interface/wx/weakref.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        weakref.h
   3 // Purpose:     interface of wxWeakRefDynamic<T>, wxWeakRef<T>
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9
  10 /**
  11     @class wxWeakRefDynamic<T>
  12
  13     wxWeakRefDynamic<T> is a template class for weak references that is used in
  14     the same way as wxWeakRef<T>. The only difference is that wxWeakRefDynamic
  15     defaults to using @c dynamic_cast for establishing the object reference
  16     (while wxWeakRef defaults to @c static_cast).
  17
  18     So, wxWeakRef will detect a type mismatch during compile time and will
  19     have a little better run-time performance. The role of wxWeakRefDynamic
  20     is to handle objects which derived type one does not know.
  21
  22     @note wxWeakRef<T> selects an implementation based on the static type of T.
  23           If T does not have wxTrackable statically, it defaults to to a mixed-
  24           mode operation, where it uses @c dynamic_cast as the last measure
  25           (if available from the compiler and enabled when building wxWidgets).
  26
  27     For general cases, wxWeakRef<T> is the better choice.
  28
  29     For API documentation, see: wxWeakRef<T>.
  30
  31     @nolibrary
  32     @category{misc}
  33 */
  34 template<typename T>
  35 class wxWeakRefDynamic<T>
  36 {
  37 public:
  38
  39 };
  40
  41
  42
  43 /**
  44     @class wxWeakRef<T>
  45
  46     wxWeakRef<T> is a template class for weak references to wxWidgets objects,
  47     such as wxEvtHandler, wxWindow and wxObject.
  48     A weak reference behaves much like an ordinary pointer, but when the object
  49     pointed is destroyed, the weak reference is automatically reset to a @NULL pointer.
  50
  51     wxWeakRef<T> can be used whenever one must keep a pointer to an object
  52     that one does not directly own, and that may be destroyed before the object
  53     holding the reference.
  54
  55     wxWeakRef<T> is a small object and the mechanism behind it is fast
  56     (@b O(1)). So the overall cost of using it is small.
  57
  58     Example:
  59
  60     @code
  61     wxWindow *wnd = new wxWindow( parent, wxID_ANY, "wxWindow" );
  62     wxWeakRef<wxWindow> wr = wnd;
  63     wxWindowRef wr2 = wnd;        // Same as above, but using a typedef
  64     // Do things with window
  65     wnd->Show( true );
  66     // Weak ref is used like an ordinary pointer
  67     wr->Show( false );
  68     wnd->Destroy();
  69     // Now the weak ref has been reset, so we don't risk accessing
  70     // a dangling pointer:
  71     wxASSERT( wr==NULL );
  72     @endcode
  73
  74     wxWeakRef<T> works for any objects that are derived from wxTrackable.
  75     By default, wxEvtHandler and wxWindow derive from wxTrackable.
  76     However, wxObject does not, so types like wxFont and wxColour are not
  77     trackable. The example below shows how to create a wxObject derived class
  78     that is trackable:
  79
  80     @code
  81     class wxMyTrackableObject : public wxObject, public wxTrackable
  82     {
  83         // ... other members here
  84     };
  85     @endcode
  86
  87     The following types of weak references are predefined:
  88
  89     @code
  90     typedef wxWeakRef<wxEvtHandler>  wxEvtHandlerRef;
  91     typedef wxWeakRef<wxWindow>      wxWindowRef;
  92     @endcode
  93
  94     @nolibrary
  95     @category{misc}
  96
  97     @see wxSharedPtr<T>, wxScopedPtr<T>
  98 */
  99 template<typename T>
 100 class wxWeakRef<T> : public wxTrackerNode
 101 {
 102 public:
 103     /**
 104         Constructor. The weak reference is initialized to @e pobj.
 105     */
 106     wxWeakRef(T* pobj = NULL);
 107
 108     /**
 109         Copy constructor.
 110     */
 111     wxWeakRef(const wxWeakRef<T>& wr);
 112
 113     /**
 114         Destructor.
 115     */
 116     ~wxWeakRef();
 117
 118     /**
 119         Called when the tracked object is destroyed. Be default sets
 120         internal pointer to @NULL.
 121         You need to call this method if you override it.
 122     */
 123     virtual void OnObjectDestroy();
 124
 125     /**
 126         Release currently tracked object and rests object reference.
 127     */
 128     void Release();
 129
 130     /**
 131         Returns pointer to the tracked object or @NULL.
 132     */
 133     T* get() const;
 134
 135     /**
 136         Release currently tracked object and start tracking the same object as
 137         the wxWeakRef @e wr.
 138     */
 139     T* operator =(wxWeakRef<T>& wr);
 140
 141     /**
 142         Implicit conversion to T*.
 143         Returns pointer to the tracked object or @NULL.
 144     */
 145     T* operator*() const;
 146
 147     /**
 148         Returns a reference to the tracked object.
 149         If the internal pointer is @NULL this method will cause an assert in debug mode.
 150     */
 151     T& operator*() const;
 152
 153     /**
 154         Smart pointer member access.
 155         Returns a pointer to the tracked object.
 156         If the internal pointer is @NULL this method will cause an assert in debug mode.
 157     */
 158     T* operator-();
 159
 160     /**
 161         Releases the currently tracked object and starts tracking @e pobj.
 162         A weak reference may be reset by passing @e @NULL as @e pobj.
 163     */
 164     T* operator=(T* pobj);
 165 };
 166