title: why need to use NSObject?
body: <p>i am confused about that should i need to used <code>NSObject</code> to swift3 . if so please guide me also is it best practice to used <code>NSNumber</code> </p>
  
  <pre><code>class App: NSObject {
  
          var id: NSNumber?
          var name: String?
          var category: String?
          var imageName: String?
          var price: NSNumber?
  
          var screenshots: [String]?
          var desc: String?
          var appInformation: AnyObject?
  
         // override func setValue(_ value: Any?, forKey key: String) {
         //     if key == "description" {
         //         self.desc = value as? String
         //     } else {
         //         super.setValue(value, forKey: key)
         //     }
         // }
  
      }
  </code></pre>
  
  <p>Note : <em>could you tell me please why need to use NSObject ? what is the advantage ?</em></p>