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）。

解析JSON 速度排名：http://hulefei29.iteye.com/blog/1757166

 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);
     }