include/wx/tracker.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        wx/tracker.h
   3 // Purpose:     Support class for object lifetime tracking (wxWeakRef<T>)
   4 // Author:      Arne Steinarson
   5 // Created:     2007-12-28
   6 // RCS-ID:      $Id:$
   7 // Copyright:   (c) 2007 Arne Steinarson
   8 // Licence:     wxWindows licence
   9 /////////////////////////////////////////////////////////////////////////////
  10
  11 #ifndef _WX_TRACKER_H_
  12 #define _WX_TRACKER_H_
  13
  14 // This structure represents an object tracker and is stored in a linked list
  15 // in the tracked object. It is only used in one of its derived forms.
  16 struct wxTrackerNode
  17 {
  18     wxTrackerNode() : m_next(NULL) { }
  19     virtual ~wxTrackerNode() { }
  20
  21     virtual void OnObjectDestroy() = 0;
  22
  23     // This is to tell the difference between different tracker node types.
  24     // It's a replacement of dynamic_cast<> for this class since dynamic_cast
  25     // may be disabled (and we don't have wxDynamicCast since wxTrackerNode
  26     // is not derived wxObject).
  27     enum wxTrackerNodeType { WeakRef, EventConnectionRef };
  28
  29     virtual wxTrackerNodeType GetType() = 0;
  30
  31 protected:
  32     wxTrackerNode *m_next;
  33
  34     friend class wxTrackableBase;    // For list access
  35     friend class wxEvtHandler;       // For list access
  36 };
  37
  38
  39 // Add-on base class for a trackable object.
  40 struct wxTrackableBase
  41 {
  42     wxTrackableBase() : m_first(NULL) { }
  43
  44     ~wxTrackableBase()
  45     {
  46         // Notify all registered refs
  47
  48         // OnObjectDestroy has to remove the item from the link chain
  49         while ( m_first )
  50         {
  51             wxTrackerNode *first = m_first;
  52             first->OnObjectDestroy();
  53             RemoveNode(first);
  54         }
  55     }
  56
  57     void AddNode(wxTrackerNode *node)
  58     {
  59         node->m_next = m_first;
  60         m_first = node;
  61     }
  62
  63     void RemoveNode(wxTrackerNode *node)
  64     {
  65         for ( wxTrackerNode **pn = &m_first; *pn; pn = &(*pn)->m_next )
  66         {
  67             if ( *pn == node )
  68             {
  69                 *pn = node->m_next;
  70                 return;
  71             }
  72         }
  73
  74         wxFAIL_MSG( "node should be present" );
  75     }
  76
  77     wxTrackerNode *GetFirst() { return m_first; }
  78
  79 protected:
  80     wxTrackerNode *m_first;
  81 };
  82
  83 // The difference to wxTrackableBase is that this class adds
  84 // a VTable to enable dynamic_cast query for wxTrackable.
  85 struct wxTrackable : wxTrackableBase
  86 {
  87     virtual ~wxTrackable() { }
  88 };
  89
  90
  91 // Helper to decide if an object has a base class or not
  92 // (strictly speaking, this test succeeds if a type is convertible
  93 //  to another type in some way.)
  94 template <class T, class B>
  95 struct wxHasBase
  96 {
  97         static char Match(B *pb);
  98         static int Match(...);
  99
 100         enum { value = sizeof(Match((T*)NULL)) == sizeof(char) };
 101 };
 102
 103 // A structure to cast to wxTrackableBase, using either static_cast<> or
 104 // dynamic_cast<>.
 105 template <class T, bool is_static>
 106 struct wxTrackableCaster;
 107
 108 template <class T>
 109 struct wxTrackableCaster<T, true>
 110 {
 111     static wxTrackableBase* Cast(T* pt)
 112     {
 113         return static_cast<wxTrackableBase *>(pt);
 114     }
 115 };
 116
 117 #ifdef HAVE_DYNAMIC_CAST
 118
 119 template <class T>
 120 struct wxTrackableCaster<T, false>
 121 {
 122     static wxTrackableBase *Cast(T* pt)
 123     {
 124         return dynamic_cast<wxTrackableBase *>(pt);
 125     }
 126 };
 127
 128 #else // !HAVE_DYNAMIC_CAST
 129
 130 template <class T>
 131 struct wxTrackableCaster<T, false>
 132 {
 133     static wxTrackableBase *Cast(T* pt) { return NULL; }
 134 };
 135
 136 #endif // HAVE_DYNAMIC_CAST/!HAVE_DYNAMIC_CAST
 137
 138 #endif // _WX_TRACKER_H_
 139