无法将参数传递给BackgroundWorker.RunWorkerAsync（System.MissingMemberException）

Question

我正在创建一个数据库作业执行程序，允许用户自动从各种API接口检索数据集，并将它们导入我们的数据库。

在应用程序启动时加载所有作业后，后台工作程序engine_JobTrigger启动一个循环，现在重复检查日期和时间，并将其与存储库中每个作业的NextExecutionTime进行比较。如果发生触发，后台线程会创建一个新的BackgroundWorker实例（必需以便可以触发其他作业启动），通过DoWork向Job.ExecuteJob添加处理程序，并开始执行工作程序：

'Class definition for Job Executor Engine
Public Class engine_JobExecutorArgs
        Public SourceJob As Job = Nothing
        Public ExecutedAs As String = ""
        Public ExecuteStartTime As DateTime = Nothing
End Class
.............................................

engine_JobTrigger.DoWork \|/
.............................................
While Not engine.Cancel = True
   Dim jobsToStart As New List(Of Integer)
   If JobController.Jobs.Count > 0 Then
       For Each process As Job In JobController.Jobs
           If process.Schedule.isNowNextExecutionTime(process.LastExecutionTime) And Not process.isExecuting Then jobsToStart.Add(process.JobID)
       Next
   End If

   If jobsToStart.Count > 0 Then
       For Each JobID As Integer In jobsToStart
           'Argument passed to BackgroundWorker
           Dim newJobExecutorArgs As New engine_JobExecutorArgs() With {
               .SourceJob = JobController.GetJob(CType(JobID, Integer)),
               .ExecutedAs = Security.Principal.WindowsIdentity.GetCurrent().Name.ToString(),
               .ExecuteStartTime = Now
           }
           Dim newJobExecutor As New System.ComponentModel.BackgroundWorker()
           AddHandler newJobExecutor.DoWork, AddressOf newJobExecutorArgs.SourceJob.ExecuteJob
           AddHandler newJobExecutor.RunWorkerCompleted, AddressOf engine_JobExecutor_RunWorkerCompleted

           newJobExecutor.RunWorkerAsync(newJobExecutorArgs)
       Next
   Else
       Threading.Thread.Sleep(200)
   End If

End While

一切顺利，直到我输入Job.ExecuteJob函数并尝试声明传递给新创建的BackgroundWorker的参数：

Dim inputArgs As MainWindow.engine_JobExecutorArgs = DirectCast(e.Argument(0), MainWindow.engine_JobExecutorArgs)

System.MissingMemberException
  HResult=0x80131512
  Message=No default member found for type 'engine_JobExecutorArgs'.
  Source=Microsoft.VisualBasic
  StackTrace:
   at Microsoft.VisualBasic.CompilerServices.Symbols.Container.GetMembers(String& MemberName, Boolean ReportErrors)
   at Microsoft.VisualBasic.CompilerServices.NewLateBinding.CallMethod(Container BaseReference, String MethodName, Object[] Arguments, String[] ArgumentNames, Type[] TypeArguments, Boolean[] CopyBack, BindingFlags InvocationFlags, Boolean ReportErrors, ResolutionFailure& Failure)
   at Microsoft.VisualBasic.CompilerServices.NewLateBinding.InternalLateIndexGet(Object Instance, Object[] Arguments, String[] ArgumentNames, Boolean ReportErrors, ResolutionFailure& Failure, Boolean[] CopyBack)
   at Microsoft.VisualBasic.CompilerServices.NewLateBinding.ObjectLateInvokeDefault(Object Instance, Object[] Arguments, String[] ArgumentNames, Boolean ReportErrors, Boolean[] CopyBack)
   at Microsoft.VisualBasic.CompilerServices.NewLateBinding.LateIndexGet(Object Instance, Object[] Arguments, String[] ArgumentNames)
   at Mastermind.Job.ExecuteJob(Object sender, DoWorkEventArgs e) in ...Mastermind\JobObject.vb:line 184
   at System.ComponentModel.BackgroundWorker.OnDoWork(DoWorkEventArgs e)
   at System.ComponentModel.BackgroundWorker.WorkerThreadStart(Object argument)

有人有什么建议吗？我希望继续使用类对象作为我的BackgroundWorkers的参数，这将在我完成后需要实现新功能时帮助我。在这种情况下，如何将自定义类作为参数传递给“RunWorkerAsync”？提前感谢您的任何建议！

编辑：一旦错误发生，我可以成功评估e.Argument(0)并通过IDE查看类中的值。

Answer 1

这是什么关于：

Dim inputArgs As MainWindow.engine_JobExecutorArgs = DirectCast(e.Argument(0), MainWindow.engine_JobExecutorArgs)

你为什么使用e.Argument(0)？ e.Argument只是一个Object引用，它指的是你传入的对象。你传入的对象是engine_JobExecutorArgs类型：

Dim newJobExecutorArgs As New engine_JobExecutorArgs()

'...

newJobExecutor.RunWorkerAsync(newJobExecutorArgs)

可以将该类型编入索引，即它是列表类型吗？不，不是，所以你期望索引它做什么？ e.Argument指的是该类型的对象，因此您应该将其转换为该类型：

Dim inputArgs As MainWindow.engine_JobExecutorArgs = DirectCast(e.Argument, MainWindow.engine_JobExecutorArgs)

没有索引要做，这是错误消息告诉你的。您正在尝试索引一个后期绑定的引用，它告诉您没有这样的成员。如果你有Option Strict On那么你会被告知不允许索引e.Argument，因为Object不是一个可索引类型。