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     // test for pointer validity: defining conversion to unspecified_bool_type
  29     // and not more obvious bool to avoid implicit conversions to integer types
  30     typedef T *(wxWeakRef<T>::*unspecified_bool_type)() const;
  31     operator unspecified_bool_type() const
  32     {
  33         return m_pobj ? &wxWeakRef<T>::get : NULL;
  34     }
  35
  36     T * get() const
  37     {
  38         return m_pobj;
  39     }
  40
  41     T* operator->()
  42     {
  43         wxASSERT(m_pobj != NULL);
  44         return m_pobj;
  45     }
  46
  47     T& operator*() const
  48     {
  49         wxASSERT(m_pobj != NULL);
  50         return *m_pobj;
  51     }
  52
  53     T* operator=(T *pobj)
  54     {
  55         Assign(pobj);
  56         return m_pobj;
  57     }
  58
  59     // Assign from another weak ref, point to same object
  60     T* operator = (const wxWeakRef<T> &wr)
  61     {
  62         Assign(wr);
  63         return m_pobj;
  64     }
  65
  66     virtual void OnObjectDestroy()
  67     {
  68         // Tracked object itself removes us from list of trackers
  69         wxASSERT( m_pobj );
  70         m_pobj = NULL;
  71     }
  72
  73 protected:
  74     friend class wxTrackableBase;
  75     friend class wxEvtHandler;
  76
  77     virtual wxTrackerNodeType GetType() { return WeakRef; }
  78
  79     void Assign(T* pobj)
  80     {
  81         if ( m_pobj == pobj )
  82             return;
  83
  84         // First release old object if any
  85         if ( m_pobj )
  86         {
  87             // Remove ourselves from object tracker list
  88             // This does static_cast if available, otherwise it tries dynamic cast
  89             wxTrackableBase *pt = wxTrackableCaster<T,wxHasBase<T,wxTrackableBase>::value >::Cast(m_pobj);
  90             wxASSERT(pt);
  91             pt->RemoveNode(this);
  92             m_pobj = NULL;
  93         }
  94
  95         // Now set new trackable object
  96         if ( pobj )
  97         {
  98             wxTrackableBase *pt = wxTrackableCaster<T,wxHasBase<T,wxTrackableBase>::value >::Cast(pobj);
  99             if( pt )
 100             {
 101                 pt->AddNode( this );
 102                 m_pobj = pobj;
 103             }
 104             else
 105             {
 106                 // If the tracked we want to track does not support wxTackableBase, then
 107                 // log a message and keep the NULL object pointer.
 108                 wxLogWarning( _T("wxWeakRef::Assign - Type does not provide wxTrackableBase - resetting tracked object") );
 109             }
 110         }
 111     }
 112
 113     T *m_pobj;
 114 };
 115
 116 // Provide some basic types of weak references
 117 class WXDLLIMPEXP_FWD_BASE wxObject;
 118 class WXDLLIMPEXP_FWD_BASE wxEvtHandler;
 119 class WXDLLIMPEXP_FWD_CORE wxWindow;
 120
 121 typedef wxWeakRef<wxObject>      wxObjectRef;
 122 typedef wxWeakRef<wxEvtHandler>  wxEvtHandlerRef;
 123 typedef wxWeakRef<wxWindow>      wxWindowRef;
 124
 125 #endif // _WX_WEAKREF_H_
 126