How to fix InvalidOperationException: No service for type 'Microsoft.AspNetCore.Identity.UserManager'

The error InvalidOperationException: No service for type 'Microsoft.AspNetCore.Identity.UserManager[Microsoft.AspNetCore.Identity.IdentityUser]' has been registered typically occurs when you're trying to inject or use UserManager<IdentityUser> (or another identity-related service) in your ASP.NET Core application, but it's not properly registered in the dependency injection container.

Here are steps to fix 'no service for type 'microsoft.aspnetcore.identity.usermanager`1[microsoft.aspnetcore.identity.identityuser]' has been registered.' or 'invalidoperationexception: no service for type 'microsoft.aspnetcore.identity.signinmanager`1[microsoft.aspnetcore.identity.identityuser]' has been registered' in ASP.NET Core.

Ensure that ASP.NET Core Identity is properly set up

ASP.NET Core Identity services need to be registered in the DI container during application setup. Make sure you have configured Identity in the ConfigureServices method of Startup.cs (or Program.cs if using minimal hosting model):

In Startup.cs or Program.cs:

public void ConfigureServices(IServiceCollection services)
{
    // Other services...
    
    // Register ASP.NET Core Identity services
    services.AddIdentity<IdentityUser, IdentityRole>()
            .AddEntityFrameworkStores<ApplicationDbContext>()
            .AddDefaultTokenProviders();

    // Add other required services (e.g., ApplicationDbContext, etc.)
}

If you create a custom user class as shown below.

public class ApplicationUser : IdentityUser
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

Make sure that ApplicationDbContext is also registered, and that it's configured to use Entity Framework or another provider for storing user data.

services.AddIdentity<ApplicationUser, IdentityRole>()
    .AddEntityFrameworkStores<ApplicationDbContext>()
    .AddDefaultTokenProviders();

You need to replace ApplicationUser with your custom user model and ApplicationDbContext with your application's DbContext if you are using a custom user class.

Ensure UserManager<IdentityUser> is injected properly

Ensure that you have imported the necessary namespaces at the top of your files where UserManager is being used.

using Microsoft.AspNetCore.Identity;

If you're using a custom IdentityUser class (e.g., a class that extends IdentityUser), make sure to inject the UserManager<ApplicationUser> into the constructor of your class where you need it:

// asp net core usermanager
private readonly UserManager<ApplicationUser> _userManager;

public MyController(UserManager<ApplicationUser> userManager)
{
    _userManager = userManager;
}

You need to open the _LoginPartial.cshtml file

@using Microsoft.AspNetCore.Identity
@inject SignInManager<IdentityUser> SignInManager
@inject UserManager<IdentityUser> UserManager

Next, change to

@using Microsoft.AspNetCore.Identity
@inject SignInManager<ApplicationUser> SignInManager
@inject UserManager<ApplicationUser> UserManager

You also need to open all related files and then change IdentityUser to ApplicationUser.

Check the DbContext Configuration and ensure that your DbContext is configured correctly to work with Identity.

public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {
    }
}

By following these steps, you should be able to fix the "InvalidOperationException: No service for type 'Microsoft.AspNetCore.Identity.UserManager'" error in your ASP.NET Core application.