include/wx/weakref.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        wx/weakref.h
   3 // Purpose:     wxWeakRef - Generic weak references for wxWidgets
   4 // Author:      Arne Steinarson
   5 // Created:     27 Dec 07
   6 // RCS-ID:      $Id$
   7 // Copyright:   (c) 2007 Arne Steinarson
   8 // Licence:     wxWindows licence
   9 /////////////////////////////////////////////////////////////////////////////
  10
  11 #ifndef _WX_WEAKREF_H_
  12 #define _WX_WEAKREF_H_
  13
  14 #include "wx/tracker.h"
  15
  16 #include "wx/meta/convertible.h"
  17 #include "wx/meta/int2type.h"
  18
  19 template <class T>
  20 struct wxIsStaticTrackable
  21 {
  22     enum { value = wxConvertibleTo<T, wxTrackable>::value };
  23 };
  24
  25 // Weak ref implementation when T has wxTrackable as a known base class
  26 template <class T>
  27 class wxWeakRefStatic : public wxTrackerNode
  28 {
  29 public:
  30     wxWeakRefStatic() : m_pobj(NULL) { }
  31
  32     void Release()
  33     {
  34         // Release old object if any
  35         if ( m_pobj )
  36         {
  37             // Remove ourselves from object tracker list
  38             wxTrackable *pt = static_cast<wxTrackable*>(m_pobj);
  39             pt->RemoveNode(this);
  40             m_pobj = NULL;
  41         }
  42     }
  43
  44 protected:
  45     void Assign(T* pobj)
  46     {
  47         if ( m_pobj == pobj )
  48             return;
  49
  50         Release();
  51
  52         // Now set new trackable object
  53         if ( pobj )
  54         {
  55             // Add ourselves to object tracker list
  56             wxTrackable *pt = static_cast<wxTrackable*>(pobj);
  57             pt->AddNode(this);
  58             m_pobj = pobj;
  59         }
  60     }
  61
  62     void AssignCopy( const wxWeakRefStatic& wr )
  63     {
  64         Assign( wr.m_pobj );
  65     }
  66
  67     virtual void OnObjectDestroy()
  68     {
  69         // Tracked object itself removes us from list of trackers
  70         wxASSERT( m_pobj!=NULL );
  71         m_pobj = NULL;
  72     }
  73
  74     T *m_pobj;
  75 };
  76
  77 #ifdef HAVE_PARTIAL_SPECIALIZATION
  78
  79 template<class T,bool use_static>
  80 struct wxWeakRefImpl;
  81
  82 // Intermediate class, to select the static case above.
  83 template <class T>
  84 struct wxWeakRefImpl<T, true> : public wxWeakRefStatic<T>
  85 {
  86     enum { value = 1 };
  87 };
  88
  89 // Weak ref implementation when T does not have wxTrackable as known base class
  90 template<class T>
  91 struct wxWeakRefImpl<T, false> : public wxTrackerNode
  92 {
  93     void Release()
  94     {
  95         // Release old object if any
  96         if ( m_pobj )
  97         {
  98             // Remove ourselves from object tracker list
  99             m_ptbase->RemoveNode(this);
 100             m_pobj = NULL;
 101             m_ptbase = NULL;
 102         }
 103     }
 104
 105 protected:
 106     wxWeakRefImpl() : m_pobj(NULL), m_ptbase(NULL) { }
 107
 108     // Assign receives most derived class here and can use that
 109     template <class TDerived>
 110     void Assign( TDerived* pobj )
 111     {
 112         AssignHelper( pobj, wxInt2Type<wxIsStaticTrackable<TDerived>::value>() );
 113     }
 114
 115     template <class TDerived>
 116     void AssignHelper(TDerived* pobj, wxInt2Type<true>)
 117     {
 118         wxTrackable *ptbase = static_cast<wxTrackable*>(pobj);
 119         DoAssign( pobj, ptbase );
 120     }
 121
 122 #ifdef HAVE_DYNAMIC_CAST
 123     void AssignHelper(T* pobj, wxInt2Type<false>)
 124     {
 125         // A last way to get a trackable pointer
 126         wxTrackable *ptbase = dynamic_cast<wxTrackable*>(pobj);
 127         if ( ptbase )
 128         {
 129             DoAssign( pobj, ptbase );
 130         }
 131         else
 132         {
 133             wxFAIL_MSG( "Tracked class should inherit from wxTrackable" );
 134
 135             Release();
 136         }
 137     }
 138 #endif // HAVE_DYNAMIC_CAST
 139
 140     void AssignCopy(const wxWeakRefImpl& wr)
 141     {
 142         DoAssign( wr.m_pobj, wr.m_ptbase );
 143     }
 144
 145     void DoAssign( T* pobj, wxTrackable *ptbase ) {
 146         if( m_pobj==pobj ) return;
 147         Release();
 148
 149         // Now set new trackable object
 150         if( pobj )
 151         {
 152             // Add ourselves to object tracker list
 153             wxASSERT( ptbase );
 154             ptbase->AddNode( this );
 155             m_pobj = pobj;
 156             m_ptbase = ptbase;
 157         }
 158     }
 159
 160     virtual void OnObjectDestroy()
 161     {
 162         // Tracked object itself removes us from list of trackers
 163         wxASSERT( m_pobj!=NULL );
 164         m_pobj = NULL;
 165         m_ptbase = NULL;
 166     }
 167
 168     T *m_pobj;
 169     wxTrackable *m_ptbase;
 170 };
 171
 172 #endif // HAVE_PARTIAL_SPECIALIZATION
 173
 174
 175 // A weak reference to an object of type T, where T has type wxTrackable
 176 // (usually statically but if not dynamic_cast<> is tried).
 177 template <class T>
 178 class wxWeakRef : public
 179 #ifdef HAVE_PARTIAL_SPECIALIZATION
 180                   wxWeakRefImpl<T, wxIsStaticTrackable<T>::value>
 181 #else
 182                   wxWeakRefStatic<T>
 183 #endif
 184 {
 185 public:
 186     // Default ctor
 187     wxWeakRef() { }
 188
 189     // When we have the full type here, static_cast<> will always work
 190     // (or give a straight compiler error).
 191     template <class TDerived>
 192     wxWeakRef(TDerived* pobj)
 193     {
 194         Assign(pobj);
 195     }
 196
 197     template <class TDerived>
 198     wxWeakRef<T>& operator=(TDerived* pobj)
 199     {
 200         Assign(pobj);
 201         return *this;
 202     }
 203
 204     wxWeakRef<T>& operator=(const wxWeakRef<T>& wr)
 205     {
 206         AssignCopy(wr);
 207         return *this;
 208     }
 209
 210     virtual ~wxWeakRef() { this->Release(); }
 211
 212     // Smart pointer functions
 213     T& operator*() const { return *this->m_pobj; }
 214     T* operator->() const { return this->m_pobj; }
 215
 216     T* get() const { return this->m_pobj; }
 217     operator T*() const { return get(); }
 218 };
 219
 220
 221 // Weak ref implementation assign objects are queried for wxTrackable
 222 // using dynamic_cast<>
 223 template<class T>
 224 class wxWeakRefDynamic : public wxTrackerNode
 225 {
 226 public:
 227     wxWeakRefDynamic() : m_pobj(NULL) { }
 228
 229     wxWeakRefDynamic(T* pobj) : m_pobj(pobj)
 230     {
 231         Assign(pobj);
 232     }
 233
 234     virtual ~wxWeakRefDynamic() { Release(); }
 235
 236     // Smart pointer functions
 237     T& operator * (){ wxASSERT(this->m_pobj); return *m_pobj; }
 238     T* operator -> (){ wxASSERT(this->m_pobj); return m_pobj; }
 239     T* operator = (T* pobj) { Assign(pobj); return m_pobj; }
 240
 241     T* get(){ return this->m_pobj; }
 242
 243     // operator T* (){ return this->m_pobj; }
 244
 245     // test for pointer validity: defining conversion to unspecified_bool_type
 246     // and not more obvious bool to avoid implicit conversions to integer types
 247     typedef T *(wxWeakRef<T>::*unspecified_bool_type)() const;
 248     operator unspecified_bool_type() const
 249     {
 250         return m_pobj ? &wxWeakRef<T>::get : NULL;
 251     }
 252
 253     // Assign from another weak ref, point to same object
 254     T* operator = (const wxWeakRef<T> &wr) { Assign( wr.get() ); return this->m_pobj; }
 255
 256     void Release()
 257     {
 258         // Release old object if any
 259         if( m_pobj )
 260         {
 261             // Remove ourselves from object tracker list
 262             wxTrackable *pt = dynamic_cast<wxTrackable*>(m_pobj);
 263             wxASSERT(pt);
 264             pt->RemoveNode(this);
 265             m_pobj = NULL;
 266         }
 267     }
 268
 269 protected:
 270     void Assign(T *pobj)
 271     {
 272         if ( m_pobj == pobj )
 273             return;
 274
 275         Release();
 276
 277         // Now set new trackable object
 278         if ( pobj )
 279         {
 280             // Add ourselves to object tracker list
 281             wxTrackable *pt = dynamic_cast<wxTrackable*>(pobj);
 282             if ( pt )
 283             {
 284                 pt->AddNode(this);
 285                 m_pobj = pobj;
 286             }
 287             else
 288             {
 289                 // If the object we want to track does not support wxTackable, then
 290                 // log a message and keep the NULL object pointer.
 291                 wxFAIL_MSG( "Tracked class should inherit from wxTrackable" );
 292             }
 293         }
 294     }
 295
 296     void AssignCopy(const wxWeakRefDynamic& wr)
 297     {
 298         Assign(wr.m_pobj);
 299     }
 300
 301     virtual void OnObjectDestroy()
 302     {
 303         wxASSERT_MSG( m_pobj, "tracked object should have removed us itself" );
 304
 305         m_pobj = NULL;
 306     }
 307
 308     T *m_pobj;
 309 };
 310
 311 // Provide some basic types of weak references
 312 class WXDLLIMPEXP_FWD_BASE wxEvtHandler;
 313 class WXDLLIMPEXP_FWD_BASE wxWindow;
 314
 315 typedef wxWeakRef<wxEvtHandler>  wxEvtHandlerRef;
 316 typedef wxWeakRef<wxWindow>      wxWindowRef;
 317
 318 #endif // _WX_WEAKREF_H_
 319