Question

I am using blocks in iPhone and inside that I am just showing an UIAlertView with a title and text.
The problem is that the alert view sometimes has very long to appear.
On other areas its working fine.
Can anyone suggest me what may be the reason?

Answer 1

UI* elements must be handled from the main thread. If you use a block to run something in the background wrap all calls to UI* in the dispatch_queue of the main thread.

like this:

dispatch_async(myQueue, ^{
    // do something in background
    dispatch_async(dispatch_get_main_queue(), ^{
        // Interaction with User Interface Elements on the main thread...
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Foo" message:@"Bar" delegate:nil cancelButtonTitle:@"Cancel" otherButtonTitles:@"OK", nil];
        [alert show];
    });
});