Foundation对象转化Json对象

示例：

NSDictionary *dic=[NSDictionary  dictionaryWithObjectsAndKeys:@"uid",@"_id",@"name",@"loginName",@"pass",@"password" , nil];    //判断Foundation对象能否转化为json对象    if ([NSJSONSerialization isValidJSONObject:dic]) {        NSError *error;        //NSJSONWritingPrettyPrinted将生成的json数据格式化输出，        NSData *data=[NSJSONSerialization dataWithJSONObject:dic options:NSJSONWritingPrettyPrinted error:&error];
        NSLog(@"Register JSON:%@",[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]);