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Editorial Team
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Asked: 2026-05-12T21:50:11+00:00

I’m trying to add a progress meter, or other I’m busy right now notification

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I’m trying to add a progress meter, or other “I’m busy right now” notification to my view hierarchy right before doing some intense computation that will block the UI. My code looks some thing like:

//create view
[currentTopView addSubView:imBusyView];

//some initialization for the intense computation
[computation startComputing];

Unfortunately, my progress meter doesn’t display until after the computation completes. It appears like the views aren’t re-drawn until the run loop completes. I’m pretty sure that setNeedsDisplay and setNeedsLayout will also wait until the run loop completes.

How do I get the view to display immediately?

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1 Answer

  1. Editorial Team

    Redrawing only occurs when your code returns control to the run loop. So the easiest way would be for you to schedule the startComputing call with a zero delay. That way, it will be executed during the next run loop iteration (right after redrawing):

    [computation performSelector:@selector(startComputing) withObject:nil afterDelay:0.0];

    Be aware, though, that unless you do your computation in another thread you will not be able to update the UI during the computation.

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