Windows 服务 NullReferenceException C# [英] Windows Service NullReferenceException C#

问题描述

我正在尝试创建 Web API 服务，但是当我尝试作为服务运行时，我收到 NullReferenceException.如果我删除 ServiceBase 部分，它运行良好.如果我将 Thread 替换为什么都不做，那么它会照常工作.

I'm trying to create a Web API service but when I'm trying to run as service I get NullReferenceException. It's working well if I remove the ServiceBase part. If I replace the Thread to do nothing, then it's working as usual.

什么可能导致 NullReferenceException?

namespace WebApi
{
    public class Program
    {
        public static void Main(string[] args)
        {
            //To Debug
             //BuildWebHost(args).Run();

             //To Run as Service 
             using (var service = new TestService())
             {
                ServiceBase.Run(service);
             }
        }

        public static IWebHostBuilder BuildWebHost(string[] args) =>
            WebHost.CreateDefaultBuilder(args)
                .UseStartup<Startup>()
                .UseUrls("http://localhost:5000");

    }
}

class TestService : ServiceBase
    {
        public TestService()
        {
            ServiceName = "TestService";
        }

        protected override void OnStart(string[] args)
        {
            string filename = CheckFileExists();
            File.AppendAllText(filename, $"{DateTime.Now} started.{Environment.NewLine}");            
            Thread t = new Thread(new ThreadStart(Program.BuildWebHost(args).Build().Run));
            t.Start();
        }

        protected override void OnStop()
        {
            string filename = CheckFileExists();
            File.AppendAllText(filename, $"{DateTime.Now} stopped.{Environment.NewLine}");
        }

        private static string CheckFileExists()
        {
            string filename = @"c:\tmp\MyService.txt";
            if (!File.Exists(filename))
            {
                File.Create(filename);
            }

            return filename;
        }

    }

推荐答案

通过代码很难找到 NullReferene.但是您可以使用以下方法使其可调试:

It is hard to find the NullReferene by code. But you can make it debuggable with the following approach:

var s1 = new TestService();
if (!Environment.UserInteractive)
    ServiceBase.Run(new ServiceBase[] { s1 }); // when running as service
else
{
    s1.Start(args); // when running as console
    Console.ReadLine();
    s1.Stop();
}

这将作为 Windows 服务或控制台应用程序启动.

this will start as windows service or console application.

把这段代码放到Program.Main方法中并在debug下运行.

Put this code to the Program.Main method and run under debug.

PS 有 Topshelf library 也可以为您处理这些东西(将应用程序作为服务或控制台运行).

PS there is Topshelf library also that can deal this stuff for you (run application as service or console).

PPS 似乎您需要添加 public void TestService.Start 方法才能使此 UserInteractive 方法有效:

PPS seems that you will need to add public void TestService.Start method to make this UserInteractive approach works:

public class TestService : ServiceBase
{
  // existing code

  public void Start(string[] args)
  {
    OnStart(args);
  }

  public void Stop()
  {
    OnStop();
  }
}

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