Re: [iPhone] Why can't a UITextField be its own delegate?
Re: [iPhone] Why can't a UITextField be its own delegate?
- Subject: Re: [iPhone] Why can't a UITextField be its own delegate?
- From: "Adam R. Maxwell" <email@hidden>
- Date: Sat, 25 Jul 2009 15:41:36 -0700
On Jul 25, 2009, at 3:23 PM, Kyle Sluder wrote:
Internally, UITextField is going to use self.delegate to get its
delegate, following the correct accessor behavior. You've gone and
replaced -delegate to return self. But the delegate pattern says that
messages which this object does not understand should be forwarded to
the delegate. This means that a class with a delegate needs to
implement -respondsToSelector: this way:
- (BOOL)respondsToSelector:(SEL)aSelector {
return [super respondsToSelector:aSelector]
|| [self.delegate respondsToSelector:aSelector];
}
Where is this guaranteed by the delegate pattern? I've created a fair
number of classes with delegates and never done this; it would be
interesting to know that I've been doing it wrong for years ;).
Since -delegate is going to return self, -respondsToSelector: is going
to result in infinite recursion.
So It's Never Safe To Make An Object Its Own Delegate.
Even if it's safe, it's a bizarre way to do something, especially if
you're already subclassing it...especially since delegates are mainly
used to avoid subclassing. For the specific case of limiting text
field input, why not just use an NSFormatter subclass, though? That's
what I'd do in Cocoa (and this is the cocoa-dev list, after all).
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