排序数组

排序数组最灵活的方法是使用 sortedArrayUsingComparator：方法。这接受 ^ NSComparisonResult（id obj1，id obj2）块。

 Return Value            Description
 NSOrderedAscending      obj1 comes before obj2
 NSOrderedSame           obj1 and obj2 have no order
 NSOrderedDescending     obj1 comes after obj2

例：

   NSArray *categoryArray = @[@"Apps", @"Music", @"Songs",
                     @"iTunes", @"Books", @"Videos"];
   
    NSArray *sortedArray = [categoryArray sortedArrayUsingComparator:
^NSComparisonResult(id obj1, id obj2) {
    if ([obj1 length] < [obj2 length]) {
        return NSOrderedAscending;
    } else if ([obj1 length] > [obj2 length]) {
        return NSOrderedDescending;
    } else {
        return NSOrderedSame;
    }
  }];

 NSLog(@"%@", sortedArray);