How to prevent screen lock on my application with swift on iOS

Use this:

Objective-C:

[[UIApplication sharedApplication] setIdleTimerDisabled: YES];

Swift (legacy):

UIApplication.sharedApplication().idleTimerDisabled = true

Swift 3 and above:

UIApplication.shared.isIdleTimerDisabled = true

Make sure to import UIKit.

Here is the link to the documentation from developer.apple.com.