Added contains and clear implementations for iOS Settings

src/iOS.Core/Services/Settings.cs

@@ -1,5 +1,4 @@
-
-using System;
+using System;
 #if __UNIFIED__
 using Foundation;
 #else
@@ -230,6 +229,50 @@ namespace Bit.iOS.Core.Services
                 }
             }
         }
-    }
 
+        /// <summary>
+        /// Clear all keys from settings
+        /// </summary>
+        public void Clear()
+        {
+            lock(locker)
+            {
+                var defaults = _defaults;
+                try
+                {
+                    defaults.RemovePersistentDomain(NSBundle.MainBundle.BundleIdentifier);
+                    defaults.Synchronize();
+                }
+                catch(Exception ex)
+                {
+                    Console.WriteLine("Unable to clear all defaults. Message: " + ex.Message);
+                }
+            }
+        }
+
+        /// <summary>
+        /// Checks to see if the key has been added.
+        /// </summary>
+        /// <param name="key">Key to check</param>
+        /// <returns>True if contains key, else false</returns>
+        public bool Contains(string key)
+        {
+            lock(locker)
+            {
+                var defaults = _defaults;
+                try
+                {
+                    var nsString = new NSString(key);
+                    var setting = defaults.ValueForKey(nsString);
+                    return setting != null;
+                }
+                catch(Exception ex)
+                {
+                    Console.WriteLine("Unable to clear all defaults. Message: " + ex.Message);
+                }
+
+                return false;
+            }
+        }
+    }
 }