Question

I have an app which uses a UISearchBar to dynamically search from an external API based on user input.

The app is searching the external API fine and displaying results correctly, but when I select any row from the search results, the screen freezes and I am getting this error;

Tried to obtain the web lock from a thread other than the main thread or the web thread
UIKit should not be called from a secondary thread

I have absolutely no idea how I can fix this.

Here is the code;

- (void) run: (id) param  {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    NSXMLParser *parser = [[NSXMLParser alloc] initWithContentsOfURL: [self URL]];
    [parser setDelegate: self];
    [parser parse];
    [parser release];
    [delegate parseDidComplete];
    [pool release];
} 

- (void) parseXMLFile: (NSURL *) url
{ 
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    [self setURL: url];
    NSThread* myThread = [[NSThread alloc] initWithTarget:self
                                                 selector:@selector(run
   object: nil];
    [myThread start];
    [pool release];
}

Answer 1

“Tried to obtain the web lock from a
thread other than the main thread or
the web thread UIKit should not be
called from a secondary thread”

The fix is conceptually simple; don’t update the UI from your thread.

Assuming the parseDidComplete is where the message is sourced, then something like this will “work”:

[delegate performSelectorOnMainThread: @selector(parseDidComplete) withObject: nil waitUntilDone: YES];

“Work” because threading is hard and this answer completely ignores any synchronization issues you might have.

Note that you’d be better off using NSOperation and NSOperationQueue. They are well documented and there are a bunch of examples.