WaitForExit（）运行时异常。 （等待cmd进程完成） [英] WaitForExit() Runtime Exception. (Waiting for cmd process to finish)

问题描述

  Sub BtnNowClick（sender作为对象，作为EventArgs）
 
 Dim myProcess作为新进程
 Dim processFile As String = dlgFolder.SelectedPath 
 Dim pyLocationDel As String = Path.Combine（dlgFolder.SelectedPath， pdfmerge.py）
 
 Directory.SetCurrentDirectory（dlgFolder.SelectedPath）
 
 myProcess.Start（pyLocationDel）
 myProcess.WaitForExit（）
系统。 IO.File.Delete（pyLocationDel）
 
 
 End Sub 
  

基本上，我想要的是检测一个进程是否完成，如果进程完成，删除一个特定的文件。

以执行代码：

  System.NullReferenceException：对象引用未设置为对象的实例。 
 at lgaPDF.MainForm.BtnNowClick（Object sender，EventArgs e）in C：\Documents and Settings\student3\My Documents \SharpDevelop Projects\lgaPDF\lgaPDF\MainForm.vb：line 184 
在System.Windows.Forms.Control.OnClick（EventArgs e）
在System.Windows.Forms.Button.OnClick（EventArgs e）
在System.Windows.Forms.Button.OnMouseUp （MouseEventArgs mevent）
在System.Windows.Forms.Control.WmMouseUp（Message& m，MouseButtons按钮，Int32点击）
在System.Windows.Forms.Control.WndProc（Message& m）
 at System.Windows.Forms.ButtonBase.WndProc（Message& m）
在System.Windows.Forms.Button.WndProc（Message& m）
在System.Windows.Forms.Control.ControlNativeWindow .OnMessage（Message& m）
在System.Windows.Forms.Control.ControlNativeWindow.WndProc（Message& m）
在System.Windows.Forms.NativeWindow.DebuggableCallback（IntPtr hWnd，Int32 msg，IntPtr wparam，IntPtr lparam）
 at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW（MSG& msg）
在System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop（IntPtr dwComponentID，Int32原因，Int32 pvLoopData）
在System.Windows.Forms.Application .ThreadContext.RunMessageLoopInner（Int32原因，ApplicationContext上下文）
在System.Windows.Forms.Application.ThreadContext.RunMessageLoop（Int32原因，ApplicationContext上下文）
在Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun（） 
 at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel（）
 at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run（String [] commandLine）
 at lgaPDF.My.MyApplication.Main（String [] Args）in 17d14f5c-a337-4978-8281-53493378c1071.vb：line 81 
  

方案

因为你从不创建任何 Process 实例。

你声明的变量：

  Dim myProcess作为新进程（）
  

使用单独的构造函数调用：

  b $ b myProcess = New Process（）
  

Can you kindly tell me why I am getting a runtime exception when trying to run this code?

Sub BtnNowClick(sender As Object, e As EventArgs)

    Dim myProcess As New Process
    Dim processFile As String = dlgFolder.SelectedPath
    Dim pyLocationDel As String = Path.Combine(dlgFolder.SelectedPath, "pdfmerge.py")

    Directory.SetCurrentDirectory(dlgFolder.SelectedPath)

    myProcess.Start(pyLocationDel) 
    myProcess.WaitForExit()     
    System.IO.File.Delete(pyLocationDel)


End Sub

Basically, what I want, is to detect for a process to be finished and delete a specific file if the process is finished.

I'm getting this error when trying to execute the code:

   System.NullReferenceException: Object reference not set to an instance of an object.
   at lgaPDF.MainForm.BtnNowClick(Object sender, EventArgs e) in C:\Documents and Settings\student3\My Documents\SharpDevelop Projects\lgaPDF\lgaPDF\MainForm.vb:line 184
   at System.Windows.Forms.Control.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ButtonBase.WndProc(Message& m)
   at System.Windows.Forms.Button.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
   at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
   at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
   at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun()
   at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel()
   at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(String[] commandLine)
   at lgaPDF.My.MyApplication.Main(String[] Args) in 17d14f5c-a337-4978-8281-53493378c1071.vb:line 81

解决方案

Because you never create any Process instance.

You can use the constructor when you declare the varaible:

Dim myProcess As New Process()

With a separate constructor call:

Dim myProcess As Process
myProcess = New Process()

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