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Run time class information overview

Classes: wxObject, 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 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 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.

wxClassInfo
Example


wxClassInfo

Run time class information overview

Class: 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:

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 wxObject and wxCreateDynamicObject.


Example

In a header file wx_frame.h:

class wxFrame: public wxWindow
{
  DECLARE_DYNAMIC_CLASS(wxFrame)

 private:
  char *frameTitle;
 public:
  ...
};
In a C++ file wx_frame.cc:

IMPLEMENT_DYNAMIC_CLASS(wxFrame, wxWindow)

wxFrame::wxFrame(void)
{
...
}