Asp.net core &引用';对象引用未设置为对象的实例;当我启动应用程序时
我有一些实现IHostedService的类 EmailSendService:Asp.net core &引用';对象引用未设置为对象的实例;当我启动应用程序时,asp.net-core,task,asp.net-core-3.1,asp.net-core-hosted-services,ihostedservice,Asp.net Core,Task,Asp.net Core 3.1,Asp.net Core Hosted Services,Ihostedservice,我有一些实现IHostedService的类 EmailSendService: public class EMailSendService : IHostedService, IDisposable { private Timer _timer; private IMailAccountService _mailAccountService; private IMailTaskDAL _mailTaskDal; private LoggerServiceBase
public class EMailSendService : IHostedService, IDisposable
{
private Timer _timer;
private IMailAccountService _mailAccountService;
private IMailTaskDAL _mailTaskDal;
private LoggerServiceBase _loggerServiceBase;
public EMailSendService(IMailAccountService mailAccountService, IMailTaskDAL mailTaskDal)
{
_mailAccountService = mailAccountService;
_mailTaskDal = mailTaskDal;
_loggerServiceBase = (LoggerServiceBase)Activator.CreateInstance(typeof(DatabaseLogger));
}
private void SendMail(object state)
{
var isAnyMailSended = false;
var logDetail = new LogDetail
{
UserID = "",
UserAgent = "",
IP = "System",
MethodName = "SENDMAILTASK",
StackTrace = "",
TraceIdentifier = ""
};
try
{
var now = DateTime.Now;
var mailTasks = _mailTaskDal.GetList(op => !op.IsSended && op.NextSendDate < now && op.TryCount < 10);
isAnyMailSended = mailTasks.Count > 0;
foreach (var mailTask in mailTasks)
{
var toList = mailTask.ToList.Split(',');
var sendResult = _mailAccountService.SendMail(toList, mailTask.Subject, mailTask.Body);
mailTask.Result = sendResult.Messages[0].Description;
if (sendResult.Success)
{
mailTask.IsSended = true;
mailTask.SendDate = DateTime.Now;
}
else
{
mailTask.NextSendDate = DateTime.Now.AddMinutes(5);
mailTask.TryCount++;
}
_mailTaskDal.Update(mailTask);
}
}
catch (Exception e)
{
logDetail.ExceptionMessage = e.Message;
logDetail.StackTrace = e.StackTrace;
}
finally
{
if (isAnyMailSended)
_loggerServiceBase.Info(logDetail);
}
}
public System.Threading.Tasks.Task StartAsync(CancellationToken cancellationToken)
{
_timer = new Timer(SendMail, null, TimeSpan.Zero, TimeSpan.FromSeconds(30));
return System.Threading.Tasks.Task.CompletedTask;
}
public System.Threading.Tasks.Task StopAsync(CancellationToken cancellationToken)
{
_timer?.Change(Timeout.Infinite, 0);
return System.Threading.Tasks.Task.CompletedTask;
}
public void Dispose()
{
_timer?.Dispose();
}
}
我使用两个扩展函数在startup.cs->ConfigureServices中添加此类:
services.AddHostedService<EMailSendService>();
services.AddHostedService<CreateActivityTask>();
services.AddHostedService();
services.AddHostedService();
但若我这样使用,程序就不会运行。启动时,此代码会抛出一个错误:
public class Program
{
public static void Main(string[] args)
{
CreateHostBuilder(args).Build().Run(); // This is where throws error
}
public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.UseServiceProviderFactory(new AutofacServiceProviderFactory())
.ConfigureWebHostDefaults(webBuilder =>
{
webBuilder.UseStartup<Startup>();
});
}
公共类程序
{
公共静态void Main(字符串[]args)
{
CreateHostBuilder(args).Build().Run();//这就是抛出错误的地方
}
公共静态IHostBuilder CreateHostBuilder(字符串[]args)=>
Host.CreateDefaultBuilder(args)
.UseServiceProviderFactory(新的AutofacServiceProviderFactory())
.ConfigureWebHostDefaults(webBuilder=>
{
webBuilder.UseStartup();
});
}
错误详细信息:
System.NullReferenceException
HResult=0x80004003
Message=Object reference not set to an instance of an object.
Source=Microsoft.Extensions.Hosting
StackTrace:
at Microsoft.Extensions.Hosting.Internal.Host.<StartAsync>d__9.MoveNext()
System.NullReferenceException
HResult=0x80004003
Message=对象引用未设置为对象的实例。
Source=Microsoft.Extensions.Hosting
堆栈跟踪:
在Microsoft.Extensions.Hosting.Internal.Host.d_u9.MoveNext()中
如果我评论
services.AddHostedService()
但我还是得到了错误。但是,如果我对所有“CreateActivityTask”类和“services.AddHostedService();”进行注释,那么我就可以运行该应用程序
EmailTaskService可以正常运行。但若我把“CreateActivityTask”单独留下(我的意思是,我对所有“EmailTaskService类等”都做了注释),程序会再次出错
我在CreateActivity类上看不到任何错误,因此我找不到错误所在。您能帮助我吗?根据您提供的代码,我们无法重现您的问题。如果可能,您可以提供有关您的代码的更多详细信息。我以不同的方式解决了此问题,谢谢大家。根据您提供的代码,我们无法重现您的问题eproduce你的问题。如果可能的话,你可以提供更多关于你的代码的细节。我用不同的方式解决了这个问题,谢谢大家。
System.NullReferenceException
HResult=0x80004003
Message=Object reference not set to an instance of an object.
Source=Microsoft.Extensions.Hosting
StackTrace:
at Microsoft.Extensions.Hosting.Internal.Host.<StartAsync>d__9.MoveNext()