Blazor supports DisplayName for models

src/Components/Web/src/Forms/DisplayName.cs

@@ -0,0 +1,109 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections.Concurrent;
+using System.ComponentModel;
+using System.ComponentModel.DataAnnotations;
+using System.Linq.Expressions;
+using System.Reflection;
+using Microsoft.AspNetCore.Components.HotReload;
+using Microsoft.AspNetCore.Components.Rendering;
+
+namespace Microsoft.AspNetCore.Components.Forms;
+
+/// <summary>
+/// Displays the display name for a specified field, reading from <see cref="DisplayAttribute"/>
+/// or <see cref="DisplayNameAttribute"/> if present, or falling back to the property name.
+/// </summary>
+/// <typeparam name="TValue">The type of the field.</typeparam>
+public class DisplayName<TValue> : IComponent
+{
+    private static readonly ConcurrentDictionary<MemberInfo, string> _displayNameCache = new();
+
+    private RenderHandle _renderHandle;
+    private Expression<Func<TValue>>? _previousFieldAccessor;
+    private string? _displayName;
+
+    /// <summary>
+    /// Specifies the field for which the display name should be shown.
+    /// </summary>
+    [Parameter, EditorRequired]
+    public Expression<Func<TValue>>? For { get; set; }
+
+    static DisplayName()
+    {
+        if (HotReloadManager.Default.MetadataUpdateSupported)
+        {
+            HotReloadManager.Default.OnDeltaApplied += ClearCache;
+        }
+    }
+
+    /// <inheritdoc />
+    void IComponent.Attach(RenderHandle renderHandle)
+    {
+        _renderHandle = renderHandle;
+    }
+
+    /// <inheritdoc />
+    Task IComponent.SetParametersAsync(ParameterView parameters)
+    {
+        parameters.SetParameterProperties(this);
+
+        if (For is null)
+        {
+            throw new InvalidOperationException($"{GetType()} requires a value for the " +
+                $"{nameof(For)} parameter.");
+        }
+
+        // Only recalculate if the expression changed
+        if (For != _previousFieldAccessor)
+        {
+            var member = ExpressionMemberAccessor.GetMemberInfo(For);
+            var newDisplayName = GetDisplayName(member);
+
+            if (newDisplayName != _displayName)
+            {
+                _displayName = newDisplayName;
+                _renderHandle.Render(BuildRenderTree);
+            }
+
+            _previousFieldAccessor = For;
+        }
+
+        return Task.CompletedTask;
+    }
+
+    private void BuildRenderTree(RenderTreeBuilder builder)
+    {
+        builder.AddContent(0, _displayName);
+    }
+
+    private static string GetDisplayName(MemberInfo member)
+    {
+        return _displayNameCache.GetOrAdd(member, static m =>
+        {
+            var displayAttribute = m.GetCustomAttribute<DisplayAttribute>();
+            if (displayAttribute is not null)
+            {
+                var name = displayAttribute.GetName();
+                if (name is not null)
+                {
+                    return name;
+                }
+            }
+
+            var displayNameAttribute = m.GetCustomAttribute<DisplayNameAttribute>();
+            if (displayNameAttribute?.DisplayName is not null)
+            {
+                return displayNameAttribute.DisplayName;
+            }
+
+            return m.Name;
+        });
+    }
+
+    private static void ClearCache()
+    {
+        _displayNameCache.Clear();
+    }
+}

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

@@ -0,0 +1,54 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections.Concurrent;
+using System.Linq.Expressions;
+using System.Reflection;
+using Microsoft.AspNetCore.Components.HotReload;
+
+namespace Microsoft.AspNetCore.Components.Forms;
+
+internal static class ExpressionMemberAccessor
+{
+    private static readonly ConcurrentDictionary<Expression, MemberInfo> _memberInfoCache = new();
+
+    static ExpressionMemberAccessor()
+    {
+        if (HotReloadManager.Default.MetadataUpdateSupported)
+        {
+            HotReloadManager.Default.OnDeltaApplied += ClearCache;
+        }
+    }
+
+    public static MemberInfo GetMemberInfo<TValue>(Expression<Func<TValue>> accessor)
+    {
+        ArgumentNullException.ThrowIfNull(accessor);
+
+        return _memberInfoCache.GetOrAdd(accessor, static expr =>
+        {
+            var lambdaExpression = (LambdaExpression)expr;
+            var accessorBody = lambdaExpression.Body;
+
+            if (accessorBody is UnaryExpression unaryExpression
+                && unaryExpression.NodeType == ExpressionType.Convert
+                && unaryExpression.Type == typeof(object))
+            {
+                accessorBody = unaryExpression.Operand;
+            }
+
+            if (accessorBody is not MemberExpression memberExpression)
+            {
+                throw new ArgumentException(
+                    $"The provided expression contains a {accessorBody.GetType().Name} which is not supported. " +
+                    $"Only simple member accessors (fields, properties) of an object are supported.");
+            }
+
+            return memberExpression.Member;
+        });
+    }
+
+    private static void ClearCache()
+    {
+        _memberInfoCache.Clear();
+    }
+}

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

@@ -40,3 +40,7 @@ Microsoft.AspNetCore.Components.Web.Media.MediaSource.MediaSource(byte[]! data,
 Microsoft.AspNetCore.Components.Web.Media.MediaSource.MediaSource(System.IO.Stream! stream, string! mimeType, string! cacheKey) -> void
 Microsoft.AspNetCore.Components.Web.Media.MediaSource.MimeType.get -> string!
 Microsoft.AspNetCore.Components.Web.Media.MediaSource.Stream.get -> System.IO.Stream!
+Microsoft.AspNetCore.Components.Forms.DisplayName<TValue>
+Microsoft.AspNetCore.Components.Forms.DisplayName<TValue>.DisplayName() -> void
+Microsoft.AspNetCore.Components.Forms.DisplayName<TValue>.For.get -> System.Linq.Expressions.Expression<System.Func<TValue>!>?
+Microsoft.AspNetCore.Components.Forms.DisplayName<TValue>.For.set -> void