On Aug 9, 2012, at 7:58 AM, Koen van der Drift wrote:
> Maybe I should use a predicate, something like this:
>
> valueFilter = [NSPredicate predicateWithFormat:@"%@ < value < %@",
> self.minimumValue, self.maximumValue];
> [myArrayController setFilterPredicate: valueFilter];
>
> As I said I'm not able to test it until later today, but I wanted to
> throw it out to see if there are any comments/suggestions. The two
> values are bound to the textfields, so hopefully this will update the
> display automagically when the user changes the value(s).
You should definitely use a predicate but it will not automagically update.
The predicate you create above is fixed. The _values at the time of the call_
to -predicateWithFormat: are incorporated into the predicate. The predicate
does _not_ incorporate references to the "self" object nor the key paths
"minimumValue" or "maximumValue". It can't and that's inherent in the C
function call semantics (a.k.a. the Objective-C method call semantics).
Arguments are passed by value, not reference. (At a higher conceptual level,
you can pass a reference by passing a pointer, but the pointer itself is passed
by value.)
You might be able to achieve what you want by making a property on the objects
in the array which refers back to the controller and using a predicate like
"value between { controller.minimumValue, controller.maximumValue }". However,
putting such a reference to the controller is poor design and may be
inappropriate for a number of reasons: the same array may be displayed in
multiple tables with different controllers, the same objects may be in multiple
arrays, etc.
Better would be to create a property on your controller which returns the
predicate, constructing it on demand for each call (perhaps with some smart
caching). (I'll call the property "minMaxPredicate" for discussion.) Bind the
array controller's filterPredicate binding to that property on your controller.
Then, arrange for KVO change notifications to be emitted for the property when
the minimum and maximum value properties change. The easiest way to do this is
to add a method like the following to your class:
+ (NSSet *) keyPathsForValuesAffectingMinMaxPredicate
{
return [NSSet setWithObjects:@"minimumValue", @"maximumValue", nil];
}
See the documentation for the method +keyPathsForValuesAffectingValueForKey:
and the section Registering Dependent Keys in the Key-Value Observing
Programming Guide to understand why this works.
<https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/KeyValueObserving/Articles/KVODependentKeys.html>
Regards,
Ken
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