Swift Value transformer that returns true if the value is a non empty string or false otherwise

IsEmptyStringValueTransformer.swift

import Foundation

/// Value transformer that returns NSNumber(true) if the value is a non empty string or NSNumber(false) otherwise
@objc public class IsEmptyStringValueTransformer: ValueTransformer {

   // Public name to use in interface builder
   private static let name = NSValueTransformerName(rawValue: "IsEmptyStringValueTransformer")

   // Shared value transformer instance
   @objc static public var shared = ValueTransformer(forName: IsEmptyStringValueTransformer.name)

   /// Call to register the value transformer. Must be called at least ONCE during initialization of your code
   @objc static public func Register() {
      ValueTransformer.setValueTransformer(
         IsEmptyStringValueTransformer(),
         forName: IsEmptyStringValueTransformer.name)
   }

   @objc public override class func transformedValueClass() -> AnyClass {
      return NSNumber.self
   }

   @objc public override class func allowsReverseTransformation() -> Bool {
      return false
   }

   @objc public override func transformedValue(_ value: Any?) -> Any? {
      guard let str = value as? String else {
         // Unfortunately we cannot tell whether a nil value is of a certain
         // type.  So if it's nil, assume that its an empty string
         return true
      }
      return NSNumber(value: str.isEmpty)
   }
}

You must register this value transformer ONCE before using. Usually this is done the initialisation of your app (for example, in applicationDidFinishLaunching.

func applicationDidFinishLaunching(_: Notification) {
    IsEmptyStringValueTransformer.Register()
}

And use the name IsEmptyStringValueTransformer in Interface Builder (for example, to hide a text field if there's no content in it via bindings)