Question

NSString *url = @"http://localhost/xml";
NSURLRequest *req = [NSURLRequest requestWithURL:[NSURL URLWithString:url]];

[NSURLConnection sendAsynchronousRequest:req queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){
    NSDictionary *xmlDictionary = [XMLReader dictionaryForXMLData:data error:&error];
    int count = [[[xmlDictionary objectForKey:@"ArrayOfMessage"] objectForKey:@"Message"] count];
    if(true && count > 5) count = 5;

    UIScrollView *sv = [[UIScrollView alloc] initWithFrame:CGRectMake(58, 0, MESSAGE_PAGING_WIDTH, 493)];
    [sv setBounces:YES];
    [sv setClipsToBounds:NO];
    [sv setPagingEnabled:YES];
    [sv setShowsHorizontalScrollIndicator:FALSE];
    [sv setContentSize:CGSizeMake(count * MESSAGE_PAGING_WIDTH, frame.size.height)];

    int i = 0;
    while (i < count) {
        NSDictionary *data = [[[xmlDictionary objectForKey:@"ArrayOfMessage"] objectForKey:@"Message"] objectAtIndex:i];
        [sv addSubview:[[MessageView alloc] initWithFrame:CGRectMake(i * MESSAGE_PAGING_WIDTH, 0, 838, 493) data:data]];

        ++i;
    }

    [self addSubview:sv];
}];

I get a crash message of:

bool _WebTryThreadLock(bool), 0x7d7d080: Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread. Crashing now...

How can I remedy?

Answer 1

You’re creating UIKit elements on a different thread than the main thread:

This may be a result of calling to UIKit from a secondary thread.

sendAsynchronousRequest:queue:completionHandler: performs on a background thread. Inside your block you need to use performSelectorOnMainThread:withObject:waitUntilDone: for UIKit objects.

See http://blog.jayway.com/2010/03/30/performing-any-selector-on-the-main-thread/