Make InputBase respond to validation state notifications

src/Components/Web/ref/Microsoft.AspNetCore.Components.Web.netcoreapp.cs

@@ -42,7 +42,7 @@ public EditForm() { }
         protected override void BuildRenderTree(Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder builder) { }
         protected override void OnParametersSet() { }
     }
-    public abstract partial class InputBase<TValue> : Microsoft.AspNetCore.Components.ComponentBase
+    public abstract partial class InputBase<TValue> : Microsoft.AspNetCore.Components.ComponentBase, System.IDisposable
     {
         protected InputBase() { }
         [Microsoft.AspNetCore.Components.ParameterAttribute(CaptureUnmatchedValues=true)]
@@ -58,8 +58,10 @@ protected InputBase() { }
         public Microsoft.AspNetCore.Components.EventCallback<TValue> ValueChanged { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
         [Microsoft.AspNetCore.Components.ParameterAttribute]
         public System.Linq.Expressions.Expression<System.Func<TValue>> ValueExpression { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
+        protected virtual void Dispose(bool disposing) { }
         protected virtual string FormatValueAsString(TValue value) { throw null; }
         public override System.Threading.Tasks.Task SetParametersAsync(Microsoft.AspNetCore.Components.ParameterView parameters) { throw null; }
+        void System.IDisposable.Dispose() { }
         protected abstract bool TryParseValueFromString(string value, out TValue result, out string validationErrorMessage);
     }
     public partial class InputCheckbox : Microsoft.AspNetCore.Components.Forms.InputBase<bool>

src/Components/Web/ref/Microsoft.AspNetCore.Components.Web.netstandard2.0.cs

@@ -42,7 +42,7 @@ public EditForm() { }
         protected override void BuildRenderTree(Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder builder) { }
         protected override void OnParametersSet() { }
     }
-    public abstract partial class InputBase<TValue> : Microsoft.AspNetCore.Components.ComponentBase
+    public abstract partial class InputBase<TValue> : Microsoft.AspNetCore.Components.ComponentBase, System.IDisposable
     {
         protected InputBase() { }
         [Microsoft.AspNetCore.Components.ParameterAttribute(CaptureUnmatchedValues=true)]
@@ -58,8 +58,10 @@ protected InputBase() { }
         public Microsoft.AspNetCore.Components.EventCallback<TValue> ValueChanged { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
         [Microsoft.AspNetCore.Components.ParameterAttribute]
         public System.Linq.Expressions.Expression<System.Func<TValue>> ValueExpression { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
+        protected virtual void Dispose(bool disposing) { }
         protected virtual string FormatValueAsString(TValue value) { throw null; }
         public override System.Threading.Tasks.Task SetParametersAsync(Microsoft.AspNetCore.Components.ParameterView parameters) { throw null; }
+        void System.IDisposable.Dispose() { }
         protected abstract bool TryParseValueFromString(string value, out TValue result, out string validationErrorMessage);
     }
     public partial class InputCheckbox : Microsoft.AspNetCore.Components.Forms.InputBase<bool>

src/Components/Web/src/Forms/InputBase.cs

@@ -13,8 +13,9 @@ namespace Microsoft.AspNetCore.Components.Forms
     /// integrates with an <see cref="Forms.EditContext"/>, which must be supplied
     /// as a cascading parameter.
     /// </summary>
-    public abstract class InputBase<TValue> : ComponentBase
+    public abstract class InputBase<TValue> : ComponentBase, IDisposable
     {
+        private readonly EventHandler<ValidationStateChangedEventArgs> _validationStateChangedHandler;
         private bool _previousParsingAttemptFailed;
         private ValidationMessageStore _parsingValidationMessages;
         private Type _nullableUnderlyingType;
@@ -121,6 +122,14 @@ protected string CurrentValueAsString
             }
         }
 
+        /// <summary>
+        /// Constructs an instance of <see cref="InputBase{TValue}"/>.
+        /// </summary>
+        protected InputBase()
+        {
+            _validationStateChangedHandler = (sender, eventArgs) => StateHasChanged();
+        }
+
         /// <summary>
         /// Formats the value as a string. Derived classes can override this to determine the formating used for <see cref="CurrentValueAsString"/>.
         /// </summary>
@@ -193,6 +202,8 @@ public override Task SetParametersAsync(ParameterView parameters)
                 EditContext = CascadedEditContext;
                 FieldIdentifier = FieldIdentifier.Create(ValueExpression);
                 _nullableUnderlyingType = Nullable.GetUnderlyingType(typeof(TValue));
+
+                EditContext.OnValidationStateChanged += _validationStateChangedHandler;
             }
             else if (CascadedEditContext != EditContext)
             {
@@ -208,5 +219,19 @@ public override Task SetParametersAsync(ParameterView parameters)
             // For derived components, retain the usual lifecycle with OnInit/OnParametersSet/etc.
             return base.SetParametersAsync(ParameterView.Empty);
         }
+
+        protected virtual void Dispose(bool disposing)
+        {
+        }
+
+        void IDisposable.Dispose()
+        {
+            if (EditContext != null)
+            {
+                EditContext.OnValidationStateChanged -= _validationStateChangedHandler;
+            }
+
+            Dispose(disposing: true);
+        }
     }
 }

src/Components/Web/test/Forms/InputBaseTest.cs

@@ -294,7 +294,7 @@ public async Task ParsesCurrentValueAsStringWhenChanged_Valid()
             rootComponent.EditContext.OnValidationStateChanged += (sender, eventArgs) => { numValidationStateChanges++; };
 
             // Act
-            inputComponent.CurrentValueAsString = "1991/11/20";
+            await inputComponent.SetCurrentValueAsStringAsync("1991/11/20");
 
             // Assert
             var receivedParsedValue = valueChangedArgs.Single();
@@ -324,14 +324,14 @@ public async Task ParsesCurrentValueAsStringWhenChanged_Invalid()
             rootComponent.EditContext.OnValidationStateChanged += (sender, eventArgs) => { numValidationStateChanges++; };
 
             // Act/Assert 1: Transition to invalid
-            inputComponent.CurrentValueAsString = "1991/11/40";
+            await inputComponent.SetCurrentValueAsStringAsync("1991/11/40");
             Assert.Empty(valueChangedArgs);
             Assert.True(rootComponent.EditContext.IsModified(fieldIdentifier));
             Assert.Equal(new[] { "Bad date value" }, rootComponent.EditContext.GetValidationMessages(fieldIdentifier));
             Assert.Equal(1, numValidationStateChanges);
 
             // Act/Assert 2: Transition to valid
-            inputComponent.CurrentValueAsString = "1991/11/20";
+            await inputComponent.SetCurrentValueAsStringAsync("1991/11/20");
             var receivedParsedValue = valueChangedArgs.Single();
             Assert.Equal(1991, receivedParsedValue.Year);
             Assert.Equal(11, receivedParsedValue.Month);
@@ -341,6 +341,65 @@ public async Task ParsesCurrentValueAsStringWhenChanged_Invalid()
             Assert.Equal(2, numValidationStateChanges);
         }
 
+        [Fact]
+        public async Task RespondsToValidationStateChangeNotifications()
+        {
+            // Arrange
+            var model = new TestModel();
+            var rootComponent = new TestInputHostComponent<string, TestInputComponent<string>>
+            {
+                EditContext = new EditContext(model),
+                ValueExpression = () => model.StringProperty
+            };
+            var fieldIdentifier = FieldIdentifier.Create(() => model.StringProperty);
+            var renderer = new TestRenderer();
+            var rootComponentId = renderer.AssignRootComponentId(rootComponent);
+            await renderer.RenderRootComponentAsync(rootComponentId);
+
+            // Initally, it rendered one batch and is valid
+            var batch1 = renderer.Batches.Single();
+            var componentFrame1 = batch1.GetComponentFrames<TestInputComponent<string>>().Single();
+            var inputComponentId = componentFrame1.ComponentId;
+            var component = (TestInputComponent<string>)componentFrame1.Component;
+            Assert.Equal("valid", component.CssClass);
+
+            // Act: update the field state in the EditContext and notify
+            var messageStore = new ValidationMessageStore(rootComponent.EditContext);
+            messageStore.Add(fieldIdentifier, "Some message");
+            await renderer.Dispatcher.InvokeAsync(rootComponent.EditContext.NotifyValidationStateChanged);
+
+            // Assert: The input component rendered itself again and now has the new class
+            var batch2 = renderer.Batches.Skip(1).Single();
+            Assert.Equal(inputComponentId, batch2.DiffsByComponentId.Keys.Single());
+            Assert.Equal("invalid", component.CssClass);
+        }
+
+        [Fact]
+        public async Task UnsubscribesFromValidationStateChangeNotifications()
+        {
+            // Arrange
+            var model = new TestModel();
+            var rootComponent = new TestInputHostComponent<string, TestInputComponent<string>>
+            {
+                EditContext = new EditContext(model),
+                ValueExpression = () => model.StringProperty
+            };
+            var fieldIdentifier = FieldIdentifier.Create(() => model.StringProperty);
+            var renderer = new TestRenderer();
+            var rootComponentId = renderer.AssignRootComponentId(rootComponent);
+            await renderer.RenderRootComponentAsync(rootComponentId);
+            var component = renderer.Batches.Single().GetComponentFrames<TestInputComponent<string>>().Single().Component;
+
+            // Act: dispose, then update the field state in the EditContext and notify
+            ((IDisposable)component).Dispose();
+            var messageStore = new ValidationMessageStore(rootComponent.EditContext);
+            messageStore.Add(fieldIdentifier, "Some message");
+            await renderer.Dispatcher.InvokeAsync(rootComponent.EditContext.NotifyValidationStateChanged);
+
+            // Assert: No additional render
+            Assert.Empty(renderer.Batches.Skip(1));
+        }
+
         private static TComponent FindComponent<TComponent>(CapturedBatch batch)
             => batch.ReferenceFrames
                     .Where(f => f.FrameType == RenderTreeFrameType.Component)
@@ -376,7 +435,6 @@ class TestInputComponent<T> : InputBase<T>
             public new string CurrentValueAsString
             {
                 get => base.CurrentValueAsString;
-                set { base.CurrentValueAsString = value; }
             }
 
             public new IReadOnlyDictionary<string, object> AdditionalAttributes => base.AdditionalAttributes;
@@ -391,6 +449,15 @@ protected override bool TryParseValueFromString(string value, out T result, out
             {
                 throw new NotImplementedException();
             }
+
+            public async Task SetCurrentValueAsStringAsync(string value)
+            {
+                // This is equivalent to the subclass writing to CurrentValueAsString
+                // (e.g., from @bind), except to simplify the test code there's an InvokeAsync
+                // here. In production code it wouldn't normally be required because @bind
+                // calls run on the sync context anyway.
+                await InvokeAsync(() => { base.CurrentValueAsString = value; });
+            }
         }
 
         class TestDateInputComponent : TestInputComponent<DateTime>

src/Components/test/E2ETest/Tests/FormsTest.cs

@@ -376,6 +376,24 @@ public void InputComponentsCauseContainerToRerenderOnChange()
             Browser.Equal("Premium", () => selectedTicketClassDisplay.Text);
         }
 
+        [Fact]
+        public void InputComponentsRespondToAsynchronouslyAddedMessages()
+        {
+            var appElement = Browser.MountTestComponent<TypicalValidationComponent>();
+            var input = appElement.FindElement(By.CssSelector(".username input"));
+            var triggerAsyncErrorButton = appElement.FindElement(By.CssSelector(".username button"));
+            var messagesAccessor = CreateValidationMessagesAccessor(appElement);
+
+            // Initially shows no error
+            Browser.Empty(() => messagesAccessor());
+            Browser.Equal("valid", () => input.GetAttribute("class"));
+
+            // Can trigger async error
+            triggerAsyncErrorButton.Click();
+            Browser.Equal(new[] { "This is invalid, asynchronously" }, messagesAccessor);
+            Browser.Equal("invalid", () => input.GetAttribute("class"));
+        }
+
         private Func<string[]> CreateValidationMessagesAccessor(IWebElement appElement)
         {
             return () => appElement.FindElements(By.ClassName("validation-message"))

src/Components/test/testassets/BasicTestApp/FormsTest/TypicalValidationComponent.razor

@@ -1,7 +1,7 @@
 @using System.ComponentModel.DataAnnotations
 @using Microsoft.AspNetCore.Components.Forms
 
-<EditForm Model="@person" OnValidSubmit="@HandleValidSubmit">
+<EditForm EditContext="@editContext" OnValidSubmit="@HandleValidSubmit">
     <DataAnnotationsValidator />
 
     <p class="name">
@@ -42,6 +42,10 @@
     <p class="is-evil">
         Is evil: <InputCheckbox @bind-Value="person.IsEvil" />
     </p>
+    <p class="username">
+        Username (optional): <InputText @bind-Value="person.Username" />
+        <button type="button" @onclick="@TriggerAsyncValidationError">Trigger async error</button>
+    </p>
 
     <button type="submit">Submit</button>
 
@@ -52,6 +56,14 @@
 
 @code {
     Person person = new Person();
+    EditContext editContext;
+    ValidationMessageStore customValidationMessageStore;
+
+    protected override void OnInitialized()
+    {
+        editContext = new EditContext(person);
+        customValidationMessageStore = new ValidationMessageStore(editContext);
+    }
 
     // Usually this would be in a different file
     class Person
@@ -83,6 +95,8 @@
 
         [Required, EnumDataType(typeof(TicketClass))]
         public TicketClass TicketClass { get; set; }
+
+        public string Username { get; set; }
     }
 
     enum TicketClass { Economy, Premium, First }
@@ -93,4 +107,22 @@
     {
         submissionLog.Add("OnValidSubmit");
     }
+
+    void TriggerAsyncValidationError()
+    {
+        customValidationMessageStore.Clear();
+
+        // Note that this method returns void, so the renderer doesn't react to
+        // its async flow by default. This is to simulate some external system
+        // implementing async validation.
+        Task.Run(async () =>
+        {
+            // The duration of the delay doesn't matter to the test, as long as it's not
+            // so long that we time out. Picking a value that's long enough for humans
+            // to observe the asynchrony too.
+            await Task.Delay(500);
+            customValidationMessageStore.Add(editContext.Field(nameof(Person.Username)), "This is invalid, asynchronously");
+            _ = InvokeAsync(editContext.NotifyValidationStateChanged);
+        });
+    }
 }