\section{Run time class information overview}\label{runtimeclassoverview}

Classes: \helpref{wxObject}{wxobject}, \helpref{wxClassInfo}{wxclassinfo}.

One of the failings of C++ is that no run-time information is provided
about a class and its position in the inheritance hierarchy.
Another is that instances of a class cannot be created just by knowing the name of a class,
which makes facilities such as persistent storage hard to implement.

Most C++ GUI frameworks overcome these limitations by means of a set of
macros and functions and wxWindows (from version 1.62) is no exception.
Each class that you wish to be known the type system should have
a macro such as DECLARE\_DYNAMIC\_CLASS just inside the class declaration.
The macro IMPLEMENT\_DYNAMIC\_CLASS should be in the implementation file.

Variations on these \helpref{macros}{macros} are used for multiple inheritance, and abstract
classes that cannot be instantiated dynamically or otherwise.

DECLARE\_DYNAMIC\_CLASS inserts a static wxClassInfo declaration into the
class, initialized by IMPLEMENT\_DYNAMIC\_CLASS. When initialized, the
wxClassInfo object inserts itself into a linked list (accessed through
wxClassInfo::first and wxClassInfo::next pointers). The linked list
is fully created by the time all global initialisation is done.

IMPLEMENT\_DYNAMIC\_CLASS is a macro that not only initialises the static
wxClassInfo member, but defines a global function capable of creating a
dynamic object of the class in question. A pointer to this function is
stored in wxClassInfo, and is used when an object should be created
dynamically.

wxObject::IsKindOf uses the linked list of wxClassInfo. It takes
a wxClassInfo argument, so use CLASSINFO(className) to return an
appropriate wxClassInfo pointer to use in this function.

The function \helpref{wxCreateDynamicObject}{wxcreatedynamicobject} can be used
to construct a new object of a given type, by supplying a string name.
If you have a pointer to the wxClassInfo object instead, then you
can simply call wxClassInfo::CreateObject.

\subsection{wxClassInfo}\label{wxclassinfooverview}

\overview{Run time class information overview}{runtimeclassoverview}

Class: \helpref{wxClassInfo}{wxclassinfo}

This class stores meta-information about classes. An application
may use macros such as DECLARE\_DYNAMIC\_CLASS and IMPLEMENT\_DYNAMIC\_CLASS
to record run-time information about a class, including:

\begin{itemize}\itemsep=0pt
\item its position in the inheritance hierarchy;
\item the base class name(s) (up to two base classes are permitted);
\item a string representation of the class name;
\item a function that can be called to construct an instance of this class.
\end{itemize}

The DECLARE\_... macros declare a static wxClassInfo variable in a class, which is initialized
by macros of the form IMPLEMENT\_... in the implementation C++ file. Classes whose instances may be
constructed dynamically are given a global constructor function which returns a new object.

You can get the wxClassInfo for a class by using the CLASSINFO macro, e.g. CLASSINFO(wxFrame).
You can get the wxClassInfo for an object using wxObject::GetClassInfo.

See also \helpref{wxObject}{wxobject} and \helpref{wxCreateDynamicObject}{wxcreatedynamicobject}.

\subsection{Example}

In a header file wx\_frame.h:

\begin{verbatim}
class wxFrame: public wxWindow
{
  DECLARE_DYNAMIC_CLASS(wxFrame)

 private:
  char *frameTitle;
 public:
  ...
};
\end{verbatim}

In a C++ file wx\_frame.cc:

\begin{verbatim}
IMPLEMENT_DYNAMIC_CLASS(wxFrame, wxWindow)

wxFrame::wxFrame(void)
{
...
}
\end{verbatim}


