Unable to resolve service for type 'Microsoft.Extensions.Logging.ILogger`1[WebApplication1.Startup]'

Question

I created an ASP.NET Core 3.0 Web Application with the default template in Visual Studio 2019 Preview 2.2 and tried to inject an ILogger in Startup:

namespace We         


        

Answer 1

If you want to log things after the Configure() has been called, you can still inject the ILogger via method injection (as opposed to the preferred constructor injection:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ILogger<TStartup> logger)
{
     _logger = logger;
     ...
}

Answer 2

This issue is related with IHostBuilder.

For a temp workaround, I suggest you try IWebHost to replace IHostBuilder.

Change your Program.cs like

public class Program
{
    public static void Main(string[] args)
    {           
        BuildWebHost(args).Run();
    }
    public static IWebHost BuildWebHost(string[] args) =>
            WebHost.CreateDefaultBuilder(args)
                .UseStartup<Startup>()
                .ConfigureLogging(logging =>
                {
                    logging.ClearProviders();
                    logging.AddConsole();
                })
                .Build();      
}

Answer 3

Did you have using ServiceCollection to register the Logger yet! It's should be here.

serviceProvider.AddTransient(typeof(ILogger<>), (typeof(Logger<>));

or you put, this is sample for Program.cs

public class Program  
{  
    public static void Main(string[] args)  
    {  
        BuildWebHost(args).Run();  
    }  

    public static IWebHost BuildWebHost(string[] args) =>  
        WebHost.CreateDefaultBuilder(args)  
            .ConfigureLogging(logging => logging.SetMinimumLevel(LogLevel.Warning))  
            .UseStartup<Startup>()  
            .Build();  
}  

Answer 4

This can be solved by registering the ILogger manually to use the Startup class as type.

Example:

public void ConfigureServices(IServiceCollection services)
{
    // Normal AddLogging
    services.AddLogging();

    // Additional code to register the ILogger as a ILogger<T> where T is the Startup class
    services.AddSingleton(typeof(ILogger), typeof(Logger<Startup>)); 
  
    // ...
}

Answer 5

Unfortunately, it's not possible to inject ILogger into Startup.cs in ASP.NET Core 3.0 anymore.

https://docs.microsoft.com/en-us/azure/azure-monitor/app/ilogger#capture-ilogger-logs-from-startupcs-and-programcs-in-aspnet-core-apps

Note

In ASP.NET Core 3.0 and later, it is no longer possible to inject ILogger in Startup.cs and Program.cs. See https://github.com/aspnet/Announcements/issues/353 for more details.