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.
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.
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) { ... }