This issue has come up many, many times before: http://www.mail-archive.com/users@wicket.apache.org/msg06381.html http://www.mail-archive.com/wicket-u...@lists.sourceforge.net/msg26247.h tml
Unfortunately some people try to convince the group that proposals like the one you have presented here are not in line with Java's 'single inheritance' model and therefore must be 'multiple inheritance' but they are clearly not understanding the issue properly. What you are suggesting here is not 'the horror of multiple inheritance'. It is simply single inheritance with 'multiple overridable markup sections' and therefore would IMHO be an excellent enhancement to Wicket. Stefan and I were discussing multiple options more than a year ago and Stefan even went to the effort of creating a Wicket patch that implemented support for overriding multiple sections but I'm pretty sure it hasn't yet been added to SVN. Stefan raised a feature request for this in JIRA: https://issues.apache.org/jira/browse/WICKET-1134 The only thing extra that we discussed that you have not included in your sample is that when we move from ONE overridable markup section to MULTIPLE overridable sections (but still only a single super class/markup!) we need to introduce and a way of identifying each section (which obviously isn't required when you limit the number of overridable sections to 1. The great thing about identifying which section you are overriding is that you can pick and choose which sections you override and which you just 'default' to the markup of the super class/markup file. I'm actually thinking that using specific <wicket:extend> and <wicket:child> is a big hinderance to chaining in a hierarchy because you have a different tag depending on whether you are providing a 'markup section' to be overridden or whether you are overriding a 'markup section'. This gets awkward and clumsy when it comes to flexible 'chaining' down an inheritance hierarchy and Java has no such equivalent. We could probably have a single tag to be used consistently in super or subclass to allow very simple syntax that supports fluid inheritance down a markup hierarchy: <wicket:namedsection id="header"> (or whatever) Overriding is then optional: absence of a named section in a subclass markup simply means that the markup from the closest superclass markup should be used. I really hope this gets implemented soon. The 'workaround' that is often suggested is a 'component based' workaround rather than a truly object oriented approach that allows multiple sections to be overridden. As a hard line OOer that doesn't quite cut it. I have even gone to the extent of creating a special markup preparser that lets me write markup with multiple overridable sections which are then compiled to 'flattened' markup for Wicket to process at run time. It works extremely well and satisfies my needs but it would be nicer if it was supported natively in Wicket. >-----Original Message----- >From: Arjun Dhar [mailto:dhar...@yahoo.com] >Sent: Monday, 5 July 2010 3:40 PM >To: users@wicket.apache.org >Subject: Single inheritence in parts > > >Hi, > all the examples etc suggest that Single inheritence is possible but I >cant >break it up. The break up is essential when you want to merge common parts >of your MARKUP with multiple specific parts of the Child page. > >Example: > > ><HTML> ><HEAD><title>BASE TEMPLATE / PARENT PAGE</title></HEAD> > ><BODY> > <wicket:child /> > <br /> > <h2>Some other Html common</h2> > <wicket:child /> ></BODY> ></HTML> > > >------------------------------------------- > ><HTML> ><HEAD><title>CHILD PAGE 1</title></HEAD> > ><BODY> > <wicket:extend> > Part 1 specific to Child Page > </wicket:extend> > Any HTML here can be ignored as conceptually anyway what appears in ><extend> is what should be rendered from a child page. > <wicket:extend> > Part 2 Specific to Child Page (will appear after common >HTML in parent page) > </wicket:extend> ></BODY> ></HTML> > > >I tried this, only the first part renders. I'm wondering if we can add such >capability. Conceptually I don't see why not. If already possible do let me >know or consider as a feature request?! > >-Thanks Arjun >-- >View this message in context: http://apache- >wicket.1842946.n4.nabble.com/Single-inheritence-in-parts- >tp2278064p2278064.html >Sent from the Wicket - User mailing list archive at Nabble.com. > >--------------------------------------------------------------------- >To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org >For additional commands, e-mail: users-h...@wicket.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org For additional commands, e-mail: users-h...@wicket.apache.org
