NSXMLParsing返回（null）

Question

我正在尝试解析在线xml文档，但每次运行脚本时它似乎都会返回（null）。我的解析方法有什么问题？

@implementation ViewController
NSString *livescore;
- (void)viewDidLoad
{
    [super viewDidLoad];

    NSURL *url = [NSURL URLWithString:@"http://www.scorespro.com/rss2/live-soccer.xml"];
    NSData* data = [NSData dataWithContentsOfURL:url];



    NSXMLParser* parser = [[NSXMLParser alloc] initWithData: data];

    [parser setDelegate:self];
    [parser parse];

}


- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qualifiedName attributes:(NSDictionary *)attributeDict {
    if ([elementName isEqualToString:@"channel"]) {

        livescore = attributeDict[@"title"];

        NSLog(@"%@", livescore);




    }


}