> Wicket (just like Java) does not support multiple inheritance. If
you're
> creating a base page that has two blocks that need to be filled in,
you
> can:
I agree that wicket shouldn't support multiple inheritance but I'm not
sure that what is required here is multiple inheritance.
In the wicket parallel universe multiple inheritance would be
represented by one page extending from multiple base pages but that's
not what is required here and that would indeed be a bad path to trod.
What I have had the need for many times is for a base page to have
multiple overridable 'sections' - one base page but multiple sections
within that page that could be overridden (or not) by pages that extend
that page. This does not represent multiple inheritance. It is the
equivalent of Java allowing multiple overridable methods in a single
base class. In Java classes that extend the base class can override one
or more of the virtual (non final) methods in the base class but the
same rule applies - any class/page can only extend a single base
class/page.
The constraint that wicket has now is that only one section of a page
can be overridden by the 'limit of one' child/extend wicket tags. As
only one overridable section is currently allowed in wicket there is no
need to identify it. If wicket were to allow multiple sections in a base
page to be overridden in derived pages then a simple identification
scheme would be required - much like Java uses method signatures to
identify the methods that are being overridden.
Eg.,
BasePage.html:
<body>
<div id="container">
<wicket:section id="header">
<!-- markup will be used if no derived page overrides it
--.
<h1>my website</h1.
</wicket:section>
<hr />
<wicket:section id="body">
<!-- a derived page should override this -->
</wicket;section>
<hr />
<!-- footer same for every page - no overriding -->
<div class="footer">
<p>copyright 2010 acme corp</p>
</div>
</div>
</body>
WelcomePage.html:
<body>
<!-- happy to use base page's header so no header section
override -->
<wicket:section id="body">
<h1>Welcome to my website!</h1>
My website is the best because it uses wicket!
</wicket:section>
</body>
Note how I've used the same tag 'section' in both base and extended
pages to avoid the obvious issue that occurs should someone extend the
WelcomePage.html above. Ie. When inheritance is chained over more than
two levels. In that case it becomes very wrong to specify whether a
section is 'overriding' (extend) or can be overridden (child). Much like
in Java inheritance you don't specify each method as being a 'child' or
'extension'. Instead, the mere presence of a method with identical
signature as in a base class indicates that that method is overriding
the base class method. That would seem an obvious model for overridable
markup sections in wicket also.
This idea/issue has been raised a few times before in this list and once
a remarkably small patch was even developed that would enable this to
work.
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