On Sep 16, 2010, at 14:00, Martin Wierschin wrote:
> The quick summary:
Actually, you've covered a lot of ground here, so there are multiple issues
implicit in your question.
If you look here:
http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CocoaBindings/Concepts/MessageFlow.html%23//apple_ref/doc/uid/TP40002149-BCICADHC
you'll see the message flow for bindings. In particular, look at figures 2 and
3.
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.
For this much of the problem, you're probably better off configuring the text
field only for KVC validation, and in your validate<Key> method use a local
(created or cached) instance of NSNumberFormatter to convert the text field
string value to a number. (AFAIK it's fine for the input value to be a NSString
and the output value to be a NSNumber.) You would then capture any errors and
incorporate them into the validate<Key> error recovery.
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. Or, it could support the
validateValue:forKey:@"mySpecialValue"error: form of validation without
supporting validateMySpecialValue:error:.
TBH, adding a category to NSUserDefaults for this purpose seems kind of hacky,
solely for the convenience of binding directly to NSUserDefaults in IB. 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".
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