[Blazor] Take cascading parameter attribute type into account when supplying cascading values

src/Components/Authorization/test/AuthorizeRouteViewTest.cs

@@ -34,7 +34,6 @@ public AuthorizeRouteViewTest()
         serviceCollection.AddSingleton<IAuthorizationPolicyProvider, TestAuthorizationPolicyProvider>();
         serviceCollection.AddSingleton<IAuthorizationService>(_testAuthorizationService);
         serviceCollection.AddSingleton<NavigationManager, TestNavigationManager>();
-        serviceCollection.AddSingleton<IFormValueSupplier, TestFormValueSupplier>();
 
         var services = serviceCollection.BuildServiceProvider();
         _renderer = new TestRenderer(services);

src/Components/Components/src/Binding/CascadingModelBinder.cs

@@ -1,6 +1,8 @@
 // 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 System.Linq;
 using System.Reflection.Metadata;
 using Microsoft.AspNetCore.Components.Binding;
 using Microsoft.AspNetCore.Components.Rendering;
@@ -11,12 +13,13 @@ namespace Microsoft.AspNetCore.Components;
 /// <summary>
 /// Defines the binding context for data bound from external sources.
 /// </summary>
-public sealed class CascadingModelBinder : IComponent, ICascadingValueComponent, IDisposable
+public sealed class CascadingModelBinder : IComponent, ICascadingValueSupplier, IDisposable
 {
+    private readonly Dictionary<Type, CascadingModelBindingProvider?> _providersByCascadingParameterAttributeType = new();
+
     private RenderHandle _handle;
     private ModelBindingContext? _bindingContext;
     private bool _hasPendingQueuedRender;
-    private BindingInfo? _bindingInfo;
 
     /// <summary>
     /// The binding context name.
@@ -40,7 +43,9 @@ public sealed class CascadingModelBinder : IComponent, ICascadingValueComponent,
 
     [Inject] internal NavigationManager Navigation { get; set; } = null!;
 
-    [Inject] internal IFormValueSupplier FormValueSupplier { get; set; } = null!;
+    [Inject] internal IEnumerable<CascadingModelBindingProvider> ModelBindingProviders { get; set; } = Enumerable.Empty<CascadingModelBindingProvider>();
+
+    internal ModelBindingContext? BindingContext => _bindingContext;
 
     void IComponent.Attach(RenderHandle renderHandle)
     {
@@ -110,85 +115,118 @@ internal void UpdateBindingInformation(string url)
         // BindingContextId = <<base-relative-uri>>((<<existing-query>>&)|?)handler=my-handler
         var name = ModelBindingContext.Combine(ParentContext, Name);
         var bindingId = string.IsNullOrEmpty(name) ? "" : GenerateBindingContextId(name);
+        var bindingContextDidChange =
+            _bindingContext is null ||
+            !string.Equals(_bindingContext.Name, name, StringComparison.Ordinal) ||
+            !string.Equals(_bindingContext.BindingContextId, bindingId, StringComparison.Ordinal);
 
-        var bindingContext = _bindingContext != null &&
-            string.Equals(_bindingContext.Name, name, StringComparison.Ordinal) &&
-            string.Equals(_bindingContext.BindingContextId, bindingId, StringComparison.Ordinal) ?
-            _bindingContext : new ModelBindingContext(name, bindingId, FormValueSupplier.CanConvertSingleValue);
-
-        // It doesn't matter that we don't check IsFixed, since the CascadingValue we are setting up will throw if the app changes.
-        if (IsFixed && _bindingContext != null && _bindingContext != bindingContext)
+        if (bindingContextDidChange)
         {
-            // Throw an exception if either the Name or the BindingContextId changed. Once a CascadingModelBinder has been initialized
-            // as fixed, it can't change it's name nor its BindingContextId. This can happen in several situations:
-            // * Component ParentContext hierarchy changes.
-            //   * Technically, the component won't be retained in this case and will be destroyed instead.
-            // * A parent changes Name.
-            throw new InvalidOperationException($"'{nameof(CascadingModelBinder)}' 'Name' can't change after initialized.");
-        }
+            if (IsFixed && _bindingContext is not null)
+            {
+                // Throw an exception if either the Name or the BindingContextId changed. Once a CascadingModelBinder has been initialized
+                // as fixed, it can't change it's name nor its BindingContextId. This can happen in several situations:
+                // * Component ParentContext hierarchy changes.
+                //   * Technically, the component won't be retained in this case and will be destroyed instead.
+                // * A parent changes Name.
+                throw new InvalidOperationException($"'{nameof(CascadingModelBinder)}' 'Name' can't change after initialized.");
+            }
 
-        _bindingContext = bindingContext;
+            _bindingContext = new ModelBindingContext(name, bindingId, CanBind);
+        }
 
         string GenerateBindingContextId(string name)
         {
             var bindingId = Navigation.ToBaseRelativePath(Navigation.GetUriWithQueryParameter("handler", name));
             var hashIndex = bindingId.IndexOf('#');
             return hashIndex == -1 ? bindingId : new string(bindingId.AsSpan(0, hashIndex));
         }
+
+        bool CanBind(Type type)
+        {
+            foreach (var provider in ModelBindingProviders)
+            {
+                if (provider.SupportsParameterType(type))
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
     }
 
-    void IDisposable.Dispose()
+    bool ICascadingValueSupplier.CanSupplyValue(in CascadingParameterInfo parameterInfo)
+        => TryGetProvider(in parameterInfo, out var provider)
+        && provider.CanSupplyValue(_bindingContext, parameterInfo);
+
+    void ICascadingValueSupplier.Subscribe(ComponentState subscriber, in CascadingParameterInfo parameterInfo)
     {
-        Navigation.LocationChanged -= HandleLocationChanged;
+        // We expect there to always be a provider at this point, because CanSupplyValue must have returned true.
+        var provider = GetProviderOrThrow(parameterInfo);
+
+        if (!provider.AreValuesFixed)
+        {
+            provider.Subscribe(subscriber);
+        }
     }
 
-    bool ICascadingValueComponent.CanSupplyValue(Type valueType, string? valueName)
+    void ICascadingValueSupplier.Unsubscribe(ComponentState subscriber, in CascadingParameterInfo parameterInfo)
     {
-        var formName = string.IsNullOrEmpty(valueName) ?
-            (_bindingContext?.Name) :
-            ModelBindingContext.Combine(_bindingContext, valueName);
+        // We expect there to always be a provider at this point, because CanSupplyValue must have returned true.
+        var provider = GetProviderOrThrow(parameterInfo);
 
-        if (_bindingInfo != null &&
-            string.Equals(_bindingInfo.FormName, formName, StringComparison.Ordinal) &&
-            _bindingInfo.ValueType.Equals(valueType))
+        if (!provider.AreValuesFixed)
         {
-            // We already bound the value, but some component might have been destroyed and
-            // re-created. If the type and name of the value that we bound are the same,
-            // we can provide the value that we bound.
-            return true;
+            provider.Unsubscribe(subscriber);
         }
+    }
 
-        // Can't supply the value if this context is for a form with a different name.
-        if (FormValueSupplier.CanBind(formName!, valueType))
-        {
-            var bindingSucceeded = FormValueSupplier.TryBind(formName!, valueType, out var boundValue);
-            _bindingInfo = new BindingInfo(formName, valueType, bindingSucceeded, boundValue);
-            if (!bindingSucceeded)
-            {
-                // Report errors
-            }
+    object? ICascadingValueSupplier.GetCurrentValue(in CascadingParameterInfo parameterInfo)
+        => TryGetProvider(in parameterInfo, out var provider)
+            ? provider.GetCurrentValue(_bindingContext, parameterInfo)
+            : null;
 
-            return true;
+    private CascadingModelBindingProvider GetProviderOrThrow(in CascadingParameterInfo parameterInfo)
+    {
+        if (!TryGetProvider(parameterInfo, out var provider))
+        {
+            throw new InvalidOperationException($"No model binding provider could be found for parameter '{parameterInfo.PropertyName}'.");
         }
 
-        return false;
+        return provider;
     }
 
-    void ICascadingValueComponent.Subscribe(ComponentState subscriber)
+    private bool TryGetProvider(in CascadingParameterInfo parameterInfo, [NotNullWhen(true)] out CascadingModelBindingProvider? result)
     {
-        throw new InvalidOperationException("Form values are always fixed.");
-    }
+        var attributeType = parameterInfo.Attribute.GetType();
 
-    void ICascadingValueComponent.Unsubscribe(ComponentState subscriber)
-    {
-        throw new InvalidOperationException("Form values are always fixed.");
-    }
+        if (_providersByCascadingParameterAttributeType.TryGetValue(attributeType, out result))
+        {
+            return result is not null;
+        }
 
-    object? ICascadingValueComponent.CurrentValue => _bindingInfo == null ?
-        throw new InvalidOperationException("Tried to access form value before it was bound.") :
-        _bindingInfo.BoundValue;
+        // We deliberately cache 'null' results to avoid searching for the same attribute type multiple times.
+        result = FindProviderForAttributeType(attributeType);
+        _providersByCascadingParameterAttributeType[attributeType] = result;
+        return result is not null;
 
-    bool ICascadingValueComponent.CurrentValueIsFixed => true;
+        CascadingModelBindingProvider? FindProviderForAttributeType(Type attributeType)
+        {
+            foreach (var provider in ModelBindingProviders)
+            {
+                if (provider.SupportsCascadingParameterAttributeType(attributeType))
+                {
+                    return provider;
+                }
+            }
+
+            return null;
+        }
+    }
 
-    private record BindingInfo(string? FormName, Type ValueType, bool BindingResult, object? BoundValue);
+    void IDisposable.Dispose()
+    {
+        Navigation.LocationChanged -= HandleLocationChanged;
+    }
 }

src/Components/Components/src/Binding/CascadingModelBindingProvider.cs

@@ -0,0 +1,69 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.AspNetCore.Components.Rendering;
+
+namespace Microsoft.AspNetCore.Components.Binding;
+
+/// <summary>
+/// Provides values that get supplied to cascading parameters with <see cref="CascadingModelBinder"/>.
+/// </summary>
+public abstract class CascadingModelBindingProvider
+{
+    /// <summary>
+    /// Gets whether values supplied by this instance will not change.
+    /// </summary>
+    protected internal abstract bool AreValuesFixed { get; }
+
+    /// <summary>
+    /// Determines whether this instance can provide values for parameters annotated with the specified attribute type.
+    /// </summary>
+    /// <param name="attributeType">The attribute type.</param>
+    /// <returns><c>true</c> if this instance can provide values for parameters annotated with the specified attribute type, otherwise <c>false</c>.</returns>
+    protected internal abstract bool SupportsCascadingParameterAttributeType(Type attributeType);
+
+    /// <summary>
+    /// Determines whether this instance can provide values to parameters with the specified type.
+    /// </summary>
+    /// <param name="parameterType">The parameter type.</param>
+    /// <returns><c>true</c> if this instance can provide values to parameters with the specified type, otherwise <c>false</c>.</returns>
+    protected internal abstract bool SupportsParameterType(Type parameterType);
+
+    /// <summary>
+    /// Determines whether this instance can supply a value for the specified parameter.
+    /// </summary>
+    /// <param name="bindingContext">The current <see cref="ModelBindingContext"/>.</param>
+    /// <param name="parameterInfo">The <see cref="CascadingParameterInfo"/> for the component parameter.</param>
+    /// <returns><c>true</c> if a value can be supplied, otherwise <c>false</c>.</returns>
+    protected internal abstract bool CanSupplyValue(ModelBindingContext? bindingContext, in CascadingParameterInfo parameterInfo);
+
+    /// <summary>
+    /// Gets the value for the specified parameter.
+    /// </summary>
+    /// <param name="bindingContext">The current <see cref="ModelBindingContext"/>.</param>
+    /// <param name="parameterInfo">The <see cref="CascadingParameterInfo"/> for the component parameter.</param>
+    /// <returns>The value to supply to the parameter.</returns>
+    protected internal abstract object? GetCurrentValue(ModelBindingContext? bindingContext, in CascadingParameterInfo parameterInfo);
+
+    /// <summary>
+    /// Subscribes to changes in supplied values, if they can change.
+    /// </summary>
+    /// <remarks>
+    /// This method must be implemented if <see cref="AreValuesFixed"/> is <c>false</c>.
+    /// </remarks>
+    /// <param name="subscriber">The <see cref="ComponentState"/> for the subscribing component.</param>
+    protected internal virtual void Subscribe(ComponentState subscriber)
+        => throw new InvalidOperationException(
+            $"'{nameof(CascadingModelBindingProvider)}' instances that have non-fixed values must provide an implementation for '{nameof(Subscribe)}'.");
+
+    /// <summary>
+    /// Unsubscribes from changes in supplied values, if they can change.
+    /// </summary>
+    /// <remarks>
+    /// This method must be implemented if <see cref="AreValuesFixed"/> is <c>false</c>.
+    /// </remarks>
+    /// <param name="subscriber">The <see cref="ComponentState"/> for the unsubscribing component.</param>
+    protected internal virtual void Unsubscribe(ComponentState subscriber)
+        => throw new InvalidOperationException(
+            $"'{nameof(CascadingModelBindingProvider)}' instances that have non-fixed values must provide an implementation for '{nameof(Unsubscribe)}'.");
+}