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POShow UIActivityIndicator during segue navigation, after UIBarButtonItem press
 

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    <p>I have a UIBarButtonItem in the navigation bar which switches to another screen, using a segue. This other screen takes some time to initialize, and I wanted to put a UIActivityIndicator on the UIBarButtonItem to show the tap has been registered, and the iPad is busy executing the action. </p> <p>My approach was to add a UIActivityIndicator to the UIBarButtonItem after it was pressed, then call <code>performSegueWithIdentifier:</code>, and in the <code>viewDidLoad</code> method of the second view, put the initialization into a <code>dispatch_sync()</code> call. You can guess it does not work... why?</p> <p>The IBAction on the first screen:</p> <pre><code>- (void)tappedEdit: (UIBarButtonItem *)editButton { // put activity indicator somewhere UIActivityIndicatorView *indicator; indicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge]; indicator.frame = CGRectMake (200, 5, 50, 50); [self addSubview: indicator]; [indicator startAnimating]; // follow segue [self performSegueWithIdentifier: SegueShowDesignMode sender: editButton]; } </code></pre> <p>The initialization on the second screen:</p> <pre><code>- (void)viewDidLoad { [super viewDidLoad]; // put costly operations into another queue to free main queue for activity indicator dispatch_sync (dispatch_get_global_queue (0, 0), ^{ // do initialization here }); } </code></pre> <p>The effect of this is that the UIBarButtonItem stays tapped while the initialization is performed, then the UIActivityIndicator is visible for a quick moment, and lastly the segue animation is shown, displaying the second screen. </p> <p>Any idea? Thanks a lot!</p> <p>EDIT: Probably an addition to the problem is that the initialization does some UIKit stuff: When I tried to use a semaphore, the initialization dumps with a BAD ACCESS in some UITextView method. I guess this is because it runs on some 'get_global_queue' and not on the 'get_main_queue'.</p> <p>EDIT AGAIN: Well, no. Using 'get_main_queue' results in a dead-lock, as announced in the Apple docs. So the question boils down to </p> <p>"How can I do background UIView creation (lots of!) while still having a spinner running?"</p>
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