void arraySort3() {      Student *stu1 = [Student studentWithFirstname:@"MingJie" lastname:@"Li"];      Student *stu2 = [Student studentWithFirstname:@"LongHu" lastname:@"Huang"];      Student *stu3 = [Student studentWithFirstname:@"LianJie" lastname:@"Li"];      Student *stu4 = [Student studentWithFirstname:@"Jian" lastname:@"Xiao"];      NSArray *array = [NSArray arrayWithObjects:stu1,stu2,stu3, stu4, nil nil];            // 利用block进行排序      NSArray *array2 = [array sortedArrayUsingComparator:       ^NSComparisonResult(Student *obj1, Student *obj2) {           // 先按照姓排序           NSComparisonResult result = [obj1.lastname compare:obj2.lastname];           // 如果有相同的姓，就比较名字           if (result == NSOrderedSame) {               result = [obj1.firstname compare:obj2.firstname];           }                      return result;      }];            NSLog(@"array2:%@", array2);  }