How to get reference of AppDelegate
<p>My problem is i've constants class which is used in almost each classes in application so i've created its object in AppDelegate n through it want to access them.i don't want create object of constants every where each time.what will be the best approach please advice.</p>

<pre><code>class AppDelegate: UIResponder, UIApplicationDelegate {
 public var constants = Constants()
//created object once in app delegate
}

class Utility
{
let delegate = UIApplication.shared.delegate as! AppDelegate //getting     null here
let constants =  delegate. constants
}`
</code></pre>