Hi,
> Jan, please give me a good reason why ListModel is better
> than AbstractList.
> i can only see the downside of needing wrappers everywhere
> for ListModel.
After some thought I think its just fine...java.util.List is a big
interface to implement if you are not using List, but from a wicket
point of view its good/complete/universal
Ignore my last question in my previous mail I think I now understand
ListItem will not have an (public)index anymore (but holds-on to the
model and does a reverse modelobject index lookup to the List if it
wants the index for some reason, to overcome object index changes in the
List between detach and a new attach, correct?)
Jan
>
> thoughts?
>
> jon
>
> Eelco Hillenius wrote:
>
> > So, first the removeAll on each request, and now the ListModel... I
> > argued about these things months ago!
> >
> > Eelco
> >
> > Jonathan Locke wrote:
> >
> >>
> >> this is a good point and i think you're correct. the downside is
> >> that you'll have to wrap all your hibernate Lists in an
> adapter. but
> >> it still sounds good. we should also do this for trees. however,
> >> the implementation you sketched wouldn't be the actual
> implementation
> >> because the whole idea of using indexes is broken. i'd
> like to try
> >> to address all this when i add our first implementation of
> versioning
> >> as described on the list earlier. i hope to get to all of this
> >> before i leave for holland. i had a really satisfactory talk with
> >> chris about versioning and we both think what i sketched
> out on this
> >> list earlier is actually really close to what we need... an
> >> implementation of page versioning as a pluggable strategy.
> in order
> >> for this whole scheme to work though, components like
> ListView /must/
> >> be resilient to changes in the model due to attach/detach. so
> >> indexes cannot work. we have to actually hold onto the
> model that's
> >> in the list in our ListItem implementation... the only downside
> >> there is that you won't be able to use the core listview if you
> >> actually care about indexes... the only case i can think of where
> >> that would matter would be if you had a list with
> duplicate objects
> >> in it. behavior there would be an first or all-or-nothing kind of
> >> thing.
> >>
> >> Jan Blok wrote:
> >>
> >>> Hi,
> >>>
> >>> Is there a reason to use a java.util.List interface in
> the first place?
> >>> Which is quite big to implement for many people, why not define an
> >>> Interface alike javax.swing.ListModel? For example
> >>>
> >>> Public interface IListViewModel
> >>> {
> >>> public Object getObjectAt(int index);
> >>> public int getSize() //more needed?
> >>> }
> >>>
> >>> I think many people have to put there own list objects in a
> >>> (Lazy)ArrayList again...which they do already hold in
> (lazy loading)
> >>> models.
> >>>
> >>> Regards Jan
> >>>
> >>>
> >>>
> >>>
> >>>> -----Original Message-----
> >>>> From: [EMAIL PROTECTED]
> >>>> [mailto:[EMAIL PROTECTED] On Behalf Of
> >>>> Eelco Hillenius
> >>>> Sent: Tuesday, March 08, 2005 8:11 PM
> >>>> To: [email protected]
> >>>> Subject: Re: [Wicket-develop] should we make AbstractResource
> >>>> serializeable or not?
> >>>>
> >>>>
> >>>> We're in the process of reconsidering the ListView
> implementation
> >>>> alltogether I think.
> >>>>
> >>>> If you really want this, you could provide a custom list
> that does
> >>>> this. That list could lazily load it's size: when not
> set yet, you
> >>>> load the actual list (e.g. from a database), but when
> set, return
> >>>> it. And then the actual loading should occur when one of it's
> >>>> accessor methods (like get(int) is called.
> >>>>
> >>>> E.g (haven't tested it, but the idea should work):
> >>>>
> >>>>
> >>>> public class LazyList extends ArrayList
> >>>> {
> >>>> private int size = -1;
> >>>>
> >>>> private boolean loaded = false;
> >>>>
> >>>> public LazyList(List list)
> >>>> {
> >>>> addAll(list);
> >>>> }
> >>>>
> >>>> public int size()
> >>>> {
> >>>> if(size == -1)
> >>>> {
> >>>> load();
> >>>> this.size = super.size();
> >>>> }
> >>>> }
> >>>>
> >>>> public get(int index)
> >>>> {
> >>>> load();
> >>>> return super.get(index);
> >>>> }
> >>>>
> >>>> public void unload()
> >>>> {
> >>>> this.loaded = false;
> >>>> }
> >>>>
> >>>> private void load()
> >>>> {
> >>>> if(!loaded)
> >>>> {
> >>>> this.loaded = true;
> >>>> // do loading here and call super.addAll(..)
> >>>> }
> >>>> }
> >>>>
> >>>> .... etc ....
> >>>>
> >>>>
> >>>> }
> >>>>
> >>>> and your model is like:
> >>>>
> >>>> public class MyModel extends AbstractDetachableModel
> >>>>
> >>>> private LazyList myList; // keep reference to list
> allways; it'll
> >>>> usually be empty
> >>>>
> >>>> protected void onAttach()
> >>>> {
> >>>> if(myList == null)
> >>>> {
> >>>> myList = new LazyList(getSomeList());
> >>>> }
> >>>> }
> >>>>
> >>>> protected void onDetach()
> >>>> {
> >>>> myList.unload();
> >>>> }
> >>>>
> >>>> protected Object onGetObject(Component component)
> >>>> {
> >>>> return myList;
> >>>> }
> >>>>
> >>>> .... etc ....
> >>>>
> >>>>
> >>>>
> >>>> Btw, this might be a usefull pattern to either put on
> the Wiki or
> >>>> in contrib. It's far more efficient for those cases
> where you have
> >>>> a list that doesn't change over requests, are that you want to
> >>>> 'push' the changes in, together with a ListView that
> doesn't remove
> >>>> it's items on each request.
> >>>>
> >>>>
> >>>> Eelco
> >>>>
> >>>>
> >>>>
> >>>>> It just happens that in my case - using a ListView - the
> >>>>
> >>>>
> >>>> list view calls
> >>>>
> >>>>
> >>>>> getModelObject within the onRender method (via getViewSize)
> >>>>
> >>>>
> >>>> this is causing
> >>>>
> >>>>
> >>>>> my detached model to re-attach for every request - even repeated
> >>>>> IredirectListener requests.
> >>>>>
> >>>>> Could this component possibly be changed to remember the
> >>>>
> >>>>
> >>>> size of the list ?
> >>>>
> >>>>
> >>>>> Cameron
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>
> >>>>
> >>>>
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> >>>>
> >>>
> >>>
> >>>
> >>>
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> >>>
> >>
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