Hi Quincey,
Thank you very much for taking the time to reply and help me out.
These diagrams are *very* old (2003, it looks like), and it's not
clear if they're accurate any more. So anything deduced from them
needs to be verified. However, they don't give you any good news,
because they suggest that NSFormatter validation occurs before KVC
validation, which isn't what you said you wanted at all.
Aside from that, note that KVC validation doesn't happen when you
expect unless you check "validates immediately" in the bindings
options. You didn't say whether or not you did this.
I do have the "validates immediately" option checkmarked in IB.
It's actually okay if formatter validation is triggered before the KVC
validation, so long as the latter happens at some point. I can simply
have no min/max set for my formatter, so that validation always passes.
Unfortunately this doesn't help with my ultimate goal of validating
values bound to NSUserDefaults.
Regarding NSUserDefaults, I don't see anything in the documentation
that claims KVC compliance for NSUserDefaults, though I could easily
have missed it. Specifically, valueForKey: and setValue:forKey: are
not part of NSUserDefaults' publicly documented API. The fact that
you can bind to NSUserDefaults suggests that it is KVC compliant but
the compliance may only be partial and not include validation.
Fair enough.
TBH, adding a category to NSUserDefaults for this purpose seems kind
of hacky, solely for the convenience of binding directly to
NSUserDefaults in IB.
I don't feel like having categories on NSUserDefaults to add specific
validator methods is a hack. It seems like a great way to enforce the
constraint in the model (ie: the defaults are the model). If
NSUserDefaults wasn't designed for this, then sure, it's not a good
idea. But considering that Apple provides a shared controller
specifically for binding to the user defaults in IB, I wish they had
thought of validation too.
The alternative is to bind your user interface to properties of
(say) your application delegate that provide the validation you
want, along with custom getters and setters. These properties would
use NSUserDefaults as their "backing store".
That sounds like more glue code than with manual target/action/update
code.
I think at this point my best option will be to subclass
NSNumberFormatter and override the value extraction methods so that
numbers outside the min/max are silently clipped before Apple has a
chance to see them.
Thanks again for your help!
Best,
~Martin
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