Execute.Dispatcher can never be null, and dispatches synchronously by default

The previous behaviour was to raise an exception unless Execute.Dispatcher
had been explicitly defined. This was to detect cases where the user hadn't
set up Execute correctly, and treat them as errors rather than simply going
ahead with some possibly-unexpected behaviour.

However, since BootstrapperBase sets Execute.Dispatcher automatically, it's
highly unlikely that itwould ever not be set when it needed to be. Exceptions
are design mode and unit tests, both of which want (or can cope with) a
synchronous dispatcher.

Hence the behaviour change. Execute.Dispatcher is a synchronous dispatcher
by default, but is overridden to one that uses Application.Current.Dispatcher
by the bootstrapper if we're in a real application.

Stylet/BootstrapperBase.cs

@@ -47,10 +47,7 @@ namespace Stylet
         {
             this.Application = application;
 
-            this.Application.Startup += (o, e) =>
-            {
-                this.Start(e.Args);
-            };
+            this.Application.Startup += (o, e) => this.Start(e.Args);
 
             // Make life nice for the app - they can handle these by overriding Bootstrapper methods, rather than adding event handlers
             this.Application.Exit += (o, e) => this.OnExit(e);
@@ -69,7 +66,7 @@ namespace Stylet
             this.Args = args;
 
             // Use the current SynchronizationContext for the Execute helper
-            Execute.Dispatcher = new DispatcherWrapper(Dispatcher.CurrentDispatcher);
+            Execute.Dispatcher = new DispatcherWrapper(this.Application.Dispatcher);
 
             this.ConfigureBootstrapper();
 

Stylet/Execute.cs

@@ -52,15 +52,50 @@ namespace Stylet
         }
     }
 
+    internal class SynchronousDispatcher : IDispatcher
+    {
+        public void Post(Action action)
+        {
+            action();
+        }
+
+        public void Send(Action action)
+        {
+            action();
+        }
+
+        public bool IsCurrent
+        {
+            get { return true; }
+        }
+    }
+
     /// <summary>
     /// Static class providing methods to easily run an action on the UI thread in various ways, and some other things
     /// </summary>
     public static class Execute
     {
+        private static IDispatcher _dispatcher;
+
         /// <summary>
         /// Should be set to the UI thread's Dispatcher. This is normally done by the Bootstrapper.
         /// </summary>
-        public static IDispatcher Dispatcher { get; set; }
+        public static IDispatcher Dispatcher
+        {
+            get
+            {
+                if (_dispatcher == null)
+                    _dispatcher = new SynchronousDispatcher();
+                return _dispatcher;
+            }
+
+            set
+            {
+                if (value == null)
+                    throw new ArgumentNullException();
+                _dispatcher = value;
+            }
+        }
 
         private static bool? inDesignMode;
 
@@ -74,19 +109,12 @@ namespace Stylet
         /// </summary>
         public static Action<Action> DefaultCollectionChangedDispatcher = Execute.OnUIThreadSync;
 
-        private static void EnsureDispatcher()
-        {
-            if (Dispatcher == null)
-                throw new InvalidOperationException("Execute.Dispatcher must be set before this method can be called. This should normally have been done by the Bootstrapper");
-        }
-
         /// <summary>
         /// Dispatches the given action to be run on the UI thread asynchronously, even if the current thread is the UI thread
         /// </summary>
         /// <param name="action">Action to run on the UI thread</param>
         public static void PostToUIThread(Action action)
         {
-            EnsureDispatcher();
             Dispatcher.Post(action);
         }
 
@@ -98,7 +126,6 @@ namespace Stylet
         /// <returns>Task which completes when the action has been run</returns>
         public static Task PostToUIThreadAsync(Action action)
         {
-            EnsureDispatcher();
             return PostOnUIThreadInternalAsync(action);
         }
 
@@ -108,7 +135,6 @@ namespace Stylet
         /// <param name="action">Action to run on the UI thread</param>
         public static void OnUIThread(Action action)
         {
-            EnsureDispatcher();
             if (Dispatcher.IsCurrent)
                 action();
             else
@@ -121,7 +147,6 @@ namespace Stylet
         /// <param name="action">Action to run on the UI thread</param>
         public static void OnUIThreadSync(Action action)
         {
-            EnsureDispatcher();
             Exception exception = null;
             if (Dispatcher.IsCurrent)
             {
@@ -153,7 +178,6 @@ namespace Stylet
         /// <returns>Task which completes when the action has been run</returns>
         public static Task OnUIThreadAsync(Action action)
         {
-            EnsureDispatcher();
             if (Dispatcher.IsCurrent)
             {
                 action();

StyletUnitTests/BindableCollectionTests.cs

@@ -16,12 +16,6 @@ namespace StyletUnitTests
     {
         private class Element { }
 
-        [TestFixtureSetUp]
-        public void SetUpFixture()
-        {
-            Execute.Dispatcher = new SynchronousDispatcher();
-        }
-
         [Test]
         public void AddRangeAddsElements()
         {

StyletUnitTests/BootstrapperBaseTests.cs

@@ -73,31 +73,52 @@ namespace StyletUnitTests
             }
         }
 
+        private class FakeDispatcher : IDispatcher
+        {
+            public void Post(Action action)
+            {
+                throw new NotImplementedException();
+            }
+
+            public void Send(Action action)
+            {
+                throw new NotImplementedException();
+            }
+
+            public bool IsCurrent
+            {
+                get { throw new NotImplementedException(); }
+            }
+        }
+
         
         private MyBootstrapperBase<RootViewModel> bootstrapper;
         private Mock<IViewManager> viewManager;
         private Mock<IWindowManager> windowManager;
 
-        [TestFixtureSetUp]
-        public void FixtureSetUp()
-        {
-            Execute.Dispatcher = new SynchronousDispatcher();
-        }
+        private IDispatcher dispatcher;
 
         [SetUp]
         public void SetUp()
         {
+            this.dispatcher = Execute.Dispatcher;
             this.viewManager = new Mock<IViewManager>();
             this.windowManager = new Mock<IWindowManager>();
             this.bootstrapper = new MyBootstrapperBase<RootViewModel>(this.viewManager.Object, this.windowManager.Object);
         }
 
+        [TearDown]
+        public void TearDown()
+        {
+            Execute.Dispatcher = this.dispatcher;
+        }
+
         [Test]
         public void StartAssignsExecuteDispatcher()
         {
-            Execute.Dispatcher = null;
+            Execute.Dispatcher = new FakeDispatcher();
             this.bootstrapper.Start(new string[0]);
-            Assert.NotNull(Execute.Dispatcher); // Can't test any further, unfortunately
+            Assert.IsNotInstanceOf<FakeDispatcher>(Execute.Dispatcher); // Can't test any further, unfortunately
         }
 
         [Test]

StyletUnitTests/BootstrapperTests.cs

@@ -43,12 +43,6 @@ namespace StyletUnitTests
 
         private MyBootstrapper<RootViewModel> bootstrapper;
 
-        [TestFixtureSetUp]
-        public void FixtureSetUp()
-        {
-            Execute.Dispatcher = new SynchronousDispatcher();
-        }
-
         [SetUp]
         public void SetUp()
         {

StyletUnitTests/CommandActionTests.cs

@@ -55,12 +55,6 @@ namespace StyletUnitTests
         private DependencyObject subject;
         private Target target;
 
-        [TestFixtureSetUp]
-        public void TestFixtureSetUp()
-        {
-            Execute.Dispatcher = new SynchronousDispatcher();
-        }
-
         [SetUp]
         public void SetUp()
         {

StyletUnitTests/ConductorAllActiveTests.cs

@@ -17,12 +17,6 @@ namespace StyletUnitTests
 
         private Conductor<IScreen>.Collection.AllActive conductor;
 
-        [TestFixtureSetUp]
-        public void SetUpFixture()
-        {
-            Execute.Dispatcher = new SynchronousDispatcher();
-        }
-
         [SetUp]
         public void SetUp()
         {

StyletUnitTests/ConductorOneActiveTests.cs

@@ -17,12 +17,6 @@ namespace StyletUnitTests
 
         private Conductor<IScreen>.Collection.OneActive conductor;
 
-        [TestFixtureSetUp]
-        public void SetUpFixture()
-        {
-            Execute.Dispatcher = new SynchronousDispatcher();
-        }
-
         [SetUp]
         public void SetUp()
         {

StyletUnitTests/EventActionTests.cs

@@ -46,12 +46,6 @@ namespace StyletUnitTests
         private Target target;
         private EventInfo eventInfo;
 
-        [TestFixtureSetUp]
-        public void TestFixtureSetUp()
-        {
-            Execute.Dispatcher = new SynchronousDispatcher();
-        }
-
         [SetUp]
         public void SetUp()
         {

StyletUnitTests/EventAggregatorTests.cs

@@ -36,12 +36,6 @@ namespace StyletUnitTests
 
         private EventAggregator ea;
 
-        [TestFixtureSetUp]
-        public void SetUpFixture()
-        {
-            Execute.Dispatcher = new SynchronousDispatcher();
-        }
-
         [SetUp]
         public void SetUp()
         {

StyletUnitTests/ExecuteTests.cs

@@ -13,11 +13,18 @@ namespace StyletUnitTests
     [TestFixture]
     public class ExecuteTests
     {
+        private IDispatcher dispatcher;
+
         [SetUp]
         public void SetUp()
         {
-            // Dont want this being previously set by anything and messing us around
-            Execute.Dispatcher = new SynchronousDispatcher();
+            this.dispatcher = Execute.Dispatcher;
+        }
+
+        [TearDown]
+        public void TearDown()
+        {
+            Execute.Dispatcher = this.dispatcher;
         }
 
         [Test]
@@ -205,38 +212,25 @@ namespace StyletUnitTests
         }
 
         [Test]
-        public void ThrowsIfPostToUIThreadCalledWithNoDispatcher()
+        public void ThrowsIfDispatcherSetToNull()
         {
-            Execute.Dispatcher = null;
-            Assert.Throws<InvalidOperationException>(() => Execute.PostToUIThread(() => { }));
+            Assert.Throws<ArgumentNullException>(() => Execute.Dispatcher = null);
         }
 
         [Test]
-        public void ThrowsIfPostToUIThreadAsyncCalledWithNoDispatcher()
+        public void DefaultDispatcherIsSynchronous()
         {
-            Execute.Dispatcher = null;
-            Assert.Throws<InvalidOperationException>(() => Execute.PostToUIThreadAsync(() => { }));
-        }
+            var dispatcher = Execute.Dispatcher;
 
-        [Test]
-        public void ThrowsIfOnUIThreadCalledWithNoDispatcher()
-        {
-            Execute.Dispatcher = null;
-            Assert.Throws<InvalidOperationException>(() => Execute.OnUIThread(() => { }));
-        }
+            Assert.IsTrue(dispatcher.IsCurrent);
 
-        [Test]
-        public void ThrowsIfOnUIThreadSyncCalledWithNoDispatcher()
-        {
-            Execute.Dispatcher = null;
-            Assert.Throws<InvalidOperationException>(() => Execute.OnUIThreadSync(() => { }));
-        }
+            bool actionCalled = false;
+            dispatcher.Post(() => actionCalled = true);
+            Assert.IsTrue(actionCalled);
 
-        [Test]
-        public void ThrowsIfOnUIThreadAsyncCalledWithNoDispatcher()
-        {
-            Execute.Dispatcher = null;
-            Assert.Throws<InvalidOperationException>(() => Execute.OnUIThreadAsync(() => { }));
+            actionCalled = false;
+            dispatcher.Send(() => actionCalled = true);
+            Assert.IsTrue(actionCalled);
         }
 
         [Test]

StyletUnitTests/PropertyChangedBaseTests.cs

@@ -34,12 +34,6 @@ namespace StyletUnitTests
             }
         }
 
-        [TestFixtureSetUp]
-        public void SetUpFixture()
-        {
-            Execute.Dispatcher = new SynchronousDispatcher();
-        }
-
         [Test]
         public void RefreshRaisesPropertyChangedWithEmptyString()
         {

StyletUnitTests/PropertyChangedExtensionsTests.cs

@@ -52,12 +52,6 @@ namespace StyletUnitTests
         private string newVal;
         private object sender;
 
-        [TestFixtureSetUp]
-        public void SetUpFixture()
-        {
-            Execute.Dispatcher = new SynchronousDispatcher();
-        }
-
         [SetUp]
         public void SetUp()
         {

StyletUnitTests/ScreenTests.cs

@@ -65,13 +65,6 @@ namespace StyletUnitTests
 
         private MyScreen screen;
 
-        [TestFixtureSetUp]
-        public void SetUpFixture()
-        {
-            Execute.Dispatcher = new SynchronousDispatcher();
-        }
-
-
         [SetUp]
         public void SetUp()
         {

StyletUnitTests/StyletUnitTests.csproj

@@ -67,7 +67,6 @@
     <Compile Include="StyletIoC\StyletIoCFuncFactoryTests.cs" />
     <Compile Include="StyletIoC\StyletIoCInstanceBindingTests.cs" />
     <Compile Include="StyletIoC\StyletIoCModuleTests.cs" />
-    <Compile Include="SynchronousDispatcher.cs" />
     <Compile Include="TraceLoggerTests.cs" />
     <Compile Include="EqualityConverterTests.cs" />
     <Compile Include="EventActionTests.cs" />

StyletUnitTests/SynchronousDispatcher.cs

@@ -1,27 +0,0 @@
-using Stylet;
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-
-namespace StyletUnitTests
-{
-    internal class SynchronousDispatcher : IDispatcher
-    {
-        public void Post(Action action)
-        {
-            throw new InvalidOperationException();
-        }
-
-        public void Send(Action action)
-        {
-            throw new InvalidOperationException();
-        }
-
-        public bool IsCurrent
-        {
-            get { return true; }
-        }
-    }
-}

StyletUnitTests/ValidatingModelBaseTests.cs

@@ -71,12 +71,6 @@ namespace StyletUnitTests
         private Mock<IModelValidator> validator;
         private MyModel model;
 
-        [TestFixtureSetUp]
-        public void SetUpFixture()
-        {
-            Execute.Dispatcher = new SynchronousDispatcher();
-        }
-
         [SetUp]
         public void SetUp()
         {

StyletUnitTests/ViewManagerTests.cs

@@ -104,12 +104,6 @@ namespace StyletUnitTests
 
         private AccessibleViewManager viewManager;
 
-        [TestFixtureSetUp]
-        public void FixtureSetUp()
-        {
-            Execute.Dispatcher = new SynchronousDispatcher();
-        }
-
         [SetUp]
         public void SetUp()
         {
@@ -186,7 +180,6 @@ namespace StyletUnitTests
             var config = new Mock<IViewManagerConfig>();
             config.SetupGet(x => x.Assemblies).Returns(new List<Assembly>() { Assembly.GetExecutingAssembly() });
             var viewManager = new AccessibleViewManager(config.Object);
-            Execute.Dispatcher = new SynchronousDispatcher();
             var viewType = viewManager.LocateViewForModel(typeof(ViewManagerTestsViewModel));
             Assert.AreEqual(typeof(ViewManagerTestsView), viewType);
         }