NSArray *array = [NSArray arrayWithObjects:@"", @"", @"", @"", nil];

NSArray *array2 = [array sortedArrayUsingSelector:@selector(compare:)];

//sortedArrayUsingSelector:@selector() 方法会把数组array中的元素按指定元素的比较方法compare: 返回一个排好序的数组（默认从小到大），原数组的元素顺序不会改变；

//注：sortedArrayUsingSelector:@selector()的参数是传一个方法参数。

//先在其他类中实现如下方法：Start

+ (id)studentWithFirstname:(NSString *)firstname lastname:(NSString *)lastname { //此方法创建对象时调用

    Student *stu = [[[Student alloc] init] autorelease];

    stu.lastname = lastname;

    stu.firstname = firstname;

    return stu;

}

-(NSComparisonResult)compareStudent:(Student *)stu

{        // 先按照姓排序

    NSComparisonResult result = [self.lastname compare:stu.lastname];

    if (result == NSOrderedSame) {    //默认按照ASCII码表中的顺序排序，如果有相同的姓，就比较名字。

        result = [self.firstname compare:stu.firstname];

    }

    return result;

}

+ (id)studentWithFirstname:(NSString *)firstname lastname:(NSString *)lastname bookName:(NSString *)bookName {

    Student *stu = [Student studentWithFirstname:firstname lastname:lastname];

    stu.book = [Book bookWithName:bookName];

    return stu;

}

+ (id)bookWithName:(NSString *)name {

    Book *book = [[[Book alloc] init] autorelease];

    book.name = name;

    return book;

}

-(NSString *)description

{

    //重写description方法是输出结果从内存地址变为可读的对象名如：Li MingeJie

   return [NSString stringWithFormat:@"[%@ %@-%@]", self.lastname, self.firstname, self.book.name];

}

//先在其他类中实现如上方法：End

Student *stu1 = [Student studentWithFirstname:@"MingJie" lastname:@"Li"];

Student *stu2 = [Student studentWithFirstname:@"XiaoXu" lastname:@"Zhang"];

Student *stu3 = [Student studentWithFirstname:@"LianJie" lastname:@"Li"];

Student *stu4 = [Student studentWithFirstname:@"LiDa" lastname:@"Zhang"];

NSArray *array = [NSArray arrayWithObjects:stu1,stu2,stu3, stu4, nil];

//创建的四个对象存进数组array中。

NSArray *array2 = [array sortedArrayUsingSelector:@selector(compareStudent:)]; //指定排序的比较方法compareStudent: ，这个方法为在类中实现的方法。

Student *stu1 = [Student studentWithFirstname:@"MingJie" lastname:@"Li"];

Student *stu2 = [Student studentWithFirstname:@"XiaoXu" lastname:@"Zhang"];

Student *stu3 = [Student studentWithFirstname:@"LianJie" lastname:@"Li"];

Student *stu4 = [Student studentWithFirstname:@"LiDa" lastname:@"Zhang"];

NSArray *array = [NSArray arrayWithObjects:stu1,stu2,stu3, stu4, nil];

//创建的四个对象存进数组array中。

NSArray *array2 = [array sortedArrayUsingComparator:^NSComparisonResult(Student *obj1, Student *obj2)

{//sortedArrayUsingComparator: 方法 是利用block进行排序，每当进行两个元素的比较时都会调用这个Block进行比较；Block为sortedArrayUsingComparator: 方法的参数。

    NSComparisonResult result = [obj1.lastname compare:obj2.lastname];　　// 先按照姓排序

    if (result == NSOrderedSame) {//默认按照ASCII码表中的顺序排序，如果有相同的姓，就比较名字

        result = [obj1.firstname compare:obj2.firstname];

    }

    return result;

}];

Student *stu1 = [Student studentWithFirstname:@"MingJie" lastname:@"Li" bookName:@"book1"];

Student *stu2 = [Student studentWithFirstname:@"XiaoXu" lastname:@"Zhang" bookName:@"book2"];

Student *stu3 = [Student studentWithFirstname:@"LianJie" lastname:@"Li" bookName:@"book2"];

Student *stu4 = [Student studentWithFirstname:@"LiDa" lastname:@"Zhang" bookName:@"book1"];

NSArray *array = [NSArray arrayWithObjects:stu1,stu2,stu3, stu4, nil];

NSSortDescriptor *bookNameDesc = [NSSortDescriptor sortDescriptorWithKey:@"book.name" ascending:YES];

//NSSortDescriptor 为排序描述类型，bookNameDesc 为排序描述类型对象；sortDescriptorWithKey: 方法先按照指定的书名@"book.name"进行排序, 这里的key(book.name中的book)写的是@property的名称；ascending:代表升序。

//再按照姓进行排序：

NSSortDescriptor *lastnameDesc = [NSSortDescriptor sortDescriptorWithKey:@"lastname" ascending:YES];

//再按照名进行排序：

NSSortDescriptor *firstnameDesc = [NSSortDescriptor sortDescriptorWithKey:@"firstname" ascending:YES];

//按顺序添加排序描述器descs：bookNameDesc、lastnameDesc、firstnameDesc可根据实际需求按顺序写在代码中，决定着排序的优先级，先写的先按此标准排序：

NSArray *descs = [NSArray arrayWithObjects:bookNameDesc, lastnameDesc, firstnameDesc, nil];//此处的descs是一个设置好顺序的顺序描述器，而非寻常数组。

NSArray *array2 = [array sortedArrayUsingDescriptors:descs];

//sortedArrayUsingDescriptors: 方法把排序描述器descs按其内部已经指定好的顺序排好顺序并返回一个排好顺序的数组。

NSLog(@"array2:%@", array2);//此处的数组array2是一个按需求排好顺序的新数组。