iOS Label Text Change with sleep()

Question

I found interesting things.. Following code doesn't show @"One" and it show @"Two" after 3 seconds delay.. I think that @"One" need to be shown and then 3 seconds delay and then @"Two" need to pop up.. Am I wrong?

self.statusLabel.text = @"One";
sleep(3);
self.statusLabel.text = @"Two";

Thanks..

Answer 1

If you're doing this on the main thread, that sleep(3) will block it, freezing the app for 3 seconds. Event processing, including things like repainting the UI, won't happen til that's over.

To get what you're expecting, try something like this:

[self.statusLabel setText:@"One"];
[self.statusLabel performSelector:@selector(setText:)
                       withObject:@"Two"
                       afterDelay:3.0];

Does the first change, then queues up an invocation performing the second change to happen in the future. Then returns control to the OS to do any necessary redrawing.