UI hanging on background rss parsing - ios

Question

I'm trying to create a simple rss reader. The code works okay, except the UI hangs when the feeds are being updated. I thought I cobbled together the code to get the feed and parse it on a background queue while updating the UI on the mainQueue, but the table hangs pretty badly. Code below:
-(void)refreshFeed2
{
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
for (NSString *feed in _feeds) {
// iterate over all feeds
NSLog(#"feed=%#", feed);
NSURL *url = [NSURL URLWithString:feed];
// Create url connection and fire request
NSURLConnection *conn = [[NSURLConnection alloc] init];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
(void)[conn initWithRequest:request delegate:self];
[NSURLConnection sendAsynchronousRequest:request queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
{
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
if ([data length] == 0 && error == nil) {
// handle empty response
} else if (error != nil) {
// handle error
NSLog(#"Error %#", [error localizedDescription]);
} else if ([httpResponse statusCode] == 200) {
// data present and no errors
[queue addOperationWithBlock:^{
// parse feed on queue
RXMLElement *rss = [RXMLElement elementFromXMLData:data];
RXMLElement *rssChild = [rss child:#"channel"];
RXMLElement* title = [rssChild child:#"title"];
NSArray* items = [[rss child:#"channel"] children:#"item"];
NSMutableArray* result=[NSMutableArray array];
for (RXMLElement *e in items) {
// iterate over the articles
RSSArticle* article = [[RSSArticle alloc] init];
article.sourceTitle = [title text];
article.articleTitle = [[e child:#"title"] text];
article.articleDescription = [[e child:#"description"] text];
article.articleUrl = [NSURL URLWithString: [[e child:#"link"] text]];
NSString *articleDateString = [[e child:#"pubDate"] text];
article.articleDate = [NSDate dateFromInternetDateTimeString:articleDateString formatHint:DateFormatHintRFC822];
if (article.articleUrl != NULL) {
[result addObject:article];
}
}
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
// update table on mainQueue
for (RSSArticle *article in result) {
// iterate over articles
int insertIdx = [_allEntries indexForInsertingObject:article sortedUsingBlock:^(id a, id b) {
RSSArticle *entry1 = (RSSArticle *) a;
RSSArticle *entry2 = (RSSArticle *) b;
return [entry1.articleDate compare:entry2.articleDate];
}];
[_allEntries insertObject:article atIndex:insertIdx];
[self.LeftTableView insertRowsAtIndexPaths:[NSArray arrayWithObject:[NSIndexPath indexPathForRow:insertIdx inSection:0]]
withRowAnimation:UITableViewRowAnimationFade];
}
}];
}];
}
}];
// Stop refresh control
[refreshControl endRefreshing];
}
}
Code that calls refreshFeed2:
- (void)viewDidLoad {
[super viewDidLoad];
self.allEntries = [NSMutableArray array];
self.feeds = [NSArray arrayWithObjects:
#"http://feeds.washingtonpost.com/rss/politics",
#"http://rss.cnn.com/rss/cnn_allpolitics.rss",
#"http://www.npr.org/rss/rss.php?id=1012",
#"http://www.slatedigital.com/support/feeds/rss_kb.php?s=fd5aa35e773dc3177b85a2126583f002",
nil];
}
//add refresh control to the table view
refreshControl = [[UIRefreshControl alloc] init];
[refreshControl addTarget:self
action:#selector(refreshInvoked:forState:)
forControlEvents:UIControlEventValueChanged];
NSString* fetchMessage = [NSString stringWithFormat:#"Fetching Articles"];
refreshControl.attributedTitle = [[NSAttributedString alloc] initWithString:fetchMessage
attributes:#{NSFontAttributeName:[UIFont fontWithName:#"Helvetica" size:11.0]}];
[self.LeftTableView addSubview: refreshControl];
[self refreshInvoked:self forState:UIControlStateNormal];
}
-(void) refreshInvoked:(id)sender forState:(UIControlState)state {
NSOperationQueue *refreshQueue = [[NSOperationQueue alloc] init];
[refreshQueue addOperationWithBlock:^{
[self refreshFeed2];
}];
}
Any help?
Thanks!

Answer 1

Can you try this? replace
[self refreshInvoked:self forState:UIControlStateNormal];
by
[self performSelectorOnBackground:#selector(refreshFeed2) withObject:nil];
and replace the same instead of
-(void) refreshInvoked:(id)sender forState:(UIControlState)state {
[self performSelectorOnBackground:#selector(refreshFeed2) withObject:nil ];
}