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ilonatommyCopilotjaviercn
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Blazor supports DisplayName for models (#64636)
* API proposal. * Unit tests. * Add E2E tests. * Update templates to use the new feature. Co-authored-by: Copilot <[email protected]> * Feedback: use same caching approach as `FieldIdentifier` uses. * Feedback: use the infrastructure from `ValidationMessage`. * Feedback: Make sure localization is supported. * Feedback: helper class can handle cache. Co-authored-by: Javier Calvarro Nelson <[email protected]> --------- Co-authored-by: Copilot <[email protected]> Co-authored-by: Javier Calvarro Nelson <[email protected]>
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‎src/Components/Web/src/Forms/DisplayName.cs‎

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// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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using System.ComponentModel;
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using System.ComponentModel.DataAnnotations;
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using System.Linq.Expressions;
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using Microsoft.AspNetCore.Components.Rendering;
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namespace Microsoft.AspNetCore.Components.Forms;
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/// <summary>
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/// Displays the display name for a specified field, reading from <see cref="DisplayAttribute"/>
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/// or <see cref="DisplayNameAttribute"/> if present, or falling back to the property name.
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/// </summary>
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/// <typeparam name="TValue">The type of the field.</typeparam>
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public class DisplayName<TValue> : IComponent
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{
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private RenderHandle _renderHandle;
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private Expression<Func<TValue>>? _previousFieldAccessor;
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private string? _displayName;
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/// <summary>
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/// Specifies the field for which the display name should be shown.
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/// </summary>
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[Parameter, EditorRequired]
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public Expression<Func<TValue>>? For { get; set; }
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/// <inheritdoc />
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void IComponent.Attach(RenderHandle renderHandle)
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{
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_renderHandle = renderHandle;
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}
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/// <inheritdoc />
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Task IComponent.SetParametersAsync(ParameterView parameters)
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{
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parameters.SetParameterProperties(this);
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if (For is null)
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{
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throw new InvalidOperationException($"{GetType()} requires a value for the " +
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$"{nameof(For)} parameter.");
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}
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// Only recalculate if the expression changed
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if (For != _previousFieldAccessor)
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{
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var newDisplayName = ExpressionMemberAccessor.GetDisplayName(For);
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if (newDisplayName != _displayName)
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{
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_displayName = newDisplayName;
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_renderHandle.Render(BuildRenderTree);
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}
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_previousFieldAccessor = For;
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}
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return Task.CompletedTask;
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}
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private void BuildRenderTree(RenderTreeBuilder builder)
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{
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builder.AddContent(0, _displayName);
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}
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}

‎src/Components/Web/src/Forms/ExpressionMemberAccessor.cs‎

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// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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using System.Collections.Concurrent;
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using System.ComponentModel;
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using System.ComponentModel.DataAnnotations;
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using System.Linq.Expressions;
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using System.Reflection;
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using Microsoft.AspNetCore.Components.HotReload;
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namespace Microsoft.AspNetCore.Components.Forms;
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internal static class ExpressionMemberAccessor
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{
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private static readonly ConcurrentDictionary<Expression, MemberInfo> _memberInfoCache = new();
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private static readonly ConcurrentDictionary<MemberInfo, string> _displayNameCache = new();
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static ExpressionMemberAccessor()
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{
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if (HotReloadManager.Default.MetadataUpdateSupported)
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{
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HotReloadManager.Default.OnDeltaApplied += ClearCache;
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}
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}
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private static MemberInfo GetMemberInfo<TValue>(Expression<Func<TValue>> accessor)
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{
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ArgumentNullException.ThrowIfNull(accessor);
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return _memberInfoCache.GetOrAdd(accessor, static expr =>
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{
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var lambdaExpression = (LambdaExpression)expr;
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var accessorBody = lambdaExpression.Body;
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if (accessorBody is UnaryExpression unaryExpression
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&& unaryExpression.NodeType == ExpressionType.Convert
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&& unaryExpression.Type == typeof(object))
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{
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accessorBody = unaryExpression.Operand;
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}
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if (accessorBody is not MemberExpression memberExpression)
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{
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throw new ArgumentException(
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$"The provided expression contains a {accessorBody.GetType().Name} which is not supported. " +
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$"Only simple member accessors (fields, properties) of an object are supported.");
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}
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return memberExpression.Member;
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});
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}
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public static string GetDisplayName(MemberInfo member)
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{
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ArgumentNullException.ThrowIfNull(member);
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return _displayNameCache.GetOrAdd(member, static m =>
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{
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var displayAttribute = m.GetCustomAttribute<DisplayAttribute>();
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if (displayAttribute is not null)
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{
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var name = displayAttribute.GetName();
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if (name is not null)
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{
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return name;
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}
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}
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var displayNameAttribute = m.GetCustomAttribute<DisplayNameAttribute>();
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if (displayNameAttribute?.DisplayName is not null)
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{
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return displayNameAttribute.DisplayName;
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}
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return m.Name;
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});
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}
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public static string GetDisplayName<TValue>(Expression<Func<TValue>> accessor)
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{
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ArgumentNullException.ThrowIfNull(accessor);
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var member = GetMemberInfo(accessor);
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return GetDisplayName(member);
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}
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private static void ClearCache()
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{
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_memberInfoCache.Clear();
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_displayNameCache.Clear();
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}
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}

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

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Microsoft.AspNetCore.Components.Web.Media.MediaSource.MediaSource(System.IO.Stream! stream, string! mimeType, string! cacheKey) -> void
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Microsoft.AspNetCore.Components.Web.Media.MediaSource.MimeType.get -> string!
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Microsoft.AspNetCore.Components.Web.Media.MediaSource.Stream.get -> System.IO.Stream!
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Microsoft.AspNetCore.Components.Forms.DisplayName<TValue>
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Microsoft.AspNetCore.Components.Forms.DisplayName<TValue>.DisplayName() -> void
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Microsoft.AspNetCore.Components.Forms.DisplayName<TValue>.For.get -> System.Linq.Expressions.Expression<System.Func<TValue>!>?
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Microsoft.AspNetCore.Components.Forms.DisplayName<TValue>.For.set -> void

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

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// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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using System.ComponentModel;
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using System.ComponentModel.DataAnnotations;
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using Microsoft.AspNetCore.Components.Rendering;
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using Microsoft.AspNetCore.Components.Test.Helpers;
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namespace Microsoft.AspNetCore.Components.Forms;
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public class DisplayNameTest
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{
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[Fact]
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public async Task ThrowsIfNoForParameterProvided()
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{
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// Arrange
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var rootComponent = new TestHostComponent
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{
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InnerContent = builder =>
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{
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builder.OpenComponent<DisplayName<string>>(0);
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builder.CloseComponent();
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}
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};
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var testRenderer = new TestRenderer();
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var componentId = testRenderer.AssignRootComponentId(rootComponent);
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// Act & Assert
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var ex = await Assert.ThrowsAsync<InvalidOperationException>(
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async () => await testRenderer.RenderRootComponentAsync(componentId));
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Assert.Contains("For", ex.Message);
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Assert.Contains("parameter", ex.Message);
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}
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[Fact]
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public async Task DisplaysPropertyNameWhenNoAttributePresent()
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{
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// Arrange
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var model = new TestModel();
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var rootComponent = new TestHostComponent
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{
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InnerContent = builder =>
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{
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builder.OpenComponent<DisplayName<string>>(0);
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builder.AddComponentParameter(1, "For", (System.Linq.Expressions.Expression<Func<string>>)(() => model.PlainProperty));
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builder.CloseComponent();
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}
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};
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// Act
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var output = await RenderAndGetOutput(rootComponent);
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// Assert
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Assert.Equal("PlainProperty", output);
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}
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[Fact]
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public async Task DisplaysDisplayAttributeName()
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{
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// Arrange
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var model = new TestModel();
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var rootComponent = new TestHostComponent
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{
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InnerContent = builder =>
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{
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builder.OpenComponent<DisplayName<string>>(0);
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builder.AddComponentParameter(1, "For", (System.Linq.Expressions.Expression<Func<string>>)(() => model.PropertyWithDisplayAttribute));
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builder.CloseComponent();
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}
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};
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// Act
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var output = await RenderAndGetOutput(rootComponent);
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// Assert
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Assert.Equal("Custom Display Name", output);
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}
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[Fact]
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public async Task DisplaysDisplayNameAttributeName()
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{
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// Arrange
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var model = new TestModel();
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var rootComponent = new TestHostComponent
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{
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InnerContent = builder =>
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{
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builder.OpenComponent<DisplayName<string>>(0);
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builder.AddComponentParameter(1, "For", (System.Linq.Expressions.Expression<Func<string>>)(() => model.PropertyWithDisplayNameAttribute));
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builder.CloseComponent();
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}
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};
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// Act
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var output = await RenderAndGetOutput(rootComponent);
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// Assert
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Assert.Equal("Custom DisplayName", output);
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}
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[Fact]
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public async Task DisplayAttributeTakesPrecedenceOverDisplayNameAttribute()
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{
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// Arrange
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var model = new TestModel();
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var rootComponent = new TestHostComponent
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{
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InnerContent = builder =>
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{
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builder.OpenComponent<DisplayName<string>>(0);
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builder.AddComponentParameter(1, "For", (System.Linq.Expressions.Expression<Func<string>>)(() => model.PropertyWithBothAttributes));
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builder.CloseComponent();
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}
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};
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// Act
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var output = await RenderAndGetOutput(rootComponent);
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// Assert
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// DisplayAttribute should take precedence per MVC conventions
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Assert.Equal("Display Takes Precedence", output);
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}
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[Fact]
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public async Task WorksWithDifferentPropertyTypes()
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{
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// Arrange
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var model = new TestModel();
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var intComponent = new TestHostComponent
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{
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InnerContent = builder =>
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{
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builder.OpenComponent<DisplayName<int>>(0);
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builder.AddComponentParameter(1, "For", (System.Linq.Expressions.Expression<Func<int>>)(() => model.IntProperty));
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builder.CloseComponent();
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}
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};
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var dateComponent = new TestHostComponent
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{
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InnerContent = builder =>
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{
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builder.OpenComponent<DisplayName<DateTime>>(0);
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builder.AddComponentParameter(1, "For", (System.Linq.Expressions.Expression<Func<DateTime>>)(() => model.DateProperty));
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builder.CloseComponent();
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}
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};
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// Act
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var intOutput = await RenderAndGetOutput(intComponent);
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var dateOutput = await RenderAndGetOutput(dateComponent);
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// Assert
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Assert.Equal("Integer Value", intOutput);
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Assert.Equal("Date Value", dateOutput);
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}
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[Fact]
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public async Task SupportsLocalizationWithResourceType()
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{
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var model = new TestModel();
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var rootComponent = new TestHostComponent
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{
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InnerContent = builder =>
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{
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builder.OpenComponent<DisplayName<string>>(0);
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builder.AddComponentParameter(1, "For", (System.Linq.Expressions.Expression<Func<string>>)(() => model.PropertyWithResourceBasedDisplay));
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builder.CloseComponent();
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}
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};
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var output = await RenderAndGetOutput(rootComponent);
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Assert.Equal("Localized Display Name", output);
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}
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private static async Task<string> RenderAndGetOutput(TestHostComponent rootComponent)
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{
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var testRenderer = new TestRenderer();
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var componentId = testRenderer.AssignRootComponentId(rootComponent);
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await testRenderer.RenderRootComponentAsync(componentId);
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var batch = testRenderer.Batches.Single();
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var displayLabelComponentFrame = batch.ReferenceFrames
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.First(f => f.FrameType == RenderTree.RenderTreeFrameType.Component &&
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f.Component is DisplayName<string> or DisplayName<int> or DisplayName<DateTime>);
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// Find the text content frame within the component
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var textFrame = batch.ReferenceFrames
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.First(f => f.FrameType == RenderTree.RenderTreeFrameType.Text);
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return textFrame.TextContent;
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}
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private class TestHostComponent : ComponentBase
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{
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public RenderFragment InnerContent { get; set; }
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protected override void BuildRenderTree(RenderTreeBuilder builder)
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{
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InnerContent(builder);
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}
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}
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private class TestModel
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{
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public string PlainProperty { get; set; } = string.Empty;
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[Display(Name = "Custom Display Name")]
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public string PropertyWithDisplayAttribute { get; set; } = string.Empty;
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[DisplayName("Custom DisplayName")]
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public string PropertyWithDisplayNameAttribute { get; set; } = string.Empty;
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[Display(Name = "Display Takes Precedence")]
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[DisplayName("This Should Not Be Used")]
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public string PropertyWithBothAttributes { get; set; } = string.Empty;
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[Display(Name = "Integer Value")]
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public int IntProperty { get; set; }
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[Display(Name = "Date Value")]
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public DateTime DateProperty { get; set; }
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[Display(Name = nameof(TestResources.LocalizedDisplayName), ResourceType = typeof(TestResources))]
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public string PropertyWithResourceBasedDisplay { get; set; } = string.Empty;
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}
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public static class TestResources
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{
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public static string LocalizedDisplayName => "Localized Display Name";
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}
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}

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