归档
实现序列化机制 用某种格式把对象保存在指定文件 方便以后文件恢复
1 把对象写入指定文件 归档
2 把这种形式的文件从文件中恢复出来 解归档

//把字典dict写入File
NSMutableDictionary *dict = [NSMutableDictionary dictionary];
       [dict setObject:@"1" forKey:@"one"];
       [dict setObject:@"2" forKey:@"two"];
       [dict setObject:@"3" forKey:@"three"];
      BOOL ret =  [NSKeyedArchiver archiveRootObject:dict toFile:@"指定文件名"];
       if (ret)
       {
           NSLog(@"归档成功");
       }
       else
       {
           NSLog(@"归档失败");
       }

      //解归档
        id obj = [NSKeyedUnarchiver unarchiveObjectWithFile:@"指定文件名"];
        if ([obj isKindOfClass:[NSDictionary class]]) //判断数据类型
        {
            NSLog(@"dict = %@",obj);
        }