Service in Blazor

How to make a service in balzor that can work in every module of the project including in RCL. For example: Have a project: ServiceTestBlazorServerApp, Few RCLs: MainRazorClassLibrary, UserRazorClassLibrary and so on... Service:

public class UserService
{
    private User? _CurrentUser;

    public User? CurrentUser
    {
        get { return _CurrentUser; }
        set { _CurrentUser = value; }
    }
    
    public class User
    { 
        public string Name { get; set; }
        public Guid SessionId { get; set; }
    }
}

I need service to be active in every module and if one module makes a change in Users data the change should be visible to every other module. But for each individual session data should be independent, clients should have their own sessions. I want the service to be usable the same way as it would be usable if I had just one project ServiceTestBlazorServerApp.

Put your UserService in a base library.

I've added an event and a setter method to control updating CurrentUser.

namespace Shared;
public class UserService
{
    public event EventHandler? UserChanged;

    public User? CurrentUser { get; private set; }

    public void UpdateUser(User user)
    {
        this.CurrentUser = user;
        this.UserChanged?.Invoke(this, new EventArgs());
    }

    public class User
    {
        public string Name { get; set; } = "-- Not Set --";
        public Guid SessionId { get; set; }
    }
}

You can then reference the base library and use it in your Razor libraries.

Note the injected service, and IDisposable implementation.

@using Shared;

@inject UserService UserService
@implements IDisposable

<h3>UserComponent</h3>

<div>User Name: @UserService.CurrentUser</div>

@code {
    protected override void OnInitialized()
        => this.UserService.UserChanged += this.OnUserChanged;

    public void Dispose()
        => this.UserService.UserChanged -= this.OnUserChanged;

    private void OnUserChanged(object? sender, EventArgs e)
        => this.StateHasChanged();
}

You then reference the shared library and add the Service to the actual deployment project:

// Add services to the container.
builder.Services.AddRazorPages();
builder.Services.AddServerSideBlazor();
builder.Services.AddSingleton<WeatherForecastService>();
builder.Services.AddScoped<UserService>();