added a tech note explaining how to write a new XRC handler

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@48141 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/tech/index.txt

@@ -24,6 +24,6 @@ tn0020.txt   Binary compatibility and wxWidgets
 tn0021.txt   How to add a new wxUSE_XXX preprocessor constant
 tn0022.txt   Working with the wxWidgets release system
 tn0023.txt   Adding a new app/screenshot to the wxWidgets.org front page
-
+tn0024.txt   How to add a new XRC handler
 
 Version: $Id$

docs/tech/tn0024.txt

@@ -0,0 +1,55 @@
+                         How to add a new XRC handler
+                         ============================
+
+0. Purpose
+----------
+
+This note describes what needs to be done to add a new XRC handler, i.e. add
+support for loading the objects of some class wxFoo from XRC.
+
+
+1. Implement the handler
+------------------------
+
+By convention, the XRC handler for a class wxFoo declared in wx/foo.h is called
+wxFooXmlHandler and is declared in the file wx/xrc/xh_foo.h (this last rule
+wasn't always respected in the past, however it's not a reason to not respect
+it in the future). The steps for adding a new handler are:
+
+a) Add handler declaration in include/wx/xrc/xh_foo.h, it will usually be the
+   same as in the other files so you can get inspiration for your brand new
+   handler from e.g. wx/xrc/xh_srchctrl.h. Notice the use of wxUSE_FOO if wxFoo
+   is guarded by this symbol.
+
+b) Add implementation in src/xrc/xh_foo.cpp: again, it will be almost always
+   very similar to the existing controls. You will need to add support for
+   the control-specific styles.
+
+
+2. Update the other files
+-------------------------
+
+There are a few other files to update to make wxWidgets aware of the new
+handler:
+
+a) Add the new files created above to build/bakefiles/files.bkl: search for
+   "xh_srchctrl" to see where you need to add them
+
+b) Add #include "wx/xrc/xh_foo.h" to wx/xrc/xh_all.h.
+
+c) Register the new handler in wxXmlResource::InitAllHandlers() in
+   src/xrc/xmlrsall.cpp
+
+
+3. Update the sample
+--------------------
+
+Demonstrate that the new handler works by adding a control using it to
+samples/xrc/rc/controls.xrc.
+
+
+=== EOF ===
+
+Author:  VZ
+Version: $Id: tn0021.txt 47865 2007-08-03 20:00:32Z VZ $
+