Add an InputHidden component for Blazor

src/Components/Web/src/Forms/InputHidden.cs

@@ -0,0 +1,44 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics.CodeAnalysis;
+using Microsoft.AspNetCore.Components.Rendering;
+
+namespace Microsoft.AspNetCore.Components.Forms;
+
+/// <summary>
+/// An hidden input component for storing <see cref="string"/> values.
+/// </summary>
+public class InputHidden : InputBase<string?>
+{
+    /// <summary>
+    /// Gets or sets the associated <see cref="ElementReference"/>.
+    /// <para>
+    /// May be <see langword="null"/> if accessed before the component is rendered.
+    /// </para>
+    /// </summary>
+    [DisallowNull] public ElementReference? Element { get; protected set; }
+
+    /// <inheritdoc />
+    protected override void BuildRenderTree(RenderTreeBuilder builder)
+    {
+        builder.OpenElement(0, "input");
+        builder.AddAttribute(1, "type", "hidden");
+        builder.AddMultipleAttributes(2, AdditionalAttributes);
+        builder.AddAttributeIfNotNullOrEmpty(3, "name", NameAttributeValue);
+        builder.AddAttributeIfNotNullOrEmpty(4, "class", CssClass);
+        builder.AddAttribute(5, "value", CurrentValueAsString);
+        builder.AddAttribute(6, "onchange", EventCallback.Factory.CreateBinder<string?>(this, __value => CurrentValueAsString = __value, CurrentValueAsString));
+        builder.SetUpdatesAttributeName("value");
+        builder.AddElementReferenceCapture(7, __inputReference => Element = __inputReference);
+        builder.CloseElement();
+    }
+
+    /// <inheritdoc />
+    protected override bool TryParseValueFromString(string? value, out string? result, [NotNullWhen(false)] out string? validationErrorMessage)
+    {
+        result = value;
+        validationErrorMessage = null;
+        return true;
+    }
+}

src/Components/Web/src/PublicAPI.Unshipped.txt

@@ -1,3 +1,9 @@
 #nullable enable
+Microsoft.AspNetCore.Components.Forms.InputHidden
+Microsoft.AspNetCore.Components.Forms.InputHidden.Element.get -> Microsoft.AspNetCore.Components.ElementReference?
+Microsoft.AspNetCore.Components.Forms.InputHidden.Element.set -> void
+Microsoft.AspNetCore.Components.Forms.InputHidden.InputHidden() -> void
 Microsoft.AspNetCore.Components.Web.Internal.IInternalWebJSInProcessRuntime.InvokeJS(in Microsoft.JSInterop.Infrastructure.JSInvocationInfo invocationInfo) -> string!
+override Microsoft.AspNetCore.Components.Forms.InputHidden.BuildRenderTree(Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder! builder) -> void
+override Microsoft.AspNetCore.Components.Forms.InputHidden.TryParseValueFromString(string? value, out string? result, out string? validationErrorMessage) -> bool
 virtual Microsoft.AspNetCore.Components.Routing.NavLink.ShouldMatch(string! uriAbsolute) -> bool

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

@@ -0,0 +1,30 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Microsoft.AspNetCore.Components.Forms;
+
+public class InputHiddenTest
+{
+    [Fact]
+    public async Task InputElementIsAssignedSuccessfully()
+    {
+        // Arrange
+        var model = new TestModel();
+        var rootComponent = new TestInputHostComponent<string, InputHidden>
+        {
+            EditContext = new EditContext(model),
+            ValueExpression = () => model.StringProperty,
+        };
+
+        // Act
+        var inputHiddenComponent = await InputRenderer.RenderAndGetComponent(rootComponent);
+
+        // Assert
+        Assert.NotNull(inputHiddenComponent.Element);
+    }
+
+    private class TestModel
+    {
+        public string StringProperty { get; set; }
+    }
+}

src/Components/test/E2ETest/ServerRenderingTests/FormHandlingTests/FormWithParentBindingContextTest.cs

@@ -104,6 +104,23 @@ public void CanBindParameterToTheDefaultForm(bool suppressEnhancedNavigation)
         DispatchToFormCore(dispatchToForm);
     }
 
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    public void InputHiddenCanStoreData(bool suppressEnhancedNavigation)
+    {
+        var dispatchToForm = new DispatchToForm(this)
+        {
+            Url = "forms/default-form-input-hidden",
+            FormCssSelector = "form",
+            SuppressEnhancedNavigation = suppressEnhancedNavigation,
+        };
+        DispatchToFormCore(dispatchToForm);
+
+        Browser.Equal("stranger", () => Browser.Exists(By.Id("hidden")).GetDomProperty("value"));
+        Browser.Equal("Hello stranger!", () => Browser.Exists(By.Id("pass")).Text);
+    }
+
     [Theory]
     [InlineData(true)]
     [InlineData(false)]

src/Components/test/testassets/Components.TestServer/RazorComponents/Pages/Forms/DefaultFormInputHidden.razor

@@ -0,0 +1,21 @@
+@page "/forms/default-form-input-hidden"
+@page "/reexecution/forms/default-form-input-hidden"
+@using Microsoft.AspNetCore.Components.Forms
+
+<h2>Default form Input Hidden</h2>
+
+<EditForm Enhance Model="Parameter" method="POST" OnValidSubmit="() => _submitted = true" FormName="someform">
+    <InputHidden id="hidden" @bind-Value="Parameter" />
+    <input id="send" type="submit" value="Send" />
+</EditForm>
+
+@if (_submitted)
+{
+    <p id="pass">Hello @Parameter!</p>
+}
+
+@code {
+    bool _submitted = false;
+
+    [SupplyParameterFromForm] public string Parameter { get; set; } = "stranger";
+}