Question

I have a NSSet containing many thousands of NSValue objects (wrapping CGPoints). I would like to very quickly find if a given CGPoint value exists in the NSSet. It seems to me that the member: method of an NSSet might do the job here, except that it checks for equality using isEqual:. NSValue objects use isEqualToValue:, and so when I execute the code:

[mySet member:valueToCheck];

it actually causes Xcode to crash.

1) Is there some way to use a custom equality check to make this work for NSValue objects?

2) Is this even the best approach (i.e. is member: quick enough in the first place)? The scenario is that I have a NSSet containing a large number of points representing pixels on the screen (iPad). Later on I need to bombard that set with many thousands of points per second to see if they exist in the set. My approach seems crude for achieving this. I thought about creating something like a huge 2-dimensional bit array, with each index representing a pixel on screen. Once I know the point I’m testing for, I can just jump straight to that point in the array and check for a 1 or 0… does this sound better or worse?

Thanks

Answer 1

Can you get this to a simple reproducible case? For example, I just tried:

NSValue *v = [NSValue valueWithCGPoint:CGPointMake(1, 1)];
NSSet *s = [NSSet setWithObject:v];
NSLog(@"%@", [s member:[NSValue valueWithCGPoint:CGPointMake(1, 1)]]);

But it works just fine.

edit

-isEqual: is not the problem:

NSValue *v1 = [NSValue valueWithPoint:NSMakePoint(1, 1)];
NSValue *v2 = [NSValue valueWithPoint:NSMakePoint(1, 1)];
NSLog(@"%d", [v1 isEqual:v2]); //logs "1"

-hash is not the problem:

NSLog(@"%d", ([v1 hash] == [v2 hash])); //logs "1"

They are different objects:

NSLog(@"%d", (v1 != v2)); //logs "1"

The problem is in your code. Try cleaning and rebuilding.