Re: Binding to selection of NSArrayController
Re: Binding to selection of NSArrayController
- Subject: Re: Binding to selection of NSArrayController
- From: Quincey Morris <email@hidden>
- Date: Tue, 23 Sep 2014 18:57:41 +0000
On Sep 23, 2014, at 11:36 , Lee Ann Rucker <email@hidden> wrote:
> On Sep 23, 2014, at 9:15 AM, Jonathan Taylor <email@hidden> wrote:
>>
>> [*] One slight glitch - if I add an object to the NSMutableArray then it does not immediately show up in the table, I have to call will/didChangeValueForKey on the property that returns the array. I don’t know if that is expected behaviour (maybe I should be adding via the array controller somehow?). This is not a problem, but I mention it for completeness, just in case it’s indicative of something funny that is going on that I don’t fully appreciate.
>
> Yes, it’s complicated. The ArrayController doesn’t know about changes that are made directly to the NSMutableArray. You can use [NSArrayController addObject:] for simple cases, or spend a lot of time with the KVC programming guide, especially “Collection accessor patterns for to-many properties”.
In fact, Lee Ann is being a little bit kind here, because Jonny really is Doing It Wrong™.
Because the UI is using bindings, it is *necessary* to update the array KVO-compliantly. Simply adding objects to the NSMutableArray isn’t KVO-compliant, hence the lack of automatic updating of the UI.
The underlying problem is in thinking of the data (that is, the “M” in MVC) as an array instead of a indexed to-many property. When you make that conceptual change, then, yes, you end up in a deep relationship with the KVC programming guide.
There is** a quick and dirty way of fixing this, though, without cracking open any programming guides. Anywhere that you update the NSMutableArray (either by referencing its instance variable “myArray” or “_myArray”, or a property “someObject.myArray" that provides access to that instance variable), you can use a mutable proxy instead. For example, in the class that has the array, instead of:
[_myArray addObject: something];
or:
[self.myArray addObject: something];
you would write:
[[self mutableArrayValueForKey: @“myArray”] addObject: something];
and you should magically see the updates start working. But the KVC programming guide is a better bet for a long-term relationship.
** Subject to the proviso that I’m just writing this, not doing it ATM, so I may have missed something.
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