On 2 Feb 2010, at 06:39, BareFeet wrote:
>> On Jan 29, 2010, at 9:38 AM, Jerry Krinock wrote:
>>
>>>
>>> The problem is that when a subclass A is selected, the UI elements bound to
>>> subclass B no longer have valid bindings so generate an error. How can I
>>> solve this?
>>
>> You can also uncheck the "Raises For Not Applicable Keys" in the bindings
>> inspector pain in Interface Builder for your text fields.
>
> Thanks for the tip. Once I read it, it seemed like the logical solution.
> However, it doesn't seem to make any difference. All I could find in the
> documentation about that checkbox/attribute was:
>
> NSRaisesForNotApplicableKeysBindingOption
> An NSNumber object containing a Boolean value that specifies if an exception
> is raised when the binding is bound to a key that is not applicable—for
> example when an object is not key-value coding compliant for a key.
>
>
> To recall, I have something like this:
>
> @interface TopClass : NSObject
> {
> // some ivars
> }
>
> // some accessors
>
> @end
>
> @interface SubClass : TopClass
> {
> NSString* subValue;
> }
>
> - (NSString) subValue;
>
> @end
>
> I have an NSTreeController that contains a list of TopClass and SubClass
> items. The user selects an item in that list.
>
> I have a text field in Interface Builder whose value is bound (ie via
> bindings) to the subValue accessor, ie: NSTreeController -> selection.subValue
>
> Obviously, the subValue accessor is only valid if the currently selected item
> is a SubClass object. If the user selects a TopClass item, it throws an
> exception. How can I prevent this?
With "Raises for Not Applicable Keys" turned off, the exception will still be
thrown. But, the bound object will catch it and treat as a not applicable
result.
The only way not to throw the exception in the first place is to make
-valueForKey: return NSNotApplicableMarker. I'd suggest doing this by
overriding -valueForUndefinedKey:
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