c# – Errors persist when rebuilding fixed .NET 9.0 Blazor web app (but not in Incognito)

I’ve loaded the Blazor web app template in Visual Studio, and I’m using .NET 9.0. I was doing some experimentation with dependency injection in order to try to get a good understanding of how that worked within Blazor.

I was able to create a simple DI scenario that worked, but then as I experimented, I introduced a bug that broke the DI. When I tried to retrace my steps, the original code no longer worked (except in Incognito mode). I made of a point of “Cleaning” my solution prior to build assuming there was some sort of rogue artifact causing problems, but the problem persisted.

It has me second-guessing my incremental changes that didn’t seem to work (was I running the code I thought I was, or was there something persisting that I wasn’t aware of?)

I don’t think the specifics of my code are particularly relevant, but I can give a bit of background. Basically, I created a ICounterService to use with the sample Counter page (in the WebClient.App project of the templated solution). I created a “variable” implementation of that which takes an integer in the constructor, and then a SingleStep version that inherits the variable implementation, but with a value of 1.

The CounterPage uses the service, then, to increment that counter value.

Modified Counter.razor:

@page "/counter"

@rendermode InteractiveWebAssembly

@inject ICountService CountService

<PageTitle>Counter</PageTitle>

<h1>Counter</h1>

<p role="status">Current count: @currentCount</p>

<button class="btn btn-primary" @onclick="IncrementCount">Click me</button>

@code {
    private int currentCount = 0;

    private void IncrementCount()
    {
        Console.WriteLine("Incrementing counter with count service...");
        currentCount = currentCount + CountService.GetStep();
    }
}

My dependency “Counter Service” components:

public interface ICountService
{
    int GetStep();
}

public class VariableCountService : ICountService
{
    protected int StepSize { get; set; }

    public VariableCountService(int stepSize)
    {
        StepSize = stepSize;
    }

    public int GetStep()
    {
        return StepSize;
    }

    public override string ToString()
    {
        return $"Variable Counter [{StepSize}]";
    }
}

public class SingleStepCountService : VariableCountService
{
    public SingleStepCountService()
        : base(1)
    { }

    public override string ToString()
    {
        return $"Single Step Counter";
    }
}

This is my Program.cs file:

    public class Program
    {
        public static void Main(string[] args)
        {
            var builder = WebApplication.CreateBuilder(args);

            // Add services to the container.
            builder.Services.AddRazorComponents()
                .AddInteractiveServerComponents()
                .AddInteractiveWebAssemblyComponents();

             // This WORKS
             builder.Services.AddScoped<ICountService, SingleStepCountService>();

             // This does NOT
             // builder.Services.AddSingleton<ICountService>(new VariableCountService(2));

            // This does NOT
            //var counter = new VariableCountService(2);
            //builder.Services.AddSingleton<ICountService>(counter);

            // This does NOT    
            //var counter = new VariableCountService(2);
            //builder.Services.AddSingleton<ICountService, VariableCountService>((x) => { return counter; });

            var app = builder.Build();

            // SNIP

            app.Run();
        }
    }
}

The code by the green arrow worked. I made incremental steps that didn’t (yellow), but when I rolled back, original no longer worked (except in Incognito)