Support DI in SignalR.OpenApi example providers

Enable example providers to use constructor injection via DI. Update ReplyToMessageExamplesProvider to use IDateTimeProvider from DI. Add new DI-based example provider and hub for testing. Refactor SignalROpenApiDocumentGenerator to resolve providers using ActivatorUtilities. Add unit test to verify DI support in example providers.

Author: icnocop

samples/SignalR.OpenApi.Sample/Hubs/DateTimeProvider.cs

@@ -0,0 +1,12 @@
+// Copyright (c) SignalR.OpenApi Contributors. Licensed under the MIT License.
+
+namespace SignalR.OpenApi.Sample.Hubs;
+
+/// <summary>
+/// Provides the current local date and time.
+/// </summary>
+public class DateTimeProvider : IDateTimeProvider
+{
+    /// <inheritdoc/>
+    public DateTimeOffset Now() => DateTimeOffset.Now;
+}

samples/SignalR.OpenApi.Sample/Hubs/IDateTimeProvider.cs

@@ -0,0 +1,15 @@
+// Copyright (c) SignalR.OpenApi Contributors. Licensed under the MIT License.
+
+namespace SignalR.OpenApi.Sample.Hubs;
+
+/// <summary>
+/// Provides the current date and time.
+/// </summary>
+public interface IDateTimeProvider
+{
+    /// <summary>
+    /// Gets the current local date and time.
+    /// </summary>
+    /// <returns>The current local date and time as a <see cref="DateTimeOffset"/>.</returns>
+    DateTimeOffset Now();
+}

samples/SignalR.OpenApi.Sample/Hubs/ReplyToMessageExamplesProvider.cs

@@ -9,9 +9,22 @@ namespace SignalR.OpenApi.Sample.Hubs;
 /// </summary>
 public class ReplyToMessageExamplesProvider : ISignalROpenApiExamplesProvider<ReplyToMessageRequest>
 {
+    private readonly IDateTimeProvider dateTimeProvider;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ReplyToMessageExamplesProvider"/> class.
+    /// </summary>
+    /// <param name="dateTimeProvider">The date and time provider.</param>
+    public ReplyToMessageExamplesProvider(IDateTimeProvider dateTimeProvider)
+    {
+        this.dateTimeProvider = dateTimeProvider;
+    }
+
     /// <inheritdoc/>
     public IEnumerable<SignalROpenApiExample<ReplyToMessageRequest>> GetExamples()
     {
+        var now = this.dateTimeProvider.Now();
+
         yield return new SignalROpenApiExample<ReplyToMessageRequest>(
             "ReplyToGreeting",
             new ReplyToMessageRequest
@@ -20,13 +33,13 @@ public IEnumerable<SignalROpenApiExample<ReplyToMessageRequest>> GetExamples()
                 {
                     User = "Alice",
                     Message = "Hello, everyone!",
-                    Timestamp = new DateTimeOffset(2026, 2, 15, 10, 0, 0, TimeSpan.Zero),
+                    Timestamp = now,
                 },
                 Reply = new ChatMessage
                 {
                     User = "Bob",
                     Message = "Hi Alice, welcome!",
-                    Timestamp = new DateTimeOffset(2026, 2, 15, 10, 1, 0, TimeSpan.Zero),
+                    Timestamp = now,
                 },
             })
         {
@@ -41,13 +54,13 @@ public IEnumerable<SignalROpenApiExample<ReplyToMessageRequest>> GetExamples()
                 {
                     User = "Bob",
                     Message = "What time is the meeting?",
-                    Timestamp = new DateTimeOffset(2026, 2, 15, 14, 0, 0, TimeSpan.Zero),
+                    Timestamp = now,
                 },
                 Reply = new ChatMessage
                 {
                     User = "Alice",
                     Message = "It starts at 3 PM.",
-                    Timestamp = new DateTimeOffset(2026, 2, 15, 14, 2, 0, TimeSpan.Zero),
+                    Timestamp = now,
                 },
             })
         {

samples/SignalR.OpenApi.Sample/Program.cs

@@ -6,6 +6,7 @@
 
 var builder = WebApplication.CreateBuilder(args);
 
+builder.Services.AddSingleton<IDateTimeProvider, DateTimeProvider>();
 builder.Services.AddSignalR(options =>
 {
     options.EnableDetailedErrors = true;

src/SignalR.OpenApi.SwaggerUi/Resources/signalr-openapi-plugin.js

@@ -622,7 +622,8 @@ var SignalROpenApiPlugin = function (system) {
           return React.createElement(Original, props);
         };
       },
-      // Hide "No parameters" section for SignalR operations
+      // Hide "No parameters" message for SignalR operations while
+      // preserving the "Try it out" button that lives in this component.
       parameters: function (Original, system) {
         return function (props) {
           var React = system.React;
@@ -633,7 +634,9 @@ var SignalROpenApiPlugin = function (system) {
             var params = props.parameters;
             var count = params ? (params.size != null ? params.size : params.length) : 0;
             if (count === 0) {
-              return null;
+              return React.createElement("div", { className: "signalr-no-params" },
+                React.createElement(Original, props)
+              );
             }
           }
 

src/SignalR.OpenApi.SwaggerUi/Resources/signalr-openapi.css

@@ -58,6 +58,12 @@
   background: #e02020 !important;
 }
 
+/* Hide the "No parameters" message for SignalR operations
+   while keeping the "Try it out" button visible. */
+.signalr-no-params .opblock-description-wrapper .opblock-description {
+  display: none;
+}
+
 /* Client event log panel */
 .signalr-event-panel {
   font-family: sans-serif;

src/SignalR.OpenApi/Generation/SignalROpenApiDocumentGenerator.cs

@@ -5,6 +5,7 @@
 using System.Reflection;
 using System.Text.Json;
 using System.Text.Json.Serialization;
+using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Options;
 using Microsoft.OpenApi.Models;
 using SignalR.OpenApi.Examples;
@@ -1263,20 +1264,14 @@ private Dictionary<string, OpenApiExample> ResolveExamples(Type providerType)
     {
         var result = new Dictionary<string, OpenApiExample>();
 
-        // Try to resolve from DI first, then fall back to Activator.CreateInstance
-        object? provider = null;
+        // Create the provider using ActivatorUtilities, which resolves constructor
+        // dependencies from DI while allowing types that are not registered themselves.
+        object provider;
         try
         {
-            provider = this.serviceProvider.GetService(providerType);
+            provider = ActivatorUtilities.CreateInstance(this.serviceProvider, providerType);
         }
-        catch (InvalidOperationException)
-        {
-            // Provider not registered in DI
-        }
-
-        provider ??= Activator.CreateInstance(providerType);
-
-        if (provider is null)
+        catch (Exception)
         {
             return result;
         }
@@ -1339,19 +1334,12 @@ private Dictionary<string, OpenApiExample> ResolveExamplesForDerivedType(Type pr
     {
         var result = new Dictionary<string, OpenApiExample>();
 
-        object? provider = null;
+        object provider;
         try
         {
-            provider = this.serviceProvider.GetService(providerType);
-        }
-        catch (InvalidOperationException)
-        {
-            // Provider not registered in DI
+            provider = ActivatorUtilities.CreateInstance(this.serviceProvider, providerType);
         }
-
-        provider ??= Activator.CreateInstance(providerType);
-
-        if (provider is null)
+        catch (Exception)
         {
             return result;
         }
@@ -1438,19 +1426,12 @@ private Dictionary<string, OpenApiExample> ResolveExamplesForDerivedType(Type pr
 
     private object? GetFirstExampleValueFromProvider(Type providerType, Type? filterType = null)
     {
-        object? provider = null;
+        object provider;
         try
         {
-            provider = this.serviceProvider.GetService(providerType);
-        }
-        catch (InvalidOperationException)
-        {
-            // Provider not registered in DI
+            provider = ActivatorUtilities.CreateInstance(this.serviceProvider, providerType);
         }
-
-        provider ??= Activator.CreateInstance(providerType);
-
-        if (provider is null)
+        catch (Exception)
         {
             return null;
         }

test/SignalR.OpenApi.Tests/SignalROpenApiDocumentGeneratorTests.cs

@@ -1,5 +1,6 @@
 // Copyright (c) SignalR.OpenApi Contributors. Licensed under the MIT License.
 
+using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Options;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using SignalR.OpenApi.Discovery;
@@ -861,6 +862,49 @@ public void GenerateDocument_PolymorphicSubEndpoint_FormSchemaHasFilteredPropert
         Assert.IsNull(circleFormSchema.Properties["kind"].Example, "ReadOnly discriminator should not have an example.");
     }
 
+    /// <summary>
+    /// Verifies that examples providers with constructor dependencies are resolved via DI.
+    /// </summary>
+    [TestMethod]
+    public void GenerateDocument_ExamplesProviderWithDependencyInjection()
+    {
+        var services = new ServiceCollection();
+        services.AddSingleton<ITestValueProvider>(new TestValueProvider("InjectedProduct"));
+        using var serviceProvider = services.BuildServiceProvider();
+
+        var options = new SignalROpenApiOptions
+        {
+            Assemblies = [typeof(DiExampleHub).Assembly],
+        };
+
+        var opts = Options.Create(options);
+        var discoverer = new ReflectionHubDiscoverer(opts);
+        var generator = new SignalROpenApiDocumentGenerator(opts, serviceProvider);
+
+        var hubs = discoverer.DiscoverHubs();
+        var doc = generator.GenerateDocument(hubs);
+
+        var submitRequest = doc.Paths["/hubs/DiExample/SubmitRequest"]
+            .Operations[Microsoft.OpenApi.Models.OperationType.Post];
+
+        Assert.IsNotNull(submitRequest.RequestBody, "SubmitRequest should have a request body.");
+
+        var jsonContent = submitRequest.RequestBody.Content["application/json"];
+        Assert.IsNotNull(jsonContent.Examples, "Request body should have examples.");
+        Assert.IsTrue(jsonContent.Examples.ContainsKey("DiExample"), "Should contain 'DiExample' example.");
+
+        var diExample = jsonContent.Examples["DiExample"];
+        Assert.AreEqual("Example from DI provider", diExample.Summary);
+
+        // Verify the injected value was used
+        Assert.IsNotNull(diExample.Value, "Example value should not be null.");
+        var exampleObj = diExample.Value as Microsoft.OpenApi.Any.OpenApiObject;
+        Assert.IsNotNull(exampleObj, "Example value should be an OpenApiObject.");
+        var nameValue = exampleObj["name"] as Microsoft.OpenApi.Any.OpenApiString;
+        Assert.IsNotNull(nameValue, "Name property should exist.");
+        Assert.AreEqual("InjectedProduct", nameValue.Value, "Name should be the injected value.");
+    }
+
     private static (ReflectionHubDiscoverer Discoverer, SignalROpenApiDocumentGenerator Generator) CreateServices(
         Action<SignalROpenApiOptions>? configure = null)
     {
@@ -880,4 +924,16 @@ private sealed class EmptyServiceProvider : IServiceProvider
     {
         public object? GetService(Type serviceType) => null;
     }
+
+    private sealed class TestValueProvider : ITestValueProvider
+    {
+        private readonly string value;
+
+        public TestValueProvider(string value)
+        {
+            this.value = value;
+        }
+
+        public string GetValue() => this.value;
+    }
 }

test/SignalR.OpenApi.Tests/TestHubs/DiExampleHub.cs

@@ -0,0 +1,23 @@
+// Copyright (c) SignalR.OpenApi Contributors. Licensed under the MIT License.
+
+using Microsoft.AspNetCore.SignalR;
+using SignalR.OpenApi.Examples;
+
+namespace SignalR.OpenApi.Tests.TestHubs;
+
+/// <summary>
+/// A hub demonstrating DI-based example provider attributes.
+/// </summary>
+public class DiExampleHub : Hub
+{
+    /// <summary>
+    /// Submits a request using a DI-based examples provider.
+    /// </summary>
+    /// <param name="request">The request to submit.</param>
+    /// <returns>The request identifier.</returns>
+    [SignalROpenApiRequestExamples(typeof(DiOrderRequestExamplesProvider))]
+    public Task<string> SubmitRequest(DiRequest request)
+    {
+        return Task.FromResult("REQ-001");
+    }
+}

test/SignalR.OpenApi.Tests/TestHubs/DiOrderRequestExamplesProvider.cs

@@ -0,0 +1,33 @@
+// Copyright (c) SignalR.OpenApi Contributors. Licensed under the MIT License.
+
+using SignalR.OpenApi.Examples;
+
+namespace SignalR.OpenApi.Tests.TestHubs;
+
+/// <summary>
+/// An examples provider that requires a dependency injected via the constructor.
+/// </summary>
+public class DiOrderRequestExamplesProvider : ISignalROpenApiExamplesProvider<DiRequest>
+{
+    private readonly ITestValueProvider valueProvider;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="DiOrderRequestExamplesProvider"/> class.
+    /// </summary>
+    /// <param name="valueProvider">The test value provider.</param>
+    public DiOrderRequestExamplesProvider(ITestValueProvider valueProvider)
+    {
+        this.valueProvider = valueProvider;
+    }
+
+    /// <inheritdoc/>
+    public IEnumerable<SignalROpenApiExample<DiRequest>> GetExamples()
+    {
+        yield return new SignalROpenApiExample<DiRequest>(
+            "DiExample",
+            new DiRequest { Name = this.valueProvider.GetValue() })
+        {
+            Summary = "Example from DI provider",
+        };
+    }
+}