Gili wrote:
I also found the existing documentation confusing because it said they
may have either a default constructor or a PageParameters one and I
was left asking... "but why?! What's the difference between the two
constructors? when is each called?" We should just simplify it into a
single constructor.
NO! Like Johan said: it depends on the usecase. Both have meaning. Both
have a right to exist. I am not a native English speaker, and I don't
find it in any way confusing when the documentation states 'either this
or that'. I find it pretty clear when one constructor has PageParameters
and the other doesn't, that /the/ difference is, that one of the
constructors actually wants page parameters, and the other doesn't or
doesn't care. Usually I don't even put a PageParameters constructor in
my pages, but I can definetely see valid usecases for them.
I think it is also clear that a page with either a parameterless
constructor or a PageParameters constructor is bookmarkable. No specific
state is necessary to create such a page. But being bookmarkable is not
special. /NOT/ being bookmarkable is the special case: then you provide
your own parameters to the constructor, which makes them stateful, and
thus not bookmarkable. Very clear distinction in my opinion.
A page can even have both stateful and stateless constructors. Then the
page is both bookmarkable and non-bookmarkable:
public class PersonPage extends WebPage {
public PersonPage(final Person person) {
}
public PersonPage(final PageParameters parameters) {
}
public PersonPage() {
}
}
One page, multiple constructors. Wicket can only cope with the default
and PageParameters constructor, as those are only known to Wicket and
are constructable from a HttpRequest (with or without parameters). The
Person based constructor is specific for your application. So you can
use it all over your application in Links, submits, etc. But you can't
use a page constructed using the Person constructor in a bookmark as
there is no way to construct the required person object.
And what happens if you only have a default constructor and the page
needs to be constructed due to an incoming request? The page will be
created, and the request parameters ignored. Just as with any other
servlet/java solution not specifically checking whether a parameter is
extraeneous.
See:
http://www.wicket-library.com/wicket-examples/helloworld?thisParameterDoesntExist=fooBar
Martijn
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