More ExpressionObserver tests.

src/Markup/Perspex.Markup/Binding/ExpressionNode.cs

@@ -35,7 +35,7 @@ namespace Perspex.Markup.Binding
 
                 if (_target != null)
                 {
-                    Subscribe(_target);
+                    SubscribeAndUpdate(_target);
                 }
                 else
                 {
@@ -95,7 +95,7 @@ namespace Perspex.Markup.Binding
             }
         }
 
-        protected abstract void Subscribe(object target);
+        protected abstract void SubscribeAndUpdate(object target);
 
         protected abstract void Unsubscribe(object target);
 

src/Markup/Perspex.Markup/Binding/PropertyAccessorNode.cs

@@ -18,7 +18,7 @@ namespace Perspex.Markup.Binding
 
         public string PropertyName { get; }
 
-        protected override void Subscribe(object target)
+        protected override void SubscribeAndUpdate(object target)
         {
             var result = ExpressionValue.None;
 

tests/Perspex.Markup.UnitTests/Binding/ExpressionObserverTests.cs

@@ -63,66 +63,94 @@ namespace Perspex.Markup.UnitTests.Binding
         [Fact]
         public void Should_Track_End_Of_Property_Chain_Changing()
         {
-            var data = new Class1 { Class2 = new Class2 { Bar = "bar" } };
-            var target = new ExpressionObserver(data, "Class2.Bar");
+            var data = new Class1 { Next = new Class2 { Bar = "bar" } };
+            var target = new ExpressionObserver(data, "Next.Bar");
             var result = new List<object>();
 
             var sub = target.Subscribe(x => result.Add(x.Value));
-            data.Class2.Bar = "baz";
+            ((Class2)data.Next).Bar = "baz";
 
             Assert.Equal(new[] { "bar", "baz" }, result);
 
             sub.Dispose();
 
             Assert.Equal(0, data.SubscriptionCount);
-            Assert.Equal(0, data.Class2.SubscriptionCount);
+            Assert.Equal(0, data.Next.SubscriptionCount);
         }
 
         [Fact]
-        public void Should_Track_Middle_Of_Property_Chain_Changing()
+        public void Should_Track_Property_Chain_Changing()
         {
-            var data = new Class1 { Class2 = new Class2 { Bar = "bar" } };
-            var target = new ExpressionObserver(data, "Class2.Bar");
+            var data = new Class1 { Next = new Class2 { Bar = "bar" } };
+            var target = new ExpressionObserver(data, "Next.Bar");
             var result = new List<object>();
 
             var sub = target.Subscribe(x => result.Add(x.Value));
-            var old = data.Class2;
-            data.Class2 = new Class2 { Bar = "baz" };
+            var old = data.Next;
+            data.Next = new Class2 { Bar = "baz" };
 
             Assert.Equal(new[] { "bar", "baz" }, result);
 
             sub.Dispose();
 
             Assert.Equal(0, data.SubscriptionCount);
-            Assert.Equal(0, data.Class2.SubscriptionCount);
+            Assert.Equal(0, data.Next.SubscriptionCount);
             Assert.Equal(0, old.SubscriptionCount);
         }
 
         [Fact]
-        public void Should_Track_Middle_Of_Property_Chain_Breaking_Then_Mending()
+        public void Should_Track_Property_Chain_Breaking_With_Null_Then_Mending()
         {
-            var data = new Class1 { Class2 = new Class2 { Bar = "bar" } };
-            var target = new ExpressionObserver(data, "Class2.Bar");
+            var data = new Class1 { Next = new Class2 { Bar = "bar" } };
+            var target = new ExpressionObserver(data, "Next.Bar");
             var result = new List<object>();
 
             var sub = target.Subscribe(x => result.Add(x.Value));
-            var old = data.Class2;
-            data.Class2 = null;
-            data.Class2 = new Class2 { Bar = "baz" };
+            var old = data.Next;
+            data.Next = null;
+            data.Next = new Class2 { Bar = "baz" };
 
             Assert.Equal(new[] { "bar", null, "baz" }, result);
 
             sub.Dispose();
 
             Assert.Equal(0, data.SubscriptionCount);
-            Assert.Equal(0, data.Class2.SubscriptionCount);
+            Assert.Equal(0, data.Next.SubscriptionCount);
             Assert.Equal(0, old.SubscriptionCount);
         }
 
+        [Fact]
+        public void Should_Track_Property_Chain_Breaking_With_Object_Then_Mending()
+        {
+            var data = new Class1 { Next = new Class2 { Bar = "bar" } };
+            var target = new ExpressionObserver(data, "Next.Bar");
+            var result = new List<object>();
+
+            var sub = target.Subscribe(x => result.Add(x.Value));
+            var old = data.Next;
+            var breaking = new WithoutBar();
+            data.Next = breaking;
+            data.Next = new Class2 { Bar = "baz" };
+
+            Assert.Equal(new[] { "bar", null, "baz" }, result);
+
+            sub.Dispose();
+
+            Assert.Equal(0, data.SubscriptionCount);
+            Assert.Equal(0, data.Next.SubscriptionCount);
+            Assert.Equal(0, breaking.SubscriptionCount);
+            Assert.Equal(0, old.SubscriptionCount);
+        }
+
+        private interface INext
+        {
+            int SubscriptionCount { get; }
+        }
+
         private class Class1 : NotifyingBase
         {
             private string _foo;
-            private Class2 _class2;
+            private INext _next;
 
             public string Foo
             {
@@ -134,18 +162,18 @@ namespace Perspex.Markup.UnitTests.Binding
                 }
             }
 
-            public Class2 Class2
+            public INext Next
             {
-                get { return _class2; }
+                get { return _next; }
                 set
                 {
-                    _class2 = value;
-                    RaisePropertyChanged(nameof(Class2));
+                    _next = value;
+                    RaisePropertyChanged(nameof(Next));
                 }
             }
         }
 
-        private class Class2 : NotifyingBase
+        private class Class2 : NotifyingBase, INext
         {
             private string _bar;
 
@@ -159,5 +187,9 @@ namespace Perspex.Markup.UnitTests.Binding
                 }
             }
         }
+
+        private class WithoutBar : NotifyingBase, INext
+        {
+        }
     }
 }

tests/Perspex.Markup.UnitTests/Binding/NotifyingBase.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using System.ComponentModel;
+using System.Linq;
 
 namespace Perspex.Markup.UnitTests.Binding
 {
@@ -19,8 +20,11 @@ namespace Perspex.Markup.UnitTests.Binding
 
             remove
             {
-                _propertyChanged -= value;
-                --SubscriptionCount;
+                if (_propertyChanged?.GetInvocationList().Contains(value) == true)
+                {
+                    _propertyChanged -= value;
+                    --SubscriptionCount;
+                }
             }
         }
 

tests/Perspex.Markup.UnitTests/Perspex.Markup.UnitTests.csproj

@@ -74,6 +74,7 @@
   <ItemGroup>
     <Compile Include="Binding\ExpressionObserverTests.cs" />
     <Compile Include="Binding\ExpressionNodeBuilderTests.cs" />
+    <Compile Include="Binding\NotifyingBase.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
   </ItemGroup>
   <ItemGroup>