Thread Signal SIGABRT Exception - ios

Question

I'm curious to know why I'm receiving an exception on this code and as to what this exception means. When I remove the for loop, as indicated below, it works fine. When I include it, I get an exception.
-(void) loadVenues {
NSString *latLon = #"34.0500, -118.2500"; // approximate latLon of The Mothership (a.k.a Apple headquarters)
NSString *clientID = kCLIENTID;
NSString *clientSecret = kCLIENTSECRET;
//34.0500° N, 118.2500
NSDictionary *queryParams = #{#"ll" : latLon,
#"client_id" : clientID,
#"client_secret" : clientSecret,
#"categoryId" : #"4bf58dd8d48988d1e0931735",
#"v" : #"20140118"};
[[RKObjectManager sharedManager] getObjectsAtPath:#"/v2/venues/search"
parameters:queryParams
success:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {
_venues = mappingResult.array;
NSMutableArray *temp = [(NSArray*)_venues mutableCopy];
for (int i =0; i < _venues.count; i++)
{
NSUInteger index = 0;
for (int j = 0; j <_venues.count; j++)
{
//((MyObjectType *) [myArray objectAtIndex:0]).intProperty = 12345;
if(((Venue *) [temp objectAtIndex:index]).location.distance > 0)
{
Venue *holder= [temp objectAtIndex:index];
[temp removeObjectAtIndex:index];
NSUInteger indexer = index +1;
[temp addObject:[temp objectAtIndex:indexer]];
//replace a with a+1
[temp replaceObjectAtIndex:indexer withObject:holder];
//[temp addObject:holder atIndex: index+1];
//a[i+1]=holder;
index++;
}
else {index++;}
}
}
_venues = temp;
[self.tableView reloadData];
}
failure:^(RKObjectRequestOperation *operation, NSError *error) {
NSLog(#"What do you mean by 'there is no coffee?': %#", error);
}
];
}
I'm getting an exception at this line:
[temp addObject:[temp objectAtIndex:indexer]];
And I'm not sure why.
Here is the error:
2014-07-02 21:43:12.536 CoffeeKit[63581:60b] I restkit:RKLog.m:33 RestKit logging initialized...
2014-07-02 21:43:12.655 CoffeeKit[63581:60b] I restkit.network:RKObjectRequestOperation.m:150 GET 'https://api.foursquare.com/v2/venues/search?categoryId=4bf58dd8d48988d1e0931735&client_id=ZE5VJOPEO1PP3NDFVCM3O2ZUXWDDJRB20XDDGH3OETBKOVZB&client_secret=5LGY2CEASBQZQS5P0LYFICWDKMDOHJJ00F3G24LT4J4DX4X3&ll=34.0500%2C%20-118.2500&v=20140118'
2014-07-02 21:43:13.085 CoffeeKit[63581:f03] I restkit.network:RKObjectRequestOperation.m:220 GET 'https://api.foursquare.com/v2/venues/search?categoryId=4bf58dd8d48988d1e0931735&client_id=CLIENT_ID&client_secret=CLIENT_SECRET&ll=34.0500%2C%20-118.2500&v=20140118' (200 OK / 30 objects) [request=0.4171s mapping=0.0128s total=0.4486s]
2014-07-02 21:43:13.087 CoffeeKit[63581:60b] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 29 beyond bounds [0 .. 28]'
*** First throw call stack:
(
0 CoreFoundation 0x00000001023a0495 __exceptionPreprocess + 165
1 libobjc.A.dylib 0x00000001020ff99e objc_exception_throw + 43
2 CoreFoundation 0x0000000102346745 -[__NSArrayM objectAtIndex:] + 213
3 CoffeeKit 0x0000000100002efa __34-[MasterViewController loadVenues]_block_invoke + 602
4 CoffeeKit 0x000000010009310b __66-[RKObjectRequestOperation setCompletionBlockWithSuccess:failure:]_block_invoke244 + 91
5 libdispatch.dylib 0x0000000102c9a851 _dispatch_call_block_and_release + 12
6 libdispatch.dylib 0x0000000102cad72d _dispatch_client_callout + 8
7 libdispatch.dylib 0x0000000102c9d3fc _dispatch_main_queue_callback_4CF + 354
8 CoreFoundation 0x00000001023fe289 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
9 CoreFoundation 0x000000010234b854 __CFRunLoopRun + 1764
10 CoreFoundation 0x000000010234ad83 CFRunLoopRunSpecific + 467
11 GraphicsServices 0x00000001033e2f04 GSEventRunModal + 161
12 UIKit 0x0000000100cace33 UIApplicationMain + 1010
13 CoffeeKit 0x0000000100003733 main + 115
14 libdyld.dylib 0x0000000102efe5fd start + 1
15 ??? 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)

Answer 1

As you can see from your stack, your error is occurring because you attempt to access the object at index 29, which is outside of the array's bounds:
* -[__NSArrayM objectAtIndex:]: index 29 beyond bounds [0 .. 28]
In your case, it's probably arising from this line:
NSUInteger indexer = index +1;
[temp addObject:[temp objectAtIndex:indexer]];
Which I'm assuming you're using to get the value of the next object. Once the array reaches the 28th object, however, you attempt to access the imaginary 29th object.
Bottom line: refactor your code so that you only access objects that exist.

Answer 2

You are getting out of bounds by accessing the NEXT element in the array, 2 things. you can directly use 'j' to access the element (instead of index, so u dont have to increment it urself) and you can change your for from
for (int j = 0; j <_venues.count; j++)
to
for (int j = 0; j <_venues.count-1; j++)
By the way if all you need is sorting, NSMutableArray offers many options:
Rearranging Content
– exchangeObjectAtIndex:withObjectAtIndex:
– sortUsingDescriptors:
– sortUsingComparator:
– sortWithOptions:usingComparator:
– sortUsingFunction:context:
– sortUsingSelector: