处理WaitForSingleObject响应UI

Question

我使用以下代码来了解如何在流程处于活动状态时等待流程结束
在我的代码中，当记事本打开时，我会看到MessageBox。

如何在不使我的表单无响应的情况下等待记事本关闭？

Public Class Form1
Private Const WAIT_INFINITE = -1&
Private Const SYNCHRONIZE = &H100000
Private Declare Function OpenProcess Lib "kernel32" _
(ByVal dwDesiredAccess As Long,
ByVal bInheritHandle As Long,
ByVal dwProcessId As Long) As Long
Private Declare Function WaitForSingleObject Lib "kernel32" _
(ByVal hHandle As Long,
ByVal dwMilliseconds As Long) As Long
Private Declare Function CloseHandle Lib "kernel32" _
(ByVal hObject As Long) As Long
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim hProcess As Long
Dim taskId As Long
Dim cmdline As String
cmdline = "notepad.exe"
taskId = Shell(cmdline, vbNormalFocus)
hProcess = OpenProcess(SYNCHRONIZE, True, taskId)
Call WaitForSingleObject(hProcess, WAIT_INFINITE)
CloseHandle(hProcess)
MsgBox ("The shelled app has ended.")
End Sub
End Class

Answer 1

在.Net Framework/.Net Core中，您可以使用异步、事件驱动的WaitForExit版本，订阅Exited事件，该事件在您启动的进程终止时引发。

注意：事件在ThreadPool线程中引发。您可以将Process.SynchronizingObject设置为当前Form实例，以将事件封送至UI线程。

在.Net Framework中，将[Process].StartInfo.UseShellExecute设置为False，因为默认值为True
在.Net Core中，默认值已经是False。

引发事件时，进程已退出(HasExited为True(，因此并非所有常规信息都可用。Process.StartInfo(ProcessStartInfo对象(是可访问的，当然还有ExitTime和其他值(在引发事件时检查Process对象(。

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim p = New Process()
p.StartInfo.FileName = "notepad.exe"
p.StartInfo.UseShellExecute = False
p.SynchronizingObject = Me
p.EnableRaisingEvents = True
AddHandler p.Exited,
Sub()
Dim processName = p.StartInfo.FileName
Dim exitTime = p.ExitTime
p?.Dispose()
MessageBox.Show("Process exited")
DoSomethingElseRelated(processName, exitTime)
End Sub
p.Start()
End Sub

Answer 2

在最简单的情况下，WaitForExitAsync看起来像：

Private Async Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim p = Process.Start("notepad.exe")
Await p.WaitForExitAsync()
MsgBox ("The shelled app has ended.")
End Sub