How to use Q_DECLARE_METATYPE

[lni]

Hi,

My object is derived from QObject, which have copy construction and assignment op disable.

I try to let QVairant know it by using:
Q_DECLARE_METATYPE(MyClass *)

In another class that has a member field of the MyClass, and I define as:
Q_PROPERTY( MyClass* tvd READ tvd WRITE setTVD )

However, when reading the obj use QMetaProperty::read( obj ), it complains
QMetaProperty::read: Unable to handle unregistered datatype "MyClass*' for property..

How do I actually register a pointer?

Thanks

[lni]

The codes look like:

class ClassA : public QObject
{
  Q_OBJECT
...
}
Q_DECLARE_METATYPE( ClassA*)
 
class ClassB : public QObject
{
  Q_OBJECT
  Q_PROPERTY( ClassA* A READ getA WRITE setA)
 
public:
 
  ClassA* getA() const { return A;}
  void setA( ClassA* a ) {A = a; }
 
private:
 
  ClassA*                 A;
 
}

class ClassA : public QObject
{
  Q_OBJECT
...
}
Q_DECLARE_METATYPE( ClassA*)

class ClassB : public QObject
{
  Q_OBJECT
  Q_PROPERTY( ClassA* A READ getA WRITE setA)

public:

  ClassA* getA() const { return A;}
  void setA( ClassA* a ) {A = a; }

private:

  ClassA*                 A;

}

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The somewhere I try to read the property property.read( ClassB_Object )

When enter getA(), it starts to complain.

Any hint is higely appreciated.

[lni]

Can anyone help, please? Thanks

[lni]

bump bump bump

[jpn]

qRegisterMetaType<ClassA*>("ClassA*");

qRegisterMetaType<ClassA*>("ClassA*");

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[lni]

qRegisterMetaType<ClassA*>("ClassA*");

qRegisterMetaType<ClassA*>("ClassA*");

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Thanks.

Then how can I construct the object as:

int id = QMetaType::type("ClassA") or QMetaType::type("ClassA*");
void* obj = QMetaType::construct( id );
ClassA* a = static_cast<ClassA*>( obj );

int id = QMetaType::type("ClassA") or QMetaType::type("ClassA*");
void* obj = QMetaType::construct( id );
ClassA* a = static_cast<ClassA*>( obj );

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My ClassA doesn't have copy constructor (disabled).

I have tried the follow codes, the copy constructor or operator= are never called, why copy constructor are required here? Thank you!

class MyStruct {
public:
  MyStruct();
  MyStruct( const MyStruct& );
  MyStruct& operator=( const MyStruct& );
};
 
MyStruct::MyStruct()
{
  std::cout << "In constructor" << std::endl;
}
 
MyStruct::MyStruct( const MyStruct& org )
{
  std::cout << "In copy constructor" << std::endl;
}
 
MyStruct& MyStruct::operator=( const MyStruct& rhs )
{
  std::cout << "operator=" << std::endl;
  return *this;
}
int main()
{
  qRegisterMetaType<MyStruct>( "MyStruct" );
  int id = QMetaType::type("MyStruct");
  void* obj = QMetaType::construct( id );
}

class MyStruct {
public:
  MyStruct();
  MyStruct( const MyStruct& );
  MyStruct& operator=( const MyStruct& );
};

MyStruct::MyStruct()
{
  std::cout << "In constructor" << std::endl;
}

MyStruct::MyStruct( const MyStruct& org )
{
  std::cout << "In copy constructor" << std::endl;
}

MyStruct& MyStruct::operator=( const MyStruct& rhs )
{
  std::cout << "operator=" << std::endl;
  return *this;
}
int main()
{
  qRegisterMetaType<MyStruct>( "MyStruct" );
  int id = QMetaType::type("MyStruct");
  void* obj = QMetaType::construct( id );
}

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[RThaden]

From the docs:

int qRegisterMetaType ( const char * typeName )

Registers the type name typeName to the type T. Returns the internal ID used by QMetaType. Any class or struct that has a public constructor, a public copy constructor, and a public destructor can be registered.

If you use queued signal-slot connections, the parameters of the signals/slots have to be stored somewhere since the slot is delivered within the event loop at a later time.
That's why the copy-constructor is needed.

Regards,

Rainer