How do I prevent the iPhone screen from dimming or turning off while my application is running?

Question

Objective-C

[[UIApplication sharedApplication] setIdleTimerDisabled:YES];

Swift

UIApplication.shared.isIdleTimerDisabled = true

In swift you can use this as

UIApplication.sharedApplication().idleTimerDisabled = true

Swift 3:

UIApplication.shared.isIdleTimerDisabled = true

I have put this line of code in my view controller yet we still get customers saying the screen will dim or turn off until someone touches the screen. I have seen other posts where not only do you programatically set

UIApplication.sharedApplication().idleTimerDisabled = true 

to true but you must reset it to false first

UIApplication.sharedApplication().idleTimerDisabled = false
UIApplication.sharedApplication().idleTimerDisabled = true

Sadly this still did not work and customers are still getting dimmed screens. We have Apple Configurator profile preventing the device from going to sleep, and still some devices screen go dim and the customer needs to press the home button to wake the screen. I now put this code into a timer that fires every 2.5 hours to reset the idle timer, hopefully this will work.