Updated ActivatedSubject.

Can be expressed more cleanly given the new `ActivatedObject`.

src/Avalonia.Styling/Styling/ActivatedObservable.cs

@@ -24,8 +24,6 @@ namespace Avalonia.Styling
         private List<IObserver<object>> _observers;
         private IDisposable _activatorSubscription;
         private IDisposable _sourceSubscription;
-        private bool? _active;
-        private object _value;
         private object _last = NotSent;
 
         /// <summary>
@@ -58,11 +56,21 @@ namespace Avalonia.Styling
         /// </summary>
         public string Description { get; }
 
+        /// <summary>
+        /// Gets a value indicating whether the observable is active.
+        /// </summary>
+        public bool? IsActive { get; private set; }
+
         /// <summary>
         /// Gets an observable which produces the <see cref="ActivatedValue"/>.
         /// </summary>
         public IObservable<object> Source { get; }
 
+        /// <summary>
+        /// Gets the value that will be produced when <see cref="IsActive"/> is true.
+        /// </summary>
+        public object Value { get; private set; }
+
         public IDisposable Subscribe(IObserver<object> observer)
         {
             var subscribe = _observers == null;
@@ -90,7 +98,7 @@ namespace Avalonia.Styling
             });
         }
 
-        private void NotifyCompleted()
+        protected virtual void NotifyCompleted()
         {
             foreach (var observer in _observers)
             {
@@ -100,7 +108,7 @@ namespace Avalonia.Styling
             _observers = null;
         }
 
-        private void NotifyError(Exception error)
+        protected virtual void NotifyError(Exception error)
         {
             foreach (var observer in _observers)
             {
@@ -110,11 +118,23 @@ namespace Avalonia.Styling
             _observers = null;
         }
 
+        protected virtual void NotifyValue(object value)
+        {
+            Value = value;
+            Update();
+        }
+
+        protected virtual void NotifyActive(bool active)
+        {
+            IsActive = active;
+            Update();
+        }
+
         private void Update()
         {
-            if (_active.HasValue)
+            if (IsActive.HasValue)
             {
-                var v = _active.Value ? _value : AvaloniaProperty.UnsetValue;
+                var v = IsActive.Value ? Value : AvaloniaProperty.UnsetValue;
 
                 if (!Equals(v, _last))
                 {
@@ -141,18 +161,8 @@ namespace Avalonia.Styling
             void IObserver<object>.OnCompleted() => _parent.NotifyCompleted();
             void IObserver<bool>.OnError(Exception error) => _parent.NotifyError(error);
             void IObserver<object>.OnError(Exception error) => _parent.NotifyError(error);
-
-            void IObserver<bool>.OnNext(bool value)
-            {
-                _parent._active = value;
-                _parent.Update();
-            }
-
-            void IObserver<object>.OnNext(object value)
-            {
-                _parent._value = value;
-                _parent.Update();
-            }
+            void IObserver<bool>.OnNext(bool value) => _parent.NotifyActive(value);
+            void IObserver<object>.OnNext(object value) => _parent.NotifyValue(value);
         }
     }
 }

src/Avalonia.Styling/Styling/ActivatedSubject.cs

@@ -2,7 +2,6 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using System;
-using System.Reactive.Linq;
 using System.Reactive.Subjects;
 
 namespace Avalonia.Styling
@@ -19,9 +18,8 @@ namespace Avalonia.Styling
     /// </remarks>
     internal class ActivatedSubject : ActivatedObservable, ISubject<object>, IDescription
     {
-        private bool? _active;
         private bool _completed;
-        private object _value;
+        private object _pushValue;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ActivatedSubject"/> class.
@@ -35,7 +33,6 @@ namespace Avalonia.Styling
             string description)
             : base(activator, source, description)
         {
-            Activator.Subscribe(ActivatorChanged, ActivatorError, ActivatorCompleted);
         }
 
         /// <summary>
@@ -46,53 +43,57 @@ namespace Avalonia.Styling
             get { return (ISubject<object>)base.Source; }
         }
 
-        /// <summary>
-        /// Notifies all subscribed observers about the end of the sequence.
-        /// </summary>
         public void OnCompleted()
         {
-            if (_active.Value && !_completed)
+            Source.OnCompleted();
+        }
+
+        public void OnError(Exception error)
+        {
+            Source.OnError(error);
+        }
+
+        public void OnNext(object value)
+        {
+            _pushValue = value;
+
+            if (IsActive == true && !_completed)
             {
-                Source.OnCompleted();
+                Source.OnNext(_pushValue);
             }
         }
 
-        /// <summary>
-        /// Notifies all subscribed observers with the exception.
-        /// </summary>
-        /// <param name="error">The exception to send to all subscribed observers.</param>
-        /// <exception cref="ArgumentNullException"><paramref name="error"/> is null.</exception>
-        public void OnError(Exception error)
+        protected override void NotifyCompleted()
         {
-            if (_active.Value && !_completed)
+            base.NotifyCompleted();
+
+            if (!_completed)
             {
-                Source.OnError(error);
+                Source.OnCompleted();
+                _completed = true;
             }
         }
 
-        /// <summary>
-        /// Notifies all subscribed observers with the value.
-        /// </summary>
-        /// <param name="value">The value to send to all subscribed observers.</param>        
-        public void OnNext(object value)
+        protected override void NotifyError(Exception error)
         {
-            _value = value;
+            base.NotifyError(error);
 
-            if (_active.Value && !_completed)
+            if (!_completed)
             {
-                Source.OnNext(value);
+                Source.OnError(error);
+                _completed = true;
             }
         }
 
-        private void ActivatorChanged(bool active)
+        protected override void NotifyActive(bool active)
         {
-            bool first = !_active.HasValue;
+            bool first = !IsActive.HasValue;
 
-            _active = active;
+            base.NotifyActive(active);
 
             if (!first)
             {
-                Source.OnNext(active ? _value : AvaloniaProperty.UnsetValue);
+                Source.OnNext(active ? _pushValue : AvaloniaProperty.UnsetValue);
             }
         }
 

tests/Avalonia.Styling.UnitTests/ActivatedSubjectTests.cs

@@ -17,6 +17,7 @@ namespace Avalonia.Styling.UnitTests
             var source = new TestSubject();
             var target = new ActivatedSubject(activator, source, string.Empty);
 
+            target.Subscribe();
             target.OnNext("bar");
             Assert.Equal(AvaloniaProperty.UnsetValue, source.Value);
             activator.OnNext(true);
@@ -36,6 +37,7 @@ namespace Avalonia.Styling.UnitTests
             var source = new TestSubject();
             var target = new ActivatedSubject(activator, source, string.Empty);
 
+            target.Subscribe();
             activator.OnCompleted();
 
             Assert.True(source.Completed);
@@ -47,10 +49,14 @@ namespace Avalonia.Styling.UnitTests
             var activator = new BehaviorSubject<bool>(false);
             var source = new TestSubject();
             var target = new ActivatedSubject(activator, source, string.Empty);
+            var targetError = default(Exception);
+            var error = new Exception();
 
-            activator.OnError(new Exception());
+            target.Subscribe(_ => { }, e => targetError = e);
+            activator.OnError(error);
 
-            Assert.NotNull(source.Error);
+            Assert.Same(error, source.Error);
+            Assert.Same(error, targetError);
         }
 
         private class TestSubject : ISubject<object>