Re: Selecting an object based on the value of one of its attributes
Re: Selecting an object based on the value of one of its attributes
- Subject: Re: Selecting an object based on the value of one of its attributes
- From: Lynn Barton <email@hidden>
- Date: Mon, 03 May 2010 15:24:43 -0700
Roland, the application in question uses Core Data. To build a dictionary as you suggest, I will need to wait until the array controller loads its content, then iterate over all members of the array, putting the property in question and the array index into the dictionary. How can I know immediately (without any user action) that the content has finished loading? I can't use awakeFromNib, as the content has not yet been loaded when that method is called.
--Lynn
On Apr 27, 2010, at 8:06 PM, Roland King wrote:
> Graham Cox wrote:
>> On 28/04/2010, at 12:37 PM, Lynn Barton wrote:
>>> Newbie question: Consider an array of dictionary objects, all of the same class. One of the ivars of that class is an NSString which is unique for each instance. Does there already exist a method that will identify the one dictionary object that has a given value of that ivar, without me having to write code to examine all of the objects one by one? I have searched the documentation without finding such a method.
>>> Lynn Barton
>> You could use NSPredicate to "filter" your collection based on your unique string property being equal to the one sought. If they are unique it will return exactly one item (or none, if it doesn't exist).
>> See [NSArray filteredArrayUsingPredicate:]
>> It's unclear whether that would be actually any faster than doing a linear search yourself - it might be slower, in that it wouldn't return as soon as it found the item, but would always check every element.
>> --Graham
>
> I think that as Graham suggests that would be slower than searching yourself, but it is a method and it does exist and it's "free", so you could try that and if it's fast enough for you, that's great.
>
> Actually iterating the list however yourself is very simple and possibly only the same number of lines of code as making a predicate. (code typed in mail)
>
> YourObject *found = nil;
> for( YourObject *obj in yourArrayOfObjects )
> if( [ [ obj thePropertyYouWant ] isEqualToString:yourThing ] )
> {
> found = obj;
> break;
> }
> // if found isn't nil, you found one, if it is, you failed.
>
> Finally - are these all your objects and are you always looking for the same property of them? If so instead of dumping them into an array you could build a dictionary of them as you insert them, keyed by that string property, then go look it up later when you want it.
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