sortedArrayUsingComparator

1.降序

 NSArray *tMlist = @[@4,@5,@2,@6,@3,@7,@8]; //降序序8，7，。。 NSArray *tArray = [tMlist sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2)                    {                        NSNumber *tNumber1 = (NSNumber *)obj1;                        NSNumber *tNumber2 = (NSNumber *)obj2;                        //因为不满足sortedArrayUsingComparator方法的默认排序顺序，则需要交换                         if ([tNumber1 integerValue] < [tNumber2 integerValue])                             return NSOrderedDescending;                         return NSOrderedAscending;                         //因为满足sortedArrayUsingComparator方法的默认排序顺序，则不需要交换                        if ([tNumber1 integerValue] > [tNumber2 integerValue])                             return NSOrderedAscending;                         return NSOrderedDescending;

2 升序

 NSArray *tMlist = @[@4,@5,@2,@6,@3,@7,@8]; //结果：升序2，4，。。 NSArray *tArray = [tMlist sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2)                    {                        NSNumber *tNumber1 = (NSNumber *)obj1;                        NSNumber *tNumber2 = (NSNumber *)obj2;                         //因为满足sortedArrayUsingComparator方法的默认排序顺序，则不需要交换                        if ([tNumber1 integerValue] < [tNumber2 integerValue])                            return NSOrderedAscending;                        return NSOrderedDescending;                        // 因为不满足sortedArrayUsingComparator方法的默认排序顺序，则需要交换。                        // if ([tNumber1 integerValue] < [tNumber2 integerValue])                        //       return   NSOrderedAscending ;                        //   return NSOrderedDescending;                    }];

3 数组逆转

NSArray *tMlist = @[@4,@5,@2,@6,@3,@7,@8]; NSArray *tArray = [tMlist sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2)                    {                        NSNumber *tNumber1 = (NSNumber *)obj1;                        NSNumber *tNumber2 = (NSNumber *)obj2;                        //数组逆转                        return NSOrderedDescending;                    }];

4.数组不变

NSArray *tMlist = @[@4,@5,@2,@6,@3,@7,@8]; NSArray *tArray = [tMlist sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2)                    {                        NSNumber *tNumber1 = (NSNumber *)obj1;                        NSNumber *tNumber2 = (NSNumber *)obj2;                        //数组不变                         return NSOrderedAscending;                    }];

总结：

1.sortedArrayUsingComparator这个方法本身就是按递增的方式排序。2.返回的返回值（NSOrderedAscending 不交换，NSOrderedSame 不交换，NSOrderedDescending 交换）。例如：object1 < object2 返回：NSOrderedDescending 则交换（变为object2，object1），以保证安方法本身升序。返回NSOrderedAscending，两者不交换。

对于Comparator的返回值文档有下面的说明

• NSOrderedAscending
  
  • The left operand is smaller than the right operand.
• NSOrderedSame
  
  • The two operands are equal.
• NSOrderedDescending
  
  • The left operand is greater than the right operand

如果你期望的是值小的在前而值大的在后（升序），则可以在比较的时候返回NSOrderedAscending（-1），否则，就是NSOrderedDescending（1）。