from the QMetaType documentation:

Any class or struct that has a public default constructor, a public copy constructor, and a public destructor can be registered.

• Take a look at Qt's implementation of qMetaTypeConstructHelper:

  template 
  void *qMetaTypeConstructHelper(const T *t)
  {
      if (!t)
          return new T();
      return new T(*static_cast(t));
  }
  

and note their usage of the copy constructor. This being the case, you have two ways around the problem:

1) Provide a copy constructor (which you have done)

2) Provide a specialization of qMetaTypeConstructHelper that doesn't use the copy constructor:

template <>
void *qMetaTypeConstructHelper(const ClassA *)
{
    return new ClassA();
}