Using “next" as a return key

- Usage: set delegate and nextField of textField (storyboard or code)

pass/Helpers/UITextFieldExtension.swift

@@ -0,0 +1,34 @@
+//
+//  UIViewControllerExtionsion.swift
+//  pass
+//
+//  Created by Yishi Lin on 5/4/17.
+//  Copyright © 2017 Yishi Lin. All rights reserved.
+//
+
+import Foundation
+import UIKit
+
+private var kAssociationKeyNextField: UInt8 = 0
+
+extension UITextField {
+    @IBOutlet var nextField: UITextField? {
+        get {
+            return objc_getAssociatedObject(self, &kAssociationKeyNextField) as? UITextField
+        }
+        set(newField) {
+            objc_setAssociatedObject(self, &kAssociationKeyNextField, newField, .OBJC_ASSOCIATION_RETAIN)
+        }
+    }
+}
+
+extension UIViewController {
+    func textFieldShouldReturn(_ textField: UITextField) -> Bool {
+        if textField.nextField != nil {
+            textField.nextField?.becomeFirstResponder()
+        } else {
+            textField.resignFirstResponder()
+        }
+        return true
+    }
+}