Add overridable CanClose() method to Screen - meaning they don't have to use Tasks

Stylet/Screen.cs

@@ -220,10 +220,20 @@ namespace Stylet
         /// <summary>
         /// Called when a conductor wants to know whether this screen can close.
         /// </summary>
+        /// <remarks>Internally, this calls CanClose, and wraps the response in a Task</remarks>
         /// <returns>A task returning true (can close) or false (can't close)</returns>
         public virtual Task<bool> CanCloseAsync()
         {
-            return Task.FromResult(true);
+            return Task.FromResult(this.CanClose());
+        }
+
+        /// <summary>
+        /// Synchronous alternative to CanClose
+        /// </summary>
+        /// <returns>True if this screen can close, or false otherwise</returns>
+        protected virtual bool CanClose()
+        {
+            return true; 
         }
 
         #endregion

StyletUnitTests/ScreenTests.cs

@@ -55,6 +55,12 @@ namespace StyletUnitTests
             {
                 this.OnViewLoadedCalled = true;
             }
+
+            public bool? CanCloseResult = null;
+            protected override bool CanClose()
+            {
+                return this.CanCloseResult == null ? base.CanClose() : this.CanCloseResult.Value;
+            }
         }
 
         private MyScreen screen;
@@ -248,13 +254,22 @@ namespace StyletUnitTests
         }
 
         [Test]
-        public void CanCloseAsyncReturnsCompletedTrueTask()
+        public void CanCloseAsyncReturnsTrueByDefault()
         {
             var task = this.screen.CanCloseAsync();
             Assert.IsTrue(task.IsCompleted);
             Assert.IsTrue(task.Result);
         }
 
+        [Test]
+        public void CanCloseAsyncReturnsResultOfCanClose()
+        {
+            this.screen.CanCloseResult = false;
+            var task = this.screen.CanCloseAsync();
+            Assert.IsTrue(task.IsCompleted);
+            Assert.IsFalse(task.Result);
+        }
+
         [Test]
         public void TryCloseThrowsIfParentIsNotIChildDelegate()
         {