wxObjectRefData Class Reference

#include </home/zeitlin/src/wx/github/interface/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.

例

    // 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)

参照:

wxObject, wxObjectDataPtr<T>, Reference Counting