Question

I have a Core Data model defined with two attributes

• (Double) latitude
• (Double) longitude

Now, I would like to fetched these objects and sort them depending on how far they are compared to the user’s current location. I already know how to get the current location, but what I still can’t figure out is how to sort the results depending on two attributes.

I’ve searched for something similar but I’m still a bit confused.

That’d be great if someone could point me to the right direction.

Thanks

Answer 1

Sorting with a comparator block is quite easy

NSArray *positions = //all fetched positions
CLLocation *currentLocation   = // You said that you know how to get this.


positions = [positions sortedArrayUsingComparator: ^(id a, id b) {
    CLLocation *locationA    = [CLLocation initWithLatitude:a.latitude longitude:a.longitude];
    CLLocation *locationB    = [CLLocation initWithLatitude:b.latitude longitude:b.longitude];
    CLLocationDistance dist_a= [locationA distanceFromLocation: currentLocation];
    CLLocationDistance dist_b= [locationB distanceFromLocation: currentLocation];
    if ( dist_a < dist_b ) {
        return (NSComparisonResult)NSOrderedAscending;
    } else if ( dist_a > dist_b) {
        return (NSComparisonResult)NSOrderedDescending;
    } else {
        return (NSComparisonResult)NSOrderedSame;
    }
}

As I just learned from lnafziger, you should add that useful hack/workaround¹, he is showing, to this.

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¹_{choose form this words the one, that has the most positive connotation for you}