iOS binary search code crash above 256 items - ios

Question

I've used iOS default code to search string in custom dictionary object which exist in array, Means array of dictionary items.
NSRange searchRange = NSMakeRange(0, artistThumbnail.count);
index = [artistThumbnail indexOfObject:artist
inSortedRange:searchRange
options:NSBinarySearchingLastEqual
usingComparator:^NSComparisonResult(id _Nonnull obj1, id _Nonnull obj2) {
NSString *artistName = (NSString *)obj2;
NSDictionary *artistThumbnail = (NSDictionary *)obj1;
NSString *artistToCompare = artistThumbnail[_artist_thumb];
NSComparisonResult result = [artistToCompare compare:artistName];
return result;
}];
When I used same code with less then equal to 256 objects code work fine no crash, both Obj1 and Obj2 have the dictionary object, but when array have >256 items then it crash and I've noticed that obj1 and obj2 not the same as the previously always come in NSDictionary format.

Answer 1

The problem is that your comparison object is of a different type than your array elements. If you type the array properly as NSArray<NSDictionary *> * you get a warning saying that parameter indexOfObject should be of type NSDictionary *.
Furthermore, you cannot rely on the artist object always is passed as obj2 to the comparison function. The documentation does not say anything about this, so you should assume that it can be passed as obj1 sometimes and obj2 other times.
To solve it you can embed the artist in a dictionary to make it the same format as an array element like this #{ _artist_thumb: artist }. Then you retrieve the name from both parameters the same way.
NSRange searchRange = NSMakeRange(0, artistThumbnail.count);
index = [artistThumbnail indexOfObject:#{ _artist_thumb: artist }
inSortedRange:searchRange
options:NSBinarySearchingLastEqual
usingComparator:^NSComparisonResult(id _Nonnull obj1, id _Nonnull obj2) {
NSString *artistName = ((NSDictionary *)obj2)[_artist_thumb];
NSDictionary *artistThumbnail = (NSDictionary *)obj1;
NSString *artistToCompare = artistThumbnail[_artist_thumb];
NSComparisonResult result = [artistToCompare compare:artistName];
return result;
}];