docs/latex/wx/truntime.tex

   1 \section{Run time class information overview}\label{runtimeclassoverview}
   2
   3 Classes: \helpref{wxObject}{wxobject}, \helpref{wxClassInfo}{wxclassinfo}.
   4
   5 One of the failings of C++ is that no run-time information is provided
   6 about a class and its position in the inheritance hierarchy.
   7 Another is that instances of a class cannot be created just by knowing the name of a class,
   8 which makes facilities such as persistent storage hard to implement.
   9
  10 Most C++ GUI frameworks overcome these limitations by means of a set of
  11 macros and functions and wxWindows (from version 1.62) is no exception.
  12 Each class that you wish to be known the type system should have
  13 a macro such as DECLARE\_DYNAMIC\_CLASS just inside the class declaration.
  14 The macro IMPLEMENT\_DYNAMIC\_CLASS should be in the implementation file.
  15
  16 Variations on these \helpref{macros}{macros} are used for multiple inheritance, and abstract
  17 classes that cannot be instantiated dynamically or otherwise.
  18
  19 DECLARE\_DYNAMIC\_CLASS inserts a static wxClassInfo declaration into the
  20 class, initialized by IMPLEMENT\_DYNAMIC\_CLASS. When initialized, the
  21 wxClassInfo object inserts itself into a linked list (accessed through
  22 wxClassInfo::first and wxClassInfo::next pointers). The linked list
  23 is fully created by the time all global initialisation is done.
  24
  25 IMPLEMENT\_DYNAMIC\_CLASS is a macro that not only initialises the static
  26 wxClassInfo member, but defines a global function capable of creating a
  27 dynamic object of the class in question. A pointer to this function is
  28 stored in wxClassInfo, and is used when an object should be created
  29 dynamically.
  30
  31 wxObject::IsKindOf uses the linked list of wxClassInfo. It takes
  32 a wxClassInfo argument, so use CLASSINFO(className) to return an
  33 appropriate wxClassInfo pointer to use in this function.
  34
  35 The function \helpref{wxCreateDynamicObject}{wxcreatedynamicobject} can be used
  36 to construct a new object of a given type, by supplying a string name.
  37 If you have a pointer to the wxClassInfo object instead, then you
  38 can simply call wxClassInfo::CreateObject.
  39
  40 \subsection{wxClassInfo}\label{wxclassinfooverview}
  41
  42 \overview{Run time class information overview}{runtimeclassoverview}
  43
  44 Class: \helpref{wxClassInfo}{wxclassinfo}
  45
  46 This class stores meta-information about classes. An application
  47 may use macros such as DECLARE\_DYNAMIC\_CLASS and IMPLEMENT\_DYNAMIC\_CLASS
  48 to record run-time information about a class, including:
  49
  50 \begin{itemize}\itemsep=0pt
  51 \item its position in the inheritance hierarchy;
  52 \item the base class name(s) (up to two base classes are permitted);
  53 \item a string representation of the class name;
  54 \item a function that can be called to construct an instance of this class.
  55 \end{itemize}
  56
  57 The DECLARE\_... macros declare a static wxClassInfo variable in a class, which is initialized
  58 by macros of the form IMPLEMENT\_... in the implementation C++ file. Classes whose instances may be
  59 constructed dynamically are given a global constructor function which returns a new object.
  60
  61 You can get the wxClassInfo for a class by using the CLASSINFO macro, e.g. CLASSINFO(wxFrame).
  62 You can get the wxClassInfo for an object using wxObject::GetClassInfo.
  63
  64 See also \helpref{wxObject}{wxobject} and \helpref{wxCreateDynamicObject}{wxcreatedynamicobject}.
  65
  66 \subsection{Example}
  67
  68 In a header file wx\_frame.h:
  69
  70 \begin{verbatim}
  71 class wxFrame: public wxWindow
  72 {
  73   DECLARE_DYNAMIC_CLASS(wxFrame)
  74
  75  private:
  76   char *frameTitle;
  77  public:
  78   ...
  79 };
  80 \end{verbatim}
  81
  82 In a C++ file wx\_frame.cc:
  83
  84 \begin{verbatim}
  85 IMPLEMENT_DYNAMIC_CLASS(wxFrame, wxWindow)
  86
  87 wxFrame::wxFrame(void)
  88 {
  89 ...
  90 }
  91 \end{verbatim}
  92
  93