1. ButtonIndex of cancel is 0
// Add Cancel in init
UIActionSheet *actionSheet = [[UIActionSheet alloc]initWithTitle:nil delegate:self cancelButtonTitle:@"Cancel" destructiveButtonTitle:nil otherButtonTitles:nil];
[actionSheet addButtonWithTitle:@"MyItem"];

// Add Cancel after init (I prefer this way)
UIActionSheet *actionSheet = [[UIActionSheet alloc]initWithTitle:nil delegate:self cancelButtonTitle:nil destructiveButtonTitle:nil otherButtonTitles:nil, nil];
actionSheet.cancelButtonIndex = [actionSheet addButtonWithTitle:@"Cancel"];
[actionSheet addButtonWithTitle:@"MyItem"];
  1. ButtonIndex of cancel is last one

Add Cancel and other buttons in init, buttonIndex of cancel button is the last one, done is 0, option1 is 1.

 
UIActionSheet *actionSheet = [[UIActionSheet alloc]initWithTitle:nil delegate:self cancelButtonTitle:@"Cancel" destructiveButtonTitle:nil otherButtonTitles:@"Done", @"Done2", nil];
[actionSheet addButtonWithTitle:@"MyItem"];