title: iOS: replace an object inside an array of array
body: <p>My code is:</p>
  
  <pre><code>[[arrayOne objectAtIndex:indexSelected] replaceObjectAtIndex:1 withObject:new];
  
  
  NSLog(@"indexSelected:%d", indexSelected); // = 0
  NSLog(@"new:%@", new); // = 26
  </code></pre>
  
  <p><code>indexSelected</code> is an int and <code>new</code> is a string</p>
  
  <p>When I try to do this I have an exception that says: <code>Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayI replaceObjectAtIndex:withObject:]: unrecognized selector sent to instance 0x1cee60'</code></p>
  
  <p>Why?</p>