On Sep 14, 2009, at 17:17, Todd Heberlein wrote:
(1) Why does [myNum isMemberOfClass:[NSNumber class]] return NO
when I explicitly did an [NSNumber alloc]?
(2) [myNum isKindOfClass:[NSNumber class]] returns YES, so what
type of subclasses are there to NSNumber?
(3) After changing the value in the text field, myNum is neither an
NSNumber of even a kind of NSNumber. What is it?
(4) I guess the answer to 3 might explain this, but after the
number is changed, why does myNum still respond to intValue but
*not* unsignedLongValue?
1. Because NSNumber is a class cluster with no concrete instances.
[NSNumber alloc] always returns a subclass.
2. It's an implementation detail we don't care about. If you look at a
NSNumber in the debugger, it should show you the actual class, if you
must know.
3. It's a NSString.
4. The answer to 3 does explain this. :) Strings do respond to
intValue etc, but not to unsignedXxxValue methods.
I am trying to understand the behavior of an NSNumber bound to an
NSTextField.
The underlying problem is that you can't get this understanding,
because a user interface item isn't bound to an *object* but to a
*property* of an object. In this case, your NSNumber object is
actually "neither of the above" -- it's the *value* of the property of
an object.
When you edit a text field, the property value is replaced by the text
field value -- which happens to be a string. (And yes, that's going to
mess things up with your NSNumber* @property definition.)
The simple solution is to add a number formatter to your text field.
Then, changing the text field causes it to update the binding with a
NSNumber value instead of a NSString value.
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