歸檔
實現序列化機制 用某種格式把對象保存在指定文件 方便以后文件恢復
1 把對象寫入指定文件 歸檔
2 把這種形式的文件從文件中恢復出來 解歸檔

//把字典dict寫入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(@"歸檔成功");
       }
       else
       {
           NSLog(@"歸檔失敗");
       }

      //解歸檔
        id obj = [NSKeyedUnarchiver unarchiveObjectWithFile:@"指定文件名"];
        if ([obj isKindOfClass:[NSDictionary class]]) //判斷數據類型
        {
            NSLog(@"dict = %@",obj);
        }