Re: Binding to selection of NSArrayController
Re: Binding to selection of NSArrayController
- Subject: Re: Binding to selection of NSArrayController
- From: Jonathan Taylor <email@hidden>
- Date: Tue, 23 Sep 2014 22:40:53 +0100
Thankyou both for your advice - it's good to have you set me right on that one. Fortunately mine is a relatively uncomplicated case, and so [NSArrayController add/removeObject:] should do the job nicely
It feels a bit odd doing it that way, just because it makes the NSArray almost redundant in the whole thing - it's declared as a backing store, but this way I don't actually end up accessing it for anything. There's a rather long and redundant-seeming chain running from NSArray instance variable -> property -> binding -> NSArrayController -> IBOutlet -> instance variable that I actually manipulate. Oh well, if that's the way it's meant to be...
On 23 Sep 2014, at 19:57, Quincey Morris <email@hidden> wrote:
> 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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