处理 WaitForSingleObject - 响应式 UI

如何解决处理 WaitForSingleObject - 响应式 UI

我使用以下代码来了解如何在进程处于活动状态时等待进程结束。
在我的代码中，就在记事本打开时，我看到了 MessageBox。

如何等到记事本关闭，而不会使我的表单无响应？

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

解决方法

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：该事件在 ThreadPool 线程中引发。您可以将 Process.SynchronizingObject 设置为当前 Form 实例以将事件编组到 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。

当事件引发时，进程已经退出（HasExited 为 True），因此并非所有常用信息都可用。 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

,

最简单的，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