wxObjectRefData Class Reference

#include <wx/object.h>

Inheritance diagram for wxObjectRefData:

Detailed Description

This class is just a typedef to wxRefCounter and is used by wxObject.

Derive classes from this to store your own data in wxObject-derived classes. When retrieving information from a wxObject's reference data, you will need to cast to your own derived class.

Below is an example illustrating how to store reference counted data in a class derived from wxObject including copy-on-write semantics.

Example

// include file
// ------------

class MyCar : public wxObject
{
public:
    MyCar() { }
    MyCar( int price );

    bool IsOk() const { return m_refData != NULL; }

    bool operator == ( const MyCar& car ) const;
    bool operator != (const MyCar& car) const { return !(*this == car); }

    void SetPrice( int price );
    int GetPrice() const;

protected:
    virtual wxObjectRefData *CreateRefData() const;
    virtual wxObjectRefData *CloneRefData(const wxObjectRefData *data) const;

    wxDECLARE_DYNAMIC_CLASS(MyCar)
};


// implementation
// --------------

// the reference data class is typically a private class only visible in the
// implementation source file of the refcounted class.
class MyCarRefData : public wxObjectRefData
{
public:
    MyCarRefData()
    {
        m_price = 0;
    }

    MyCarRefData( const MyCarRefData& data )
        : wxObjectRefData()
    {
        // copy refcounted data; this is usually a time- and memory-consuming operation
        // and is only done when two (or more) MyCar instances need to unshare a
        // common instance of MyCarRefData
        m_price = data.m_price;
    }

    bool operator == (const MyCarRefData& data) const
    {
        return m_price == data.m_price;
    }

private:
    // in real world, reference counting is usually used only when
    // the wxObjectRefData-derived class holds data very memory-consuming;
    // in this example the various MyCar instances may share a MyCarRefData
    // instance which however only takes 4 bytes for this integer!
    int m_price;
};


#define M_CARDATA ((MyCarRefData *)m_refData)
wxIMPLEMENT_DYNAMIC_CLASS(MyCar, wxObject);

MyCar::MyCar( int price )
{
    // here we init the MyCar internal data:
    m_refData = new MyCarRefData();
    M_CARDATA->m_price = price;
}

wxObjectRefData *MyCar::CreateRefData() const
{
    return new MyCarRefData;
}

wxObjectRefData *MyCar::CloneRefData(const wxObjectRefData *data) const
{
    return new MyCarRefData(*(MyCarRefData *)data);
}

bool MyCar::operator == ( const MyCar& car ) const
{
    if (m_refData == car.m_refData)
        return true;
    if (!m_refData || !car.m_refData)
        return false;

    // here we use the MyCarRefData::operator==() function.
    // Note however that this comparison may be very slow if the
    // reference data contains a lot of data to be compared.
    return ( *(MyCarRefData*)m_refData == *(MyCarRefData*)car.m_refData );
}

void MyCar::SetPrice( int price )
{
    // since this function modifies one of the MyCar internal property,
    // we need to be sure that the other MyCar instances which share the
    // same MyCarRefData instance are not affected by this call.
    // I.e. it's very important to call UnShare() in all setters of
    // refcounted classes!
    UnShare();

    M_CARDATA->m_price = price;
}

int MyCar::GetPrice() const
{
    wxCHECK_MSG( IsOk(), -1, "invalid car" );

    return M_CARDATA->m_price;
}

Library:  wxBase

Category:  Runtime Type Information (RTTI)

See Also

wxObject, wxObjectDataPtr<T>, Reference Counting