Adding concurrency to an existing app with GCD

…In this example, I'm going to use grand central…dispatch together with blocks to take an application that has…major UI responsiveness issues and fix them by running…some tasks concurrently with just a few lines of code.…So right now, I have this simlpe application.…It's got a date picker on there.…It's got a segmented control.…There's a button here that says Long-Running Operation.…And if I touch the button, the UI's going to…totally lock up for a few moments while it goes and…does something in the background, before it…finally comes back and updates the screen.…

Just doing that again, I'm going to start spinning a…couple of these wheels, hit the button, they immediately lock,…I cannot even click the segmented control, until this comes…back from doing whatever it was doing a moment ago.…This might be fetching some data, internally creating some complex…objects, performing a long calculation, whatever that needs to do.…So, this is not good behavior. Your users aren't going to like it.…It doesn't feel professional.…