获得的json先转换成字符串
NSString *receiveStr = [[NSString alloc]initWithData:receiveData encoding:NSUTF8StringEncoding];
字符串再生成NSData
NSData * data = [receiveStr dataUsingEncoding:NSUTF8StringEncoding];
再解析
NSDictionary *jsonDict = [NSJSerialization JSONObjectWithData:data options:NSJSONReadingMutableLeaves error:nil];
http://www.cnblogs.com/wendingding/p/3950132.html