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
  78 #if !defined(HAVE_PARTIAL_SPECIALIZATION) || !defined(HAVE_TEMPLATE_OVERLOAD_RESOLUTION)
  79     #define USE_STATIC_WEAKREF
  80 #endif
  81
  82
  83 #ifndef USE_STATIC_WEAKREF
  84 template<class T,bool use_static>
  85 struct wxWeakRefImpl;
  86
  87 // Intermediate class, to select the static case above.
  88 template <class T>
  89 struct wxWeakRefImpl<T, true> : public wxWeakRefStatic<T>
  90 {
  91     enum { value = 1 };
  92 };
  93
  94 // Weak ref implementation when T does not have wxTrackable as known base class
  95 template<class T>
  96 struct wxWeakRefImpl<T, false> : public wxTrackerNode
  97 {
  98     void Release()
  99     {
 100         // Release old object if any
 101         if ( m_pobj )
 102         {
 103             // Remove ourselves from object tracker list
 104             m_ptbase->RemoveNode(this);
 105             m_pobj = NULL;
 106             m_ptbase = NULL;
 107         }
 108     }
 109
 110 protected:
 111     wxWeakRefImpl() : m_pobj(NULL), m_ptbase(NULL) { }
 112
 113     // Assign receives most derived class here and can use that
 114     template <class TDerived>
 115     void Assign( TDerived* pobj )
 116     {
 117         AssignHelper( pobj, wxInt2Type<wxIsStaticTrackable<TDerived>::value>() );
 118     }
 119
 120     template <class TDerived>
 121     void AssignHelper(TDerived* pobj, wxInt2Type<true>)
 122     {
 123         wxTrackable *ptbase = static_cast<wxTrackable*>(pobj);
 124         DoAssign( pobj, ptbase );
 125     }
 126
 127 #ifdef HAVE_DYNAMIC_CAST
 128     void AssignHelper(T* pobj, wxInt2Type<false>)
 129     {
 130         // A last way to get a trackable pointer
 131         wxTrackable *ptbase = dynamic_cast<wxTrackable*>(pobj);
 132         if ( ptbase )
 133         {
 134             DoAssign( pobj, ptbase );
 135         }
 136         else
 137         {
 138             wxFAIL_MSG( "Tracked class should inherit from wxTrackable" );
 139
 140             Release();
 141         }
 142     }
 143 #endif // HAVE_DYNAMIC_CAST
 144
 145     void AssignCopy(const wxWeakRefImpl& wr)
 146     {
 147         DoAssign(wr.m_pobj, wr.m_ptbase);
 148     }
 149
 150     void DoAssign( T* pobj, wxTrackable *ptbase ) {
 151         if( m_pobj==pobj ) return;
 152         Release();
 153
 154         // Now set new trackable object
 155         if( pobj )
 156         {
 157             // Add ourselves to object tracker list
 158             wxASSERT( ptbase );
 159             ptbase->AddNode( this );
 160             m_pobj = pobj;
 161             m_ptbase = ptbase;
 162         }
 163     }
 164
 165     virtual void OnObjectDestroy()
 166     {
 167         // Tracked object itself removes us from list of trackers
 168         wxASSERT( m_pobj!=NULL );
 169         m_pobj = NULL;
 170         m_ptbase = NULL;
 171     }
 172
 173     T *m_pobj;
 174     wxTrackable *m_ptbase;
 175 };
 176
 177 #endif // #ifndef USE_STATIC_WEAKREF
 178
 179
 180
 181 // A weak reference to an object of type T, where T has type wxTrackable
 182 // (usually statically but if not dynamic_cast<> is tried).
 183 template <class T>
 184 class wxWeakRef : public
 185 #ifdef USE_STATIC_WEAKREF
 186                   wxWeakRefStatic<T>
 187 #else
 188                   wxWeakRefImpl<T, wxIsStaticTrackable<T>::value>
 189 #endif
 190 {
 191 public:
 192     // Default ctor
 193     wxWeakRef() { }
 194
 195     // When we have the full type here, static_cast<> will always work
 196     // (or give a straight compiler error).
 197     template <class TDerived>
 198     wxWeakRef(TDerived* pobj)
 199     {
 200         Assign(pobj);
 201     }
 202
 203     template <class TDerived>
 204     wxWeakRef<T>& operator=(TDerived* pobj)
 205     {
 206         Assign(pobj);
 207         return *this;
 208     }
 209
 210     wxWeakRef<T>& operator=(const wxWeakRef<T>& wr)
 211     {
 212         AssignCopy(wr);
 213         return *this;
 214     }
 215
 216     virtual ~wxWeakRef() { this->Release(); }
 217
 218     // Smart pointer functions
 219     T& operator*() const { return *this->m_pobj; }
 220     T* operator->() const { return this->m_pobj; }
 221
 222     T* get() const { return this->m_pobj; }
 223     operator T*() const { return get(); }
 224 };
 225
 226
 227 // Weak ref implementation assign objects are queried for wxTrackable
 228 // using dynamic_cast<>
 229 template <class T>
 230 class wxWeakRefDynamic : public wxTrackerNode
 231 {
 232 public:
 233     wxWeakRefDynamic() : m_pobj(NULL) { }
 234
 235     wxWeakRefDynamic(T* pobj) : m_pobj(pobj)
 236     {
 237         Assign(pobj);
 238     }
 239
 240     virtual ~wxWeakRefDynamic() { Release(); }
 241
 242     // Smart pointer functions
 243     T& operator * (){ wxASSERT(this->m_pobj); return *m_pobj; }
 244     T* operator -> (){ wxASSERT(this->m_pobj); return m_pobj; }
 245     T* operator = (T* pobj) { Assign(pobj); return m_pobj; }
 246
 247     T* get(){ return this->m_pobj; }
 248
 249     // operator T* (){ return this->m_pobj; }
 250
 251     // test for pointer validity: defining conversion to unspecified_bool_type
 252     // and not more obvious bool to avoid implicit conversions to integer types
 253     typedef T *(wxWeakRef<T>::*unspecified_bool_type)() const;
 254     operator unspecified_bool_type() const
 255     {
 256         return m_pobj ? &wxWeakRef<T>::get : NULL;
 257     }
 258
 259     // Assign from another weak ref, point to same object
 260     T* operator = (const wxWeakRef<T> &wr) { Assign( wr.get() ); return this->m_pobj; }
 261
 262     void Release()
 263     {
 264         // Release old object if any
 265         if( m_pobj )
 266         {
 267             // Remove ourselves from object tracker list
 268             wxTrackable *pt = dynamic_cast<wxTrackable*>(m_pobj);
 269             wxASSERT(pt);
 270             pt->RemoveNode(this);
 271             m_pobj = NULL;
 272         }
 273     }
 274
 275 protected:
 276     void Assign(T *pobj)
 277     {
 278         if ( m_pobj == pobj )
 279             return;
 280
 281         Release();
 282
 283         // Now set new trackable object
 284         if ( pobj )
 285         {
 286             // Add ourselves to object tracker list
 287             wxTrackable *pt = dynamic_cast<wxTrackable*>(pobj);
 288             if ( pt )
 289             {
 290                 pt->AddNode(this);
 291                 m_pobj = pobj;
 292             }
 293             else
 294             {
 295                 // If the object we want to track does not support wxTackable, then
 296                 // log a message and keep the NULL object pointer.
 297                 wxFAIL_MSG( "Tracked class should inherit from wxTrackable" );
 298             }
 299         }
 300     }
 301
 302     virtual void OnObjectDestroy()
 303     {
 304         wxASSERT_MSG( m_pobj, "tracked object should have removed us itself" );
 305
 306         m_pobj = NULL;
 307     }
 308
 309     T *m_pobj;
 310 };
 311
 312 // Provide some basic types of weak references
 313 class WXDLLIMPEXP_FWD_BASE wxEvtHandler;
 314 class WXDLLIMPEXP_FWD_CORE wxWindow;
 315
 316 typedef wxWeakRef<wxEvtHandler>  wxEvtHandlerRef;
 317 typedef wxWeakRef<wxWindow>      wxWindowRef;
 318
 319 #endif // _WX_WEAKREF_H_
 320