Adds a mechanism in PredefinedValues to allow handle separator string values

Xamarin.PropertyEditing.Mac/Controls/PredefinedValuesEditor.cs

@@ -39,14 +39,22 @@ protected override void OnViewModelChanged (PropertyViewModel oldModel)
 
 				this.popupButtonList.RemoveAllItems ();
 				foreach (var item in ViewModel.PossibleValues) {
-					this.popupButtonList.AddItem (new NSMenuItem (item));
+					if (!string.IsNullOrEmpty (ViewModel.SeparatorString) && ViewModel.SeparatorString == item) {
+						this.popupButtonList.AddItem (NSMenuItem.SeparatorItem);
+					} else {
+						this.popupButtonList.AddItem (new NSMenuItem (item));
+					}
 				}
 			} else {
 				RequireComboBox ();
 
 				this.comboBox.RemoveAll ();
 				foreach (var item in ViewModel.PossibleValues) {
-					this.comboBox.Add (new NSString (item));
+					if (!string.IsNullOrEmpty (ViewModel.SeparatorString) && ViewModel.SeparatorString == item) {
+						this.comboBox.Add (NSMenuItem.SeparatorItem);
+					} else {
+						this.comboBox.Add (new NSString (item));
+					}
 				}
 			}
 

Xamarin.PropertyEditing/IHavePredefinedValues.cs

@@ -21,6 +21,8 @@ public interface IHavePredefinedValues<TValue>
 		/// </remarks>
 		bool IsValueCombinable { get; }
 
+		string SeparatorString { get; }
+
 		IReadOnlyDictionary<string, TValue> PredefinedValues { get; }
 	}
 }

Xamarin.PropertyEditing/Reflection/ReflectionEnumPropertyInfo.cs

@@ -44,6 +44,8 @@ public IReadOnlyDictionary<string, T> PredefinedValues
 			get;
 		}
 
+		public string SeparatorString { get; }
+
 #pragma warning disable CS1998 // Async method lacks 'await' operators and will run synchronously
 		public override async Task SetValueAsync<TValue> (object target, TValue value)
 		{

Xamarin.PropertyEditing/ViewModels/PredefinedValuesViewModel.cs

@@ -41,6 +41,8 @@ public string ValueName
 			set { SetValueName (value); }
 		}
 
+		public string SeparatorString => this.predefinedValues.SeparatorString;
+
 		public bool IsConstrainedToPredefined => this.predefinedValues.IsConstrainedToPredefined;
 
 		protected override TValue CoerceValue (TValue validationValue)