queued view updates not happening when performSelector afterDelay:0 used

I have an app that performs some calculations based on data arriving on a socket or local user interaction.

I want to show an 'activity spinner' whilst the calculation happens.

spinner = [[UIActivityIndiactorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
[spinner setCenter:self.view.center];
[self.view addSubview:spinner];
[spinner startAnimating];
[self performSelector:@selector(doCalcs) withObject:nil afterDelay:0];

This works well, except in the case where the code is run as a result of a message arriving over the network. I'm using http://code.google.com/p/cocoaasyncsocket/ to handle sockets and the code is running in the onSocket:didReadData:withTag: method.

'doCalcs' takes a few seconds. The spinner doesn't appear whilst it's running.

If I change afterDelay:0 to afterDelay:1 then the spinner does appear the whole time doCalcs is running, but with the downside that i开发者_C百科t takes an extra second. So it seems the code is all correct, but for whatever reason the spinner isn't getting a chance to get on screen before doCalcs runs.

Any suggestions would be most welcome.

You could try doing your calculations on a background thread to prevent the animation from blocking:

[self performSelectorInBackground:@selector(doCalcs)withObject:nil];

Instead of a selector, you need to spawn a thread to do your calculations. UI Only updates if the app allows trips through the event loop. and your method is blocking. Alternatively, you can have a timer call your "doCalcs" method periodically until they are complete... it should exit after a set period of time so the event loop can execute and do the calcs in "slices". If you need further direction let me know!