include/wx/weakref.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        wx/weakref.h
   3 // Purpose:     wxWeakRef - Generic weak references for wxWidgets
   4 // Author:      Arne Steinarson
   5 // Created:     2007-12-27
   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 // A weak reference to an object of type T, where T has type wxTrackable
  17 // as one of its base classes (in a static or dynamic sense).
  18 template<class T>
  19 class wxWeakRef : public wxTrackerNode
  20 {
  21 public:
  22     typedef T element_type;
  23
  24     wxWeakRef(T *pobj = NULL) : m_pobj(NULL) { Assign(pobj); }
  25
  26     virtual ~wxWeakRef() { Assign(NULL); }
  27
  28     T * get() const
  29     {
  30         return m_pobj;
  31     }
  32
  33     T* operator->()
  34     {
  35         wxASSERT(m_pobj != NULL);
  36         return m_pobj;
  37     }
  38
  39     T& operator*() const
  40     {
  41         wxASSERT(m_pobj != NULL);
  42         return *m_pobj;
  43     }
  44
  45     T* operator=(T *pobj)
  46     {
  47         Assign(pobj);
  48         return m_pobj;
  49     }
  50
  51     // Assign from another weak ref, point to same object
  52     T* operator = (const wxWeakRef<T> &wr)
  53     {
  54         Assign(wr);
  55         return m_pobj;
  56     }
  57
  58     virtual void OnObjectDestroy()
  59     {
  60         // Tracked object itself removes us from list of trackers
  61         wxASSERT( m_pobj );
  62         m_pobj = NULL;
  63     }
  64
  65 protected:
  66     friend class wxTrackableBase;
  67     friend class wxEvtHandler;
  68
  69     virtual wxTrackerNodeType GetType() { return WeakRef; }
  70
  71     void Assign(T* pobj)
  72     {
  73         if ( m_pobj == pobj )
  74             return;
  75
  76         // First release old object if any
  77         if ( m_pobj )
  78         {
  79             // Remove ourselves from object tracker list
  80             // This does static_cast if available, otherwise it tries dynamic cast
  81             wxTrackableBase *pt = wxTrackableCaster<T,wxHasBase<T,wxTrackableBase>::value >::Cast(m_pobj);
  82             wxASSERT(pt);
  83             pt->RemoveNode(this);
  84             m_pobj = NULL;
  85         }
  86
  87         // Now set new trackable object
  88         if ( pobj )
  89         {
  90             wxTrackableBase *pt = wxTrackableCaster<T,wxHasBase<T,wxTrackableBase>::value >::Cast(pobj);
  91             if( pt )
  92             {
  93                 pt->AddNode( this );
  94                 m_pobj = pobj;
  95             }
  96             else
  97             {
  98                 // If the tracked we want to track does not support wxTackableBase, then
  99                 // log a message and keep the NULL object pointer.
 100                 wxLogWarning( _T("wxWeakRef::Assign - Type does not provide wxTrackableBase - resetting tracked object") );
 101             }
 102         }
 103     }
 104
 105     T *m_pobj;
 106 };
 107
 108 // Provide some basic types of weak references
 109 class WXDLLIMPEXP_FWD_BASE wxObject;
 110 class WXDLLIMPEXP_FWD_BASE wxEvtHandler;
 111 class WXDLLIMPEXP_FWD_CORE wxWindow;
 112
 113 typedef wxWeakRef<wxObject>      wxObjectRef;
 114 typedef wxWeakRef<wxEvtHandler>  wxEvtHandlerRef;
 115 typedef wxWeakRef<wxWindow>      wxWindowRef;
 116
 117 #endif // _WX_WEAKREF_H_
 118