Give PriorityLevel a reference to its PriorityValue.

And directly call the LevelValueChanged method on it rather than using callbacks.

src/Perspex.Base/PriorityLevel.cs

@@ -31,34 +31,22 @@ namespace Perspex
     /// </remarks>
     internal class PriorityLevel
     {
-        /// <summary>
+        private PriorityValue _owner;
-        /// Method called when current value changes.
-        /// </summary>
-        private readonly Action<PriorityLevel> _changed;
-
-        /// <summary>
-        /// The current direct value.
-        /// </summary>
         private object _directValue;
-
-        /// <summary>
-        /// The index of the next <see cref="PriorityBindingEntry"/>.
-        /// </summary>
         private int _nextIndex;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="PriorityLevel"/> class.
         /// </summary>
+        /// <param name="owner">The owner.</param>
         /// <param name="priority">The priority.</param>
-        /// <param name="mode">The precedence mode.</param>
-        /// <param name="changed">A method to be called when the current value changes.</param>
         public PriorityLevel(
-            int priority,
+            PriorityValue owner,
-            Action<PriorityLevel> changed)
+            int priority)
         {
-            Contract.Requires<ArgumentNullException>(changed != null);
+            Contract.Requires<ArgumentNullException>(owner != null);
 
-            _changed = changed;
+            _owner = owner;
             Priority = priority;
             Value = _directValue = PerspexProperty.UnsetValue;
             ActiveBindingIndex = -1;
@@ -83,7 +71,7 @@ namespace Perspex
             set
             {
                 Value = _directValue = value;
-                _changed(this);
+                _owner.LevelValueChanged(this);
             }
         }
 
@@ -141,7 +129,7 @@ namespace Perspex
                 {
                     Value = entry.Value;
                     ActiveBindingIndex = entry.Index;
-                    _changed(this);
+                    _owner.LevelValueChanged(this);
                 }
                 else
                 {
@@ -175,14 +163,14 @@ namespace Perspex
                 {
                     Value = binding.Value;
                     ActiveBindingIndex = binding.Index;
-                    _changed(this);
+                    _owner.LevelValueChanged(this);
                     return;
                 }
             }
 
             Value = DirectValue;
             ActiveBindingIndex = -1;
-            _changed(this);
+            _owner.LevelValueChanged(this);
         }
     }
 }

src/Perspex.Base/PriorityValue.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using System.Reactive.Subjects;
 using System.Text;
 using Perspex.Logging;
 using Perspex.Utilities;
@@ -21,34 +20,15 @@ namespace Perspex
     /// priority binding that doesn't return <see cref="PerspexProperty.UnsetValue"/>. Where there
     /// are multiple bindings registered with the same priority, the most recently added binding
     /// has a higher priority. Each time the value changes, the 
-    /// <see cref="IPriorityValueOwner.Changed(PerspexProperty, object, object)"/> method on the 
+    /// <see cref="IPriorityValueOwner.Changed(PriorityValue, object, object)"/> method on the 
     /// owner object is fired with the old and new values.
     /// </remarks>
     internal class PriorityValue
     {
-        /// <summary>
-        /// The owner of the object.
-        /// </summary>
         private readonly IPriorityValueOwner _owner;
-
-        /// <summary>
-        /// The value type.
-        /// </summary>
         private readonly Type _valueType;
-
-        /// <summary>
-        /// The currently registered bindings organised by priority.
-        /// </summary>
         private readonly Dictionary<int, PriorityLevel> _levels = new Dictionary<int, PriorityLevel>();
-
-        /// <summary>
-        /// The current value.
-        /// </summary>
         private object _value;
-
-        /// <summary>
-        /// The function used to validate the value, if any.
-        /// </summary>
         private readonly Func<object, object> _validate;
 
         /// <summary>
@@ -169,6 +149,34 @@ namespace Perspex
             return b.ToString();
         }
 
+        /// <summary>
+        /// Called when the value for a priority level changes.
+        /// </summary>
+        /// <param name="level">The priority level of the changed entry.</param>
+        public void LevelValueChanged(PriorityLevel level)
+        {
+            if (level.Priority <= ValuePriority)
+            {
+                if (level.Value != PerspexProperty.UnsetValue)
+                {
+                    UpdateValue(level.Value, level.Priority);
+                }
+                else
+                {
+                    foreach (var i in _levels.Values.OrderBy(x => x.Priority))
+                    {
+                        if (i.Value != PerspexProperty.UnsetValue)
+                        {
+                            UpdateValue(i.Value, i.Priority);
+                            return;
+                        }
+                    }
+
+                    UpdateValue(PerspexProperty.UnsetValue, int.MaxValue);
+                }
+            }
+        }
+
         /// <summary>
         /// Causes a revalidation of the value.
         /// </summary>
@@ -197,7 +205,7 @@ namespace Perspex
 
             if (!_levels.TryGetValue(priority, out result))
             {
-                result = new PriorityLevel(priority, ValueChanged);
+                result = new PriorityLevel(this, priority);
                 _levels.Add(priority, result);
             }
 
@@ -238,33 +246,5 @@ namespace Perspex
                     value.GetType());
             }
         }
-
-        /// <summary>
-        /// Called when the value for a priority level changes.
-        /// </summary>
-        /// <param name="level">The priority level of the changed entry.</param>
-        private void ValueChanged(PriorityLevel level)
-        {
-            if (level.Priority <= ValuePriority)
-            {
-                if (level.Value != PerspexProperty.UnsetValue)
-                {
-                    UpdateValue(level.Value, level.Priority);
-                }
-                else
-                {
-                    foreach (var i in _levels.Values.OrderBy(x => x.Priority))
-                    {
-                        if (i.Value != PerspexProperty.UnsetValue)
-                        {
-                            UpdateValue(i.Value, i.Priority);
-                            return;
-                        }
-                    }
-
-                    UpdateValue(PerspexProperty.UnsetValue, int.MaxValue);
-                }
-            }
-        }
     }
 }