Ability to supply a pre-instantiated component as an API result (#12)

Author: SteveSandersonMS

src/Components/Samples/BlazorUnitedApp/Pages/FetchData.razor

@@ -41,8 +41,10 @@ else
 @code {
     WeatherForecast[]? forecasts;
 
+    [Parameter] public DateTime ForDate { get; set; } = DateTime.Now;
+
     protected override async Task OnInitializedAsync()
     {
-        forecasts = await ForecastService.GetForecastAsync(DateTime.Now);
+        forecasts = await ForecastService.GetForecastAsync(ForDate);
     }
 }

src/Components/Samples/BlazorUnitedApp/Program.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using BlazorUnitedApp.Data;
+using BlazorUnitedApp.Pages;
+using Microsoft.AspNetCore.Mvc.RazorPages;
 
 var builder = WebApplication.CreateBuilder(args);
 
@@ -29,4 +31,12 @@
 app.MapRazorComponents();
 app.MapBlazorHub();
 
+app.Map("/mycomponent", () =>
+{
+    return new RazorComponentResult
+    (
+        new FetchData { ForDate = DateTime.Now.AddYears(1000) }
+    );
+});
+
 app.Run();

src/Mvc/Mvc.RazorPages/src/PassiveComponentInstanceActivator.cs

@@ -0,0 +1,61 @@
+// 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;
+using Microsoft.Extensions.DependencyInjection;
+using System.Diagnostics.CodeAnalysis;
+
+namespace Microsoft.AspNetCore.Mvc.RazorPages;
+
+// This wraps any other registered component activator (or the default), adding the behavior
+// that a particular component instance can be pre-registered as the instance we'll use the
+// first time that component type is required.
+//
+// This is a hack to allow endpoints to return pre-constructed component instances and have
+// them inserted into the render tree inside their layouts, etc. For a real implementation,
+// this technique might not be too bad, or we might choose to change the renderer and diffing
+// system to have a concept of some whole new frame type describing pre-instantiated components.
+
+internal sealed class PassiveComponentInstanceActivator : IComponentActivator
+{
+    private readonly IComponentActivator _underlyingActivator;
+    private readonly IComponent? _componentInstance;
+    private Type? _componentInstanceType;
+
+    public PassiveComponentInstanceActivator(IServiceProvider requestServices, IComponent componentInstance)
+    {
+        _underlyingActivator = requestServices.GetService<IComponentActivator>()
+            ?? DefaultComponentActivator.Instance;
+        _componentInstanceType = componentInstance.GetType();
+        _componentInstance = componentInstance;
+    }
+
+    public IComponent CreateInstance([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type componentType)
+    {
+        // If it's the first time we're asked for the pre-supplied instance, supply it
+        if (componentType == _componentInstanceType)
+        {
+            _componentInstanceType = null;
+            return _componentInstance!;
+        }
+
+        // Otherwise fall back on the underlying implementation
+        return _underlyingActivator.CreateInstance(componentType);
+    }
+
+    // TODO: Instead of duplicating this code, put it somewhere we can share the type
+    internal sealed class DefaultComponentActivator : IComponentActivator
+    {
+        public static IComponentActivator Instance { get; } = new DefaultComponentActivator();
+
+        public IComponent CreateInstance([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type componentType)
+        {
+            if (!typeof(IComponent).IsAssignableFrom(componentType))
+            {
+                throw new ArgumentException($"The type {componentType.FullName} does not implement {nameof(IComponent)}.", nameof(componentType));
+            }
+
+            return (IComponent)Activator.CreateInstance(componentType)!;
+        }
+    }
+}

src/Mvc/Mvc.RazorPages/src/PassiveComponentRenderer.cs

@@ -36,9 +36,21 @@ public PassiveComponentRenderer(
         _htmlEncoder = htmlEncoder;
     }
 
-    public async Task HandleRequest(HttpContext httpContext, Type componentType, IReadOnlyDictionary<string, object?>? parameters)
+    public Task HandleRequest(HttpContext httpContext, IComponent componentInstance, IReadOnlyDictionary<string, object?>? parameters)
     {
-        using var htmlRenderer = new HtmlRenderer(httpContext.RequestServices, _loggerFactory, _viewBufferScope);
+        return HandleRequest(httpContext, componentInstance, componentInstance.GetType(), parameters);
+    }
+
+    public Task HandleRequest(HttpContext httpContext, Type componentType, IReadOnlyDictionary<string, object?>? parameters)
+    {
+        return HandleRequest(httpContext, null, componentType, parameters);
+    }
+
+    private async Task HandleRequest(HttpContext httpContext, IComponent? componentInstance, Type componentType, IReadOnlyDictionary<string, object?>? parameters)
+    {
+        using var htmlRenderer = componentInstance is null
+            ? new HtmlRenderer(httpContext.RequestServices, _loggerFactory, _viewBufferScope)
+            : new HtmlRenderer(httpContext.RequestServices, _loggerFactory, _viewBufferScope, new PassiveComponentInstanceActivator(httpContext.RequestServices, componentInstance));
         var staticComponentRenderer = new StaticComponentRenderer(htmlRenderer);
 
         var routeData = httpContext.GetRouteData();

src/Mvc/Mvc.RazorPages/src/PublicAPI.Unshipped.txt

@@ -10,8 +10,14 @@ Microsoft.AspNetCore.Mvc.RazorPages.PageBase.TryUpdateModelAsync<TModel>(TModel!
 Microsoft.AspNetCore.Mvc.RazorPages.PageModel.TryUpdateModelAsync<TModel>(TModel! model, string! name, Microsoft.AspNetCore.Mvc.ModelBinding.IValueProvider! valueProvider, params System.Linq.Expressions.Expression<System.Func<TModel!, object?>!>![]! includeExpressions) -> System.Threading.Tasks.Task<bool>!
 Microsoft.AspNetCore.Mvc.RazorPages.PageModel.TryUpdateModelAsync<TModel>(TModel! model, string! name, params System.Linq.Expressions.Expression<System.Func<TModel!, object?>!>![]! includeExpressions) -> System.Threading.Tasks.Task<bool>!
 Microsoft.AspNetCore.Mvc.RazorPages.RazorComponentResult
+Microsoft.AspNetCore.Mvc.RazorPages.RazorComponentResult.RazorComponentResult(Microsoft.AspNetCore.Components.IComponent! component) -> void
+Microsoft.AspNetCore.Mvc.RazorPages.RazorComponentResult.RazorComponentResult(Microsoft.AspNetCore.Components.IComponent! component, System.Collections.Generic.IReadOnlyDictionary<string!, object?>? parameters) -> void
 Microsoft.AspNetCore.Mvc.RazorPages.RazorComponentResult.RazorComponentResult(System.Type! componentType) -> void
 Microsoft.AspNetCore.Mvc.RazorPages.RazorComponentResult.RazorComponentResult(System.Type! componentType, System.Collections.Generic.IReadOnlyDictionary<string!, object?>? parameters) -> void
 Microsoft.AspNetCore.Mvc.RazorPages.RazorComponentResult.WithParameter(string! name, object? value) -> Microsoft.AspNetCore.Mvc.RazorPages.RazorComponentResult!
+Microsoft.AspNetCore.Mvc.RazorPages.RazorComponentResult<TComponent>
+Microsoft.AspNetCore.Mvc.RazorPages.RazorComponentResult<TComponent>.RazorComponentResult() -> void
+Microsoft.AspNetCore.Mvc.RazorPages.RazorComponentResult<TComponent>.RazorComponentResult(System.Collections.Generic.IReadOnlyDictionary<string!, object?>? parameters) -> void
+Microsoft.AspNetCore.Mvc.RazorPages.RazorComponentResult<TComponent>.RazorComponentResult(TComponent component, System.Collections.Generic.IReadOnlyDictionary<string!, object?>? parameters = null) -> void
 static Microsoft.AspNetCore.Builder.RazorComponentsEndpointRouteBuilderExtensions.AddRazorComponents(this Microsoft.Extensions.DependencyInjection.IServiceCollection! services) -> void
 static Microsoft.AspNetCore.Builder.RazorComponentsEndpointRouteBuilderExtensions.MapRazorComponents(this Microsoft.AspNetCore.Routing.IEndpointRouteBuilder! endpoints) -> void

src/Mvc/Mvc.RazorPages/src/RazorComponentResult.cs

@@ -1,6 +1,7 @@
 // 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;
 using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.DependencyInjection;
 
@@ -11,9 +12,10 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages;
 /// </summary>
 public class RazorComponentResult : IResult
 {
-    private readonly Type _componentType;
+    private readonly Type? _componentType;
     private readonly IReadOnlyDictionary<string, object?>? _parameters;
     private Dictionary<string, object?>? _modifiedParameters;
+    private readonly IComponent? _componentInstance;
 
     /// <summary>
     /// TODO
@@ -26,7 +28,25 @@ public RazorComponentResult(Type componentType)
     /// <summary>
     /// TODO
     /// </summary>
-    public RazorComponentResult(Type componentType, IReadOnlyDictionary<string, object?>? parameters) : this(componentType)
+    public RazorComponentResult(Type componentType, IReadOnlyDictionary<string, object?>? parameters)
+        : this(componentType)
+    {
+        _parameters = parameters;
+    }
+
+    /// <summary>
+    /// TODO
+    /// </summary>
+    public RazorComponentResult(IComponent component)
+    {
+        _componentInstance = component;
+    }
+
+    /// <summary>
+    /// TODO
+    /// </summary>
+    public RazorComponentResult(IComponent component, IReadOnlyDictionary<string, object?>? parameters)
+        : this(component)
     {
         _parameters = parameters;
     }
@@ -49,6 +69,37 @@ public RazorComponentResult WithParameter(string name, object? value)
     Task IResult.ExecuteAsync(HttpContext httpContext)
     {
         var renderer = httpContext.RequestServices.GetRequiredService<PassiveComponentRenderer>();
-        return renderer.HandleRequest(httpContext, _componentType, _modifiedParameters ?? _parameters);
+        var parameters = _modifiedParameters ?? _parameters;
+        return _componentInstance is not null
+            ? renderer.HandleRequest(httpContext, _componentInstance, parameters)
+            : renderer.HandleRequest(httpContext, _componentType!, parameters);
+    }
+}
+
+/// <summary>
+/// TODO
+/// </summary>
+public class RazorComponentResult<TComponent> : RazorComponentResult where TComponent : IComponent
+{
+    /// <summary>
+    /// TODO
+    /// </summary>
+    public RazorComponentResult() : base(typeof(TComponent))
+    {
+    }
+
+    /// <summary>
+    /// TODO
+    /// </summary>
+    public RazorComponentResult(IReadOnlyDictionary<string, object?>? parameters) : base(typeof(TComponent), parameters)
+    {
+    }
+
+    /// <summary>
+    /// TODO
+    /// </summary>
+    public RazorComponentResult(TComponent component, IReadOnlyDictionary<string, object?>? parameters = null)
+        : base(component, parameters)
+    {
     }
 }

src/Mvc/Mvc.ViewFeatures/src/RazorComponents/HtmlRenderer.cs

@@ -35,6 +35,13 @@ public HtmlRenderer(IServiceProvider serviceProvider, ILoggerFactory loggerFacto
         _serviceProvider = serviceProvider;
     }
 
+    public HtmlRenderer(IServiceProvider serviceProvider, ILoggerFactory loggerFactory, IViewBufferScope viewBufferScope, IComponentActivator componentActivator)
+        : base(serviceProvider, loggerFactory, componentActivator)
+    {
+        _viewBufferScope = viewBufferScope;
+        _serviceProvider = serviceProvider;
+    }
+
     public override Dispatcher Dispatcher { get; } = Dispatcher.CreateDefault();
 
     public ChannelReader<RenderBatch> StreamingRenderBatches { get; private set; }