Fixes iOS 11 issue

Author: s4cha

KeyboardLayoutGuide/KeyboardLayoutGuide/Keyboard+LayoutGuide.swift

@@ -8,6 +8,11 @@
 
 import UIKit
 
+private class Keyboard {
+    static let shared = Keyboard()
+    var currentHeight: CGFloat = 0
+}
+
 public extension UIView {
 
     private struct AssociatedKeys {
@@ -51,11 +56,21 @@ open class KeyboardLayoutGuide: UILayoutGuide {
         guard let view = owningView else {
             return
         }
-        NSLayoutConstraint.activate([
-            heightAnchor.constraint(equalToConstant: 0),
-            leftAnchor.constraint(equalTo: view.leftAnchor),
-            rightAnchor.constraint(equalTo: view.rightAnchor),
-            ])
+        
+        if #available(iOS 11.0, *) {
+            NSLayoutConstraint.activate([
+                heightAnchor.constraint(equalToConstant: Keyboard.shared.currentHeight),
+                leftAnchor.constraint(equalTo: view.leftAnchor),
+                rightAnchor.constraint(equalTo: view.rightAnchor),
+                ])
+        } else {
+            NSLayoutConstraint.activate([
+                heightAnchor.constraint(equalToConstant: 0),
+                leftAnchor.constraint(equalTo: view.leftAnchor),
+                rightAnchor.constraint(equalTo: view.rightAnchor),
+                ])
+        }
+        
         let viewBottomAnchor: NSLayoutYAxisAnchor
         if #available(iOS 11.0, *) {
             viewBottomAnchor = view.safeAreaLayoutGuide.bottomAnchor
@@ -73,6 +88,9 @@ open class KeyboardLayoutGuide: UILayoutGuide {
             }
             heightConstraint?.constant = height
             animate(note)
+            if #available(iOS 11.0, *) {
+                Keyboard.shared.currentHeight = height
+            }
         }
     }