On Oct 1, 2009, at 05:49, Paul Bruneau wrote:
I got no responses to my query, which probably means I asked
something poorly, but I needed to write another NSValueTransformer
for my project (to convert dollars into pennies and back) and I saw
the same behavior so I thought I'd ask again.
To summarize: When I use my NSValueTransformers in a cell of an
NSTableView, the entered value gets transformed twice--once going in
to my model, then it comes back out to the view--which is good
because it cleans up the entered value and makes it be optimal (as
outlined in my original question below).
But when I use the transformer on a regular NSTextField, I don't get
that benefit. It properly transforms the value and the correct value
gets stored in my model, but the reverse transformation doesn't fire
like it does when used in the table view.
I *suspect* the answer is that there's no particular guarantee (in the
sense of no API contract) that the reverse transformation will be run
at any point as a result of editing the text. It's easy to see why it
would happen in the table view case, simply because the cell must be
redrawn (because of the removal of the field editor text field) at the
end of editing.
So, if your general intent is to prettify the text string entered by
the user, then you should use the appropriate mechanism to ensure that
-- validation. Write a validate<Key> method for the underlying
property, and modify the ioValue parameter before returning YES. This
should get your freestanding text fields formatted properly when a
regular text field is edited. (Within this method, you'd run your
value transformer in reverse, of course.)
A NSFormatter is another way to go, but it seems like a lot more
trouble for behavior that validate<Key> is designed to provide easily.
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