Added test and fixed implementation.

src/Perspex.Controls/TopLevel.cs

@@ -114,7 +114,7 @@ namespace Perspex.Controls
                 .Select(
                     x => (x as InputElement)?.GetObservable(CursorProperty) ?? Observable.Empty<Cursor>())
                 .Switch().Subscribe(cursor => PlatformImpl.SetCursor(cursor?.PlatformCursor));
-            _applicationLifecycle.OnExit += HandleApplicationExiting;
+            _applicationLifecycle.OnExit += OnApplicationExiting;
         }
 
         /// <summary>
@@ -355,7 +355,7 @@ namespace Perspex.Controls
 
         private void OnApplicationExiting(object sender, EventArgs args)
         {
-
+            HandleApplicationExiting();
         }
 
         /// <summary>

tests/Perspex.Controls.UnitTests/TopLevelTests.cs

@@ -282,12 +282,33 @@ namespace Perspex.Controls.UnitTests
                 });
         }
 
+        [Fact]
+        public void Exiting_Application_Notifies_Top_Level()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var impl = new Mock<ITopLevelImpl>();
+                impl.SetupAllProperties();
+                var target = new TestTopLevel(impl.Object);
+                UnitTestApplication.Current.Exit();
+                Assert.True(target.IsClosed);
+            }
+        }
+
         private class TestTopLevel : TopLevel
         {
+            public bool IsClosed { get; private set; }
+
             public TestTopLevel(ITopLevelImpl impl)
                 : base(impl)
             {
             }
+
+            protected override void HandleApplicationExiting()
+            {
+                base.HandleApplicationExiting();
+                IsClosed = true;
+            }
         }
     }
 }

tests/Perspex.UnitTests/UnitTestApplication.cs

@@ -6,6 +6,7 @@ using Perspex.Input;
 using Perspex.Layout;
 using Perspex.Platform;
 using Perspex.Styling;
+using Perspex.Controls;
 
 namespace Perspex.UnitTests
 {
@@ -41,7 +42,8 @@ namespace Perspex.UnitTests
                 .Bind<IPlatformThreadingInterface>().ToConstant(Services.ThreadingInterface)
                 .Bind<IStandardCursorFactory>().ToConstant(Services.StandardCursorFactory)
                 .Bind<IStyler>().ToConstant(Services.Styler)
-                .Bind<IWindowingPlatform>().ToConstant(Services.WindowingPlatform);
+                .Bind<IWindowingPlatform>().ToConstant(Services.WindowingPlatform)
+                .Bind<IApplicationLifecycle>().ToConstant(this);
         }
     }
 }