Cannot find the fallback endpoint specified by route values

1. Check Program.cs Configuration

Ensure that your app is correctly configured for Razor Pages and Blazor:

The MapFallbackToPage("/_Host") call tells the app to serve the Blazor application from the _Host.cshtml file when no other route matches.

• In Program.cs (for .NET 6 or higher):
  • Ensure the routing is set up like this:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.UseRouting();
app.MapBlazorHub();
app.MapFallbackToPage("/_Host");

app.Run();

2. Check _Host.cshtml File Path and Name

Make sure that the _Host.cshtml file exists in the Pages folder and is named exactly _Host.cshtml.

• It should be in the Pages folder by default:
  Pages/_Host.cshtml

• Ensure that it has the correct layout and content for a Blazor Server app or a Blazor WebAssembly app:

@page "/"
@namespace YourAppNamespace.Pages
@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
@{
    Layout = "_Layout";
}

//1



    ...


    Loading...

    



//or 2


//or 3

3. Ensure Razor Pages are Enabled

Verify that Razor Pages are enabled in your Program.cs:

• In Program.cs for .NET 6 or higher:

builder.Services.AddRazorPages();

4. Check Route Conflicts

Check if there is any routing conflict in your app (for example, an endpoint that matches /). If you're using MVC and Razor Pages, make sure you don't have conflicting routes.

5. Blazor Server or WebAssembly Specific Fixes

if you have added Blazor js script in _Host.cshtml file:

• Blazor Server: Ensure you have the proper signal for Blazor Server in your _Host.cshtml file:

• Blazor WebAssembly: Ensure your _Host.cshtml references the WebAssembly script:

6. Clear Build Cache

Sometimes build artifacts can cause issues. Try clearing the build cache:

• Clean the solution and rebuild it.
• Delete the bin and obj folders manually if needed.

Hi Gcobani,

It seems like you're encountering an issue with your Blazor app where it's throwing an InvalidOperationException due to not being able to find the fallback endpoint specified by route values.

From what I've gathered, this error can occur due to various reasons . Here are some potential solutions you can try:

Solution 1: Check for Preview/CTP Versions of .NET SDK

• Make sure you don't have any preview or CTP versions of the .NET SDK installed.
• If you do, try uninstalling them and see if that resolves the issue.

Solution 2: Verify SDK Version

• Ensure that you have the full version of the .NET SDK installed (in this case, SDK 7).
• If you're using a preview or CTP version, try installing the full version.

Solution 3: Check for Conflicting Visual Studio Versions

• If you have multiple versions of Visual Studio installed, try uninstalling any preview versions.
• This might resolve any conflicts that could be causing the issue.

If none of these solutions work, please provide more details about your project, such as the .NET SDK version and Visual Studio version you're using, and I'll do my best to help you troubleshoot the issue.