nsmutablearray - iOS - What exactly does allKeys: return in an NSArray, and how to alphabetize? -

I'm trying to create an array of keys from a NSMutableDictionary , and then click it Sort alphabetically What I just got:

  _currentItemsArray = (NSMutableArray *) [_ currentItemsDict allKeys]; [_currentItemsArray sortUsingSelector: @selector (Case Incentive Compaire :));   
 But this is throwing an exception. Specifically:  
  - [__NASRRI sorting selector:]: 0x1e54ddb0 sent to the unknown selector for example   
 My research is telling me that This means that  _currentItemsArray  is not  NSString  's   NSString ' s  
 and in any way , Is this the best way to sort a  all of  array alphabetically?  
  
 
 
 You can have your  currentItemsArray  to an NSArray Pointer NSMutableArray Indicator An NSMutableArray, but any amount (NSMutableArray *) entered can make NSArray unstable, you must use NSArray methods:   NSArray * array = [[_currentItemsDict allKeys] SortedAreasy user: @Selector (if any)];