I am trying to build a minimal working example of a CircuitHandler in a Blazor server side application but none of the CircuitHandler methods are called. I feel like I’m missing something obvious.

I’m developing on macOS Sonoma 14.5 using the .NET SDK Arm64 version 8.0.7.

I have used the dotnet commandline tool (version 8.0.303) to create a new project:

dotnet new blazor -o CircuitHandlerApp

In file MyCircuitHandler.cs I have added a simple CircuitHandler implementation:

using Microsoft.AspNetCore.Components.Server.Circuits;

namespace CircuitHandlerApp;


public class MyCircuitHandler : CircuitHandler
{
    public MyCircuitHandler()
    {
        Console.WriteLine("Constructor called.");
    }

    public override Task OnCircuitOpenedAsync(Circuit circuit, CancellationToken cancellationToken)
    {
        Console.WriteLine("OnCircuitOpenedAsync called.");
        return base.OnCircuitOpenedAsync(circuit, cancellationToken);
    }

    public override Task OnConnectionUpAsync(Circuit circuit, 
        CancellationToken cancellationToken)
    {
        Console.WriteLine("OnConnectionUpAsync called.");
        return Task.CompletedTask;
    }

    public override Task OnConnectionDownAsync(Circuit circuit, 
        CancellationToken cancellationToken)
    {
        Console.WriteLine("OnConnectionDownAsync called.");
        return Task.CompletedTask;
    }

    public override Task OnCircuitClosedAsync(Circuit circuit, CancellationToken cancellationToken)
    {
        Console.WriteLine("OnCircuitClosedAsync called.");
        return base.OnCircuitClosedAsync(circuit, cancellationToken);   
    }
}

I have registered the handler in Program.cs like this:

...
builder.Services.AddRazorComponents()
    .AddInteractiveServerComponents();

builder.Services.AddSingleton<CircuitHandler,MyCircuitHandler>();

var app = builder.Build();
...

In my interpretation of the documentation and other sources that should be enough to see some of the CircuitHandler methods being called. But that does not happen when I run the application and connect to it in the browser.

Also the constructor of MyCircuitHandler only gets called when I directly inject the CircuitHandler into one of the components.

On Github I didn’t find any issues that sound similar to this problem and I would think that this feature is too essential that no one would have found a bug here before me. So it is probably more a configuration problem.

I have tried using the .NET 9 Preview but that didn’t work either.

Here’s the full Program.cs file:

using CircuitHandlerTest;
using CircuitHandlerTest.Components;
using Microsoft.AspNetCore.Components.Server.Circuits;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddRazorComponents()
    .AddInteractiveServerComponents(options =>
    {
        options.DetailedErrors = true;
    });
builder.Services.AddSingleton<CircuitHandler, MyCircuitHandler>();
var app = builder.Build();

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error", createScopeForErrors: true);
    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
    app.UseHsts();
}

app.UseHttpsRedirection();

app.UseStaticFiles();
app.UseAntiforgery();

app.MapRazorComponents<App>()
    .AddInteractiveServerRenderMode();

app.Run();