Blazor WebAssembly InvalidCastException when running Published version on IIS

Question

I have a Blazor WebAssembly application that works fine when debugging, but throws an exception when running on IIS (Published):

blazor.webassembly.js:1 crit: Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer[100]
      Unhandled exception rendering component: Specified cast is not valid.
System.InvalidCastException: Specified cast is not valid.
   at Microsoft.AspNetCore.Components.Reflection.MemberAssignment.GetPropertiesIncludingInherited(Type , BindingFlags )+MoveNext()
   at Microsoft.AspNetCore.Components.ComponentFactory.CreateInitializer(Type )
   at Microsoft.AspNetCore.Components.ComponentFactory.PerformPropertyInjection(IServiceProvider , IComponent )
   at Microsoft.AspNetCore.Components.ComponentFactory.InstantiateComponent(IServiceProvider , Type )
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.InstantiateComponent(Type )
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.InstantiateChildComponentOnFrame(RenderTreeFrame& , Int32 )
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.InitializeNewComponentFrame(DiffContext& , Int32 )
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.InitializeNewSubtree(DiffContext& , Int32 )
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.InsertNewFrame(DiffContext& , Int32 )
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.AppendDiffEntriesForRange(DiffContext& , Int32 , Int32 , Int32 , Int32 )
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.ComputeDiff(Renderer , RenderBatchBuilder , Int32 , ArrayRange`1 , ArrayRange`1 )
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder , RenderFragment , Exception& )
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.RenderInExistingBatch(RenderQueueEntry )
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessRenderQueue()

This error is quite useless i.m.o, as I can not find the exact cause, rather than it being an invalid cast exception.

Because debugging is not possible on published IIS site, I added Console.WriteLine to the Program.cs and the first Index.razor. However, the error occurs before the Index.razor is being rendered. And all code in my Program.main before the await builder.Build().RunAsync(); call works fine as well.

So I suppose it has something to do with my App.razoror MainLayout.razor. Now the MainLayout.razor is located inside a Razor Class Library with namespace Libs.Blazor.Components.Shared.

Program.cs

  /// <summary>
  /// Program entry
  /// </summary>
  public class Program {

    /// <summary>
    /// Entry point of application
    /// </summary>
    /// <param name="args">Arguments to pass</param>
    /// <returns>Task with a result</returns>
    public static async Task Main (String[] args) {
      var builder = WebAssemblyHostBuilder.CreateDefault(args);
      builder.RootComponents.Add<App>("#app");
      builder.RootComponents.Add<HeadOutlet>("head::after");

      HttpClient http = new HttpClient() {
        BaseAddress = new Uri(builder.HostEnvironment.BaseAddress)
      };

      IHostEnvironment hostEnvironment = new HostEnvironment() {
        ApplicationName = builder.HostEnvironment.Environment,
        EnvironmentName = builder.HostEnvironment.Environment,
        ContentRootPath = builder.HostEnvironment.Environment
      };

      builder.Services.AddScoped(sp => http);
      builder.Services.AddScoped(sp => hostEnvironment);

      using HttpResponseMessage response = await http.GetAsync("appsettings.json"); //Load the appsettings
      using Stream stream = await response.Content.ReadAsStreamAsync();

      builder.Configuration.AddJsonStream(stream);
      await builder.Build().RunAsync();
    } // Main

    /// <summary>
    /// HotEnvironment filled by WebAssembly
    /// </summary>
    internal class HostEnvironment :IHostEnvironment {
      private String m_EnvironmentName;
      private String m_ApplicationName;
      private String m_ContentRootPath;
      private IFileProvider m_ContentRootFileProvider;

      /// <summary>
      /// EnvironmentName
      /// </summary>
      public String EnvironmentName { [DebuggerStepThrough()] get { return m_EnvironmentName; } set { m_EnvironmentName = value; } }

      /// <summary>
      /// ApplicationName
      /// </summary>
      public String ApplicationName { [DebuggerStepThrough()] get { return m_ApplicationName; } set { m_ApplicationName = value; } }

      /// <summary>
      /// ContentRootPath
      /// </summary>
      public String ContentRootPath { [DebuggerStepThrough()] get { return m_ContentRootPath; } set { m_ContentRootPath = value; } }

      /// <summary>
      /// FileProvider
      /// </summary>
      public IFileProvider ContentRootFileProvider { [DebuggerStepThrough()] get { return m_ContentRootFileProvider; } set { m_ContentRootFileProvider = value; } }
    } // Class HostEnvironment
  } // Class Program

App.razor

<Router AppAssembly="@typeof(Program).Assembly" AdditionalAssemblies="new[] { typeof(Libs.Blazor.Components.Shared.MainLayout).Assembly }">
  <Found Context="routeData">
    <RouteView RouteData="@routeData" DefaultLayout="@typeof(Libs.Blazor.Components.Shared.MainLayout)" />
  </Found>
  <NotFound>
    <LayoutView Layout="@typeof(Libs.Blazor.Components.Shared.MainLayout)">
      <p>Sorry, there's nothing at this address.</p>
    </LayoutView>
  </NotFound>
</Router>

Libs.Blazor.Components.Shared.MainLayout

@namespace Libs.Blazor.Components.Shared
@inherits LayoutComponentBase

<body id="LibsBody" class="LibsBody" style="cursor:default;">
  @Body
  <div id="LibsHidden"></div>
</body>

So I am quite confused why I get this Invalid Cast Exception running the application on IIS, but not when I debug it in VS.

Answer 1

By accident I solved this issue by having a look at the Publish Profiles. Somehow the target runtime was set to Portable, instead of the required browser-wasm.

Answer 2

I had this same problem. The steps that worked for me to resolve were installing the .net 6 hosting bundle on the Windows Server hosting IIS. I then rebooted the IIS server and republished my application from VS2022. Now everything is working. Hope this helps.