NSJSONSerialization介紹

　　ios5中apple增加了解析JSON的api——NSJSONSerialization。網上已經有人做過測試，NSJSONSerialization在效率上完勝SBJSON、TouchJSON、YAJL、JSONKit、NextiveJson。詳情見這里。既然apple為我們提供了這么良好的工具，我們沒理由不用吧。

　　NSJSONSerialization提供了將JSON數據轉換為Foundation對象（一般都是NSDictionary和NSArray）和Foundation對象轉換為JSON數據（可以通過調用isValidJSONObject來判斷Foundation對象是否可以轉換為JSON數據）。

　　下面提供一個從豆瓣電台下載的json數據轉換的代碼

　　

#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對象轉換為json數據

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);
    }