Asynchronous function execution?

Question

in my iOS app I do the following.

viewDidAppear(){

   // Load a spinner in a view on the top
   [DSBezelActivityView newActivityViewForView:self.view]; 
   // Execute code that require 3 seconds
   ...
   // Stop the spinner
   [DSBezelActivityView removeViewAnimated:YES];
}

The problem is that the spinner doesn't appear, because the the cpu is working hard (something similar). It's like that the code betweek the start and stop has precedence on the rendering of the view.

I would love to find a way to show effectively the start of the spinner, without using a timer to delay the code execution.

Thanks

Answer 1

If you have a method like

-(void) showSpinner:(UIView*)view {
    dispatch_async(dispatch_get_main_queue(), ^{
        [DSBezelActivityView newActivityViewForView:view];
    });
}

there are several ways to call it from a different thread. Choose one from the following:

[NSThread detachNewThreadSelector:@selector(showSpinner:) toTarget:self withObject:self.view];
// or 
[self performSelectorInBackground:@selector(showSpinner:) withObject:self.view];
// or 
NSInvocationOperation *invOperation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(showSpinner:) object:self.view];
NSOperationQueue *opQueue = [[NSOperationQueue alloc] init];
[opQueue addOperation:invOperation];
// or 
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    [self showSpinner:self.view];
});

Alt + click for details.