Hi Ken,
somethings I get the feeling you use this mailinglist like a chat system
providing much info in many many small chunks. Can't you just gather all
information first and afterwards throw it to the mailinglist? And for
this particular topic, I miss the stacktrace maybe I did not see it. Can
you show the complete NPE stacktrace? And how is "property binding"
related to your NPE?
When looking at CollectionGridDataSource.java I see:
public CollectionGridDataSource(final Collection collection)
{
assert collection != null;
list = CollectionFactory.newList(collection);
}
so the ctor is guarded by an assert. When you pass "-ea" as VM argument
(enable asserts) you will get an assertion error. So honestly I do not
believe "null" is an acceptable value and the NPE occurs later on in the
CTOR of ArrayList. Maybe I will be corrected but due to Tapestry magic
you get some kind of a default GridDataSource when your method does not
provide one, therfore the null check works in your particular case. If
you do not want to rely on T5 magic I prefer generally to make hidden
things obvious so why not simply writing:
return new CollectionGridDataSource(null != collection ? collection
: Collections.EMPTY_LIST)
And when you "hate null checks" you can modify your collection creation
code to explicitly return a empty collection in case it's null. This
does not prevent you from the check in general, but this "null check
code" moves deeper into the service layer of your app which is good
anyway and you never have to think about this kind of NPE in your
client, because you know "null collection" will never returned. That's
the way I treat it, too. Either you spread null checks or you create
empty collections. For the latter do it at the source and don't let the
'null' escape....
Jens
Am 29.05.13 02:36, schrieb Ken in Nashua:
alright... i hate doing null checks...
because if you get into the habit of it...
you never know if your actually writing a legit piece of code
So I did it anyway
public GridDataSource getSource() {
if (collection != null )
return new CollectionGridDataSource(collection);
else return null;
}
and it works..
my form comes up... initialized..
table is empty.. as expected with the nice message "No objects to render
But is my code legit?
"
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