How can I prevent the display on an iOS device from dimming and turning off? [duplicate]

Add this line of code on your application delegate:

Objective-C:

[[UIApplication sharedApplication] setIdleTimerDisabled:YES];

Swift 2:

UIApplication.sharedApplication().idleTimerDisabled = true

Swift 3, 4 & 5:

UIApplication.shared.isIdleTimerDisabled = true

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