abp/templates/wpf/src/MyCompanyName.MyProjectName/HelloWorldService.cs

using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using Volo.Abp.DependencyInjection;

namespace MyCompanyName.MyProjectName;

public class HelloWorldService : ITransientDependency
{
    public ILogger<HelloWorldService> Logger { get; set; }

    public HelloWorldService()
    {
        Logger = NullLogger<HelloWorldService>.Instance;
    }
    public string SayHello()
    {
        Logger.LogInformation("Call SayHello");
        return "Hello world!";
    }
}