NSJSONSerialization介绍

　　ios5中apple增加了解析JSON的api——NSJSONSerialization。网上已经有人做过测试，NSJSONSerialization在效率上完胜SBJSON、TouchJSON、YAJL、JSONKit、NextiveJson。详情见这里。既然apple为我们提供了这么良好的工具，我们没理由不用吧。

　　NSJSONSerialization提供了将JSON数据转换为Foundation对象（一般都是NSDictionary和NSArray）和Foundation对象转换为JSON数据（可以通过调用isValidJSONObject来判断Foundation对象是否可以转换为JSON数据）。

　　下面提供一个从豆瓣电台下载的json数据转换的代码

View Code

#define kGlobalQueue    dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0)
#define kDoubanUrl      @"http://douban.fm/j/mine/playlist?type=n&h=&channel=0&from=mainsite&r=4941e23d79"
-(void) loadJsonData:(NSURL *)url
{dispatch_async(kGlobalQueue, ^{NSData *data = [NSData dataWithContentsOfURL:url];[self performSelectorOnMainThread:@selector(parseJsonData:) withObject:data waitUntilDone:NO];});
}
-(void) parseJsonData:(NSData *)data
{NSError *error;NSDictionary *json = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];if (json == nil) {NSLog(@"json parse failed \r\n");return;}NSArray *songArray = [json objectForKey:@"song"];NSLog(@"song collection: %@\r\n",songArray);_song = songArray;self.songIndex = 0;NSDictionary *song = [songArray objectAtIndex:0];NSLog(@"song info: %@\t\n",song);
}

　　Foundation对象转换为json数据

View Code

NSDictionary *song = [NSDictionary dictionaryWithObjectsAndKeys:@"i can fly",@"title",@"4012",@"length",@"Tom",@"Singer", nil];if ([NSJSONSerialization isValidJSONObject:song]){NSError *error;NSData *jsonData = [NSJSONSerialization dataWithJSONObject:song options:NSJSONWritingPrettyPrinted error:&error];NSString *json =[[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];NSLog(@"json data:%@",json);}