Add a cancel button to passcode lock of app extension

passKit/Helpers/UIViewExtension.swift

@@ -0,0 +1,45 @@
+//
+//  UIViewExtension.swift
+//  passKit
+//
+//  Created by Yishi Lin on 2018/4/11.
+//  Copyright © 2018 Yishi Lin. All rights reserved.
+//
+
+import Foundation
+
+extension UIView {
+    
+    // Save anchors: https://stackoverflow.com/questions/46317061/use-safe-area-layout-programmatically
+    var safeTopAnchor: NSLayoutYAxisAnchor {
+        if #available(iOS 11.0, *) {
+            return self.safeAreaLayoutGuide.topAnchor
+        } else {
+            return self.topAnchor
+        }
+    }
+    
+    var safeLeftAnchor: NSLayoutXAxisAnchor {
+        if #available(iOS 11.0, *){
+            return self.safeAreaLayoutGuide.leftAnchor
+        } else {
+            return self.leftAnchor
+        }
+    }
+    
+    var safeRightAnchor: NSLayoutXAxisAnchor {
+        if #available(iOS 11.0, *){
+            return self.safeAreaLayoutGuide.rightAnchor
+        } else {
+            return self.rightAnchor
+        }
+    }
+    
+    var safeBottomAnchor: NSLayoutYAxisAnchor {
+        if #available(iOS 11.0, *) {
+            return self.safeAreaLayoutGuide.bottomAnchor
+        } else {
+            return self.bottomAnchor
+        }
+    }
+}