netcore: manually create a Logger without using LoggerFactory

Question

I'm creating a console logger using:

_log = new LoggerFactory().AddConsole().CreateLogger(this.GetType().Name);

Now I'm getting the following warning:

controllers\DummyController.cs(31,20): warning CS0618:
'ConsoleLoggerExtensions.AddConsole(ILoggerFactory)' is obsolete: 
'This method is obsolete and will be removed in a future version. The 
recommended alternative is AddConsole(this ILoggingBuilder builder).' 

I'm not in the context of a dependency injection container.

UPDATE: I also tried using DI like this:

var serviceProvider = new ServiceCollection()
    .AddLogging()
    .BuildServiceProvider();
var log = serviceProvider.GetService<ILogger>();
log.LogInformation("testing _log");

But I get the following error:

Error Message:                                                                                                                                                
  System.ArgumentNullException : Value cannot be null.                                                                                                         
Parameter name: logger                                                                                                                                        
Stack Trace:                                                                                                                                                  
   at Microsoft.Extensions.Logging.LoggerExtensions.Log(ILogger logger, LogLevel logLevel, EventId eventId, Exception exception, String message, Object[] args)                                                                                                                                                             
   at Microsoft.Extensions.Logging.LoggerExtensions.LogInformation(ILogger logger, String message, Object[] args)      

It seems I can't get the logger from the container

Answer 1

The interface has changed, so that you use a static Create() factory method on LoggerFactory, with a delegate that is passed in a configuration object that you configure the provider on. The factory can then be used to create loggers as before:

    ILogger<Program> logger = LoggerFactory
        .Create(logging => logging.AddConsole())
        .CreateLogger<Program>();
    logger.LogInformation("Hello World!");

While an application should usually use a host builder, this can be very useful in unit testing, as you can pass in a real logger that writes to the console (instead of a mock), and see the output in your test results.

This is taken from the simple walkthough example at: https://github.com/sgryphon/essential-logging/tree/master/examples/GettingStarted

There is also further examples that show how to configure via a host builder, and how to use the Microsoft high performance logging pattern.