Merge pull request #4790 from michael-hawker/llama/fix4505

TaskResultConverter returns default value when task not set

Author: michael-hawker

Microsoft.Toolkit.Uwp.UI/Converters/TaskResultConverter.cs

@@ -14,8 +14,8 @@ namespace Microsoft.Toolkit.Uwp.UI.Converters
     /// This is needed because accessing <see cref="Task{TResult}.Result"/> when the task has not
     /// completed yet will block the current thread and might cause a deadlock (eg. if the task was
     /// scheduled on the same synchronization context where the result is being retrieved from).
-    /// The methods in this converter will safely return <see langword="default"/> if the input
-    /// task is still running, or if it has faulted or has been canceled.
+    /// The methods in this converter will safely return <see langword="null"/> if the input
+    /// task is not set yet, still running, has faulted, or has been canceled.
     /// </summary>
     public sealed class TaskResultConverter : IValueConverter
     {
@@ -26,8 +26,13 @@ public object Convert(object value, Type targetType, object parameter, string la
             {
                 return task.GetResultOrDefault();
             }
+            else if (value is null)
+            {
+                return null;
+            }
 
-            return DependencyProperty.UnsetValue;
+            // Otherwise, we'll just pass through whatever value/result was given to us.
+            return value;
         }
 
         /// <inheritdoc/>

UnitTests/UnitTests.UWP/Converters/Test_TaskResultConverter.cs

@@ -17,97 +17,118 @@ public class Test_TaskResultConverter
     {
         [TestCategory("Converters")]
         [UITestMethod]
+        [Ignore] // Ignore this value type test. Behavior will return null currently and not default.
         public void Test_TaskResultConverter_Instance_Int32()
         {
-            var converter = new TaskResultConverter();
+            TaskResultConverter converter = new();
 
-            TaskCompletionSource<int> tcs = new TaskCompletionSource<int>();
+            TaskCompletionSource<int> tcs = new();
 
-            Assert.AreEqual(null, converter.Convert(tcs.Task, null, null, null));
+            Assert.AreEqual(0, (int)converter.Convert(tcs.Task, typeof(int), null, null));
 
             tcs.SetCanceled();
 
-            Assert.AreEqual(null, converter.Convert(tcs.Task, null, null, null));
+            Assert.AreEqual(0, (int)converter.Convert(tcs.Task, typeof(int), null, null));
 
             tcs = new TaskCompletionSource<int>();
 
             tcs.SetException(new InvalidOperationException("Test"));
 
-            Assert.AreEqual(null, converter.Convert(tcs.Task, null, null, null));
+            Assert.AreEqual(0, (int)converter.Convert(tcs.Task, typeof(int), null, null));
 
             tcs = new TaskCompletionSource<int>();
 
             tcs.SetResult(42);
 
-            Assert.AreEqual(42, converter.Convert(tcs.Task, null, null, null));
+            Assert.AreEqual(42, (int)converter.Convert(tcs.Task, typeof(int), null, null));
         }
 
         [TestCategory("Converters")]
         [UITestMethod]
         public void Test_TaskResultConverter_Instance_String()
         {
-            var converter = new TaskResultConverter();
+            TaskResultConverter converter = new();
 
-            TaskCompletionSource<string> tcs = new TaskCompletionSource<string>();
+            TaskCompletionSource<string> tcs = new();
 
-            Assert.AreEqual(null, converter.Convert(tcs.Task, null, null, null));
+            Assert.AreEqual(null, (string)converter.Convert(tcs.Task, typeof(string), null, null));
 
             tcs.SetCanceled();
 
-            Assert.AreEqual(null, converter.Convert(tcs.Task, null, null, null));
+            Assert.AreEqual(null, (string)converter.Convert(tcs.Task, typeof(string), null, null));
 
-            tcs = new TaskCompletionSource<string>();
+            tcs = new();
 
             tcs.SetException(new InvalidOperationException("Test"));
 
-            Assert.AreEqual(null, converter.Convert(tcs.Task, null, null, null));
+            Assert.AreEqual(null, (string)converter.Convert(tcs.Task, typeof(string), null, null));
 
-            tcs = new TaskCompletionSource<string>();
+            tcs = new();
 
             tcs.SetResult("Hello world");
 
-            Assert.AreEqual("Hello world", converter.Convert(tcs.Task, null, null, null));
+            Assert.AreEqual("Hello world", (string)converter.Convert(tcs.Task, typeof(string), null, null));
         }
 
         [TestCategory("Converters")]
         [UITestMethod]
-        public void Test_TaskResultConverter_Instance_UnsetValue()
+        public void Test_TaskResultConverter_Instance_RawValue()
         {
-            var converter = new TaskResultConverter();
+            TaskResultConverter converter = new();
 
-            Assert.AreEqual(DependencyProperty.UnsetValue, converter.Convert(null, null, null, null));
-            Assert.AreEqual(DependencyProperty.UnsetValue, converter.Convert("Hello world", null, null, null));
+            Assert.AreEqual(42, converter.Convert(42, null, null, null));
+
+            Assert.AreEqual(42, converter.Convert(42, typeof(int), null, null));
+
+            Assert.AreEqual("Hello world", converter.Convert("Hello world", null, null, null));
+
+            Assert.AreEqual("Hello world", converter.Convert("Hello world", typeof(string), null, null));
         }
 
         [TestCategory("Converters")]
         [UITestMethod]
-        public void Test_TaskResultConverter_Instance_Null()
+        public void Test_TaskResultConverter_Instance_NullObject()
         {
-            var converter = new TaskResultConverter();
+            TaskResultConverter converter = new();
 
-            var cts = new CancellationTokenSource();
+            Assert.AreEqual(null, converter.Convert(null, null, null, null));
 
-            cts.Cancel();
+            // TODO: Think there may still be a problem for value types in x:Bind expressions, represented by these tests here,
+            // but was going to be too big a change for 7.1.3, will have to get more feedback and evaluate later.
+            /*Assert.AreEqual(0, (int)converter.Convert(null, typeof(int), null, null));
 
-            Assert.AreEqual(null, converter.Convert(Task.FromCanceled(cts.Token), null, null, null));
-            Assert.AreEqual(null, converter.Convert(Task.FromException(new Exception()), null, null, null));
-            Assert.AreEqual(null, converter.Convert(Task.CompletedTask, null, null, null));
+            Assert.AreEqual(false, (bool)converter.Convert(null, typeof(bool), null, null));*/
 
-            TaskCompletionSource<int> tcs1 = new TaskCompletionSource<int>();
+            Assert.AreEqual(null, converter.Convert(null, typeof(int), null, null));
 
-            Assert.AreEqual(null, converter.Convert(tcs1.Task, null, null, null));
+            Assert.AreEqual(null, converter.Convert(null, typeof(bool), null, null));
 
-            TaskCompletionSource<string> tcs2 = new TaskCompletionSource<string>();
+            Assert.AreEqual(null, (int?)converter.Convert(null, typeof(int?), null, null));
 
-            Assert.AreEqual(null, converter.Convert(tcs2.Task, null, null, null));
+            Assert.AreEqual(null, (string)converter.Convert(null, typeof(string), null, null));
+        }
+
+        [TestCategory("Converters")]
+        [UITestMethod]
+        public void Test_TaskResultConverter_Instance_TaskNull()
+        {
+            TaskResultConverter converter = new();
+
+            CancellationTokenSource cts = new();
+
+            cts.Cancel();
+
+            Assert.AreEqual(null, converter.Convert(Task.FromCanceled(cts.Token), null, null, null));
+            Assert.AreEqual(null, converter.Convert(Task.FromException(new Exception()), null, null, null));
+            Assert.AreEqual(null, converter.Convert(Task.CompletedTask, null, null, null));
         }
 
         [TestCategory("Converters")]
         [UITestMethod]
         [ExpectedException(typeof(NotImplementedException))]
         public void Test_TaskResultConverter_Instance_ConvertBack()
         {
-            var converter = new TaskResultConverter();
+            TaskResultConverter converter = new();
 
             Assert.AreEqual(null, converter.ConvertBack(null, null, null, null));
         }