Retrieve object from NSArray by specifying class name

Question

The task:

Return an object from an NSArray that's instance of the class who's name is given as parameter to the function.

Right now I have this function:

+ (id)objectOfType:(NSString *)name fromArray:(NSArray *)array
{
   for (NSObject* instance in array)
   {
      if ([instance.className isEqualToString:name])
         return instance;
   }       
   return nil;
}

However, given that I can transform an array of objects into an array of class names of the objects with this simple method call on an NSArray

[array valueForKeyPath:@"className"]

shouldn't there also be a more concise way to retrieve the object with the specified class name..?

Depends on what you want to do. An array is a sorted list and the current implementation is returning the first match. There could of course be more. It could be done based on sets with a predicate filter but that would return a subset or subarray of all matches. Are you always looking for the first match or all? — pco494
– pco494, Commented Feb 14, 2016 at 8:41
In that case I think your implementation is fit for purpose. I think creating and parsing predicates is most likely far slower than the above approach, at least for reasonably sized arrays (a few hundred objects). — pco494
– pco494, Commented Feb 14, 2016 at 10:22

Avi · Accepted Answer · 2016-02-14 11:47:35Z

1

Here is a concise method, using NSPredicate and array filtering.

+ (id)objectOfType:(NSString *)name fromArray:(NSArray *)array {
    return [array filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"class == %@", NSClassFromString(name)]].lastObject;
}

answered Feb 14, 2016 at 11:47

Avi

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1 Comment

ATV Over a year ago

I guess that'll make for a nice category solving the task in a pretty concise way - cheers!

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