Threads are the bane of my existence - vb.net

Question

I have a button which on click will run a Sub, creating a process which runs a script.
When this script is finished an Exited handler will fire and run another Sub which cleans up so that the application is ready to go anew without restarting it.
I disable the button during the run and try to re-enable it when the Exit is fired, however it tells me that the button is in another thread. So I tried using SynchronizedContext and Post:
Declared at the start of my class:
Class MainWindow
Private sc As SynchronizationContext = SynchronizationContext.Current
Not sure if I'm doing that correctly but it worked for me elsewhere in the code where I had the same problem.
The exit handling sub:
Private Sub CMD_Exited(ByVal sender As Object, ByVal e As EventArgs)
myProcess.CancelOutputRead()
myProcess.CancelErrorRead()
sc.Post(AddressOf Button_Click, Button1.IsEnabled = True)
Close()
End Sub
Which errors:
Method 'Private Sub Button_Click(sender As Object, e As RoutedEventArgs)' does not have a signature compatible with delegate 'Delegate Sub SendOrPostCallback(state As Object)'.
What can I do here? Changing the button signature will cause incompatibilities elsewhere.
Are there better ways to get around this threads issue?

Answer 1

Visual Vincent is correct, you need to invoke on the UI thread. Specifically you need to read this How to: Make Thread-Safe Calls to Windows Forms Controls.
Public Delegate Sub DoProcessStuffOnUIThreadHandler()
Private Sub CMD_Exited(ByVal sender As Object, ByVal e As EventArgs)
If Me.Button1.InvokeRequired Then
Dim d As New DoProcessStuffOnUIThreadHandler(AddressOf DoProcessStuffOnUIThread)
Me.Button1.Invoke(d)
Else
DoProcessStuffOnUIThread()
End If
End Sub
Private Sub DoProcessStuffOnUIThread()
myProcess.CancelOutputRead()
myProcess.CancelErrorRead()
Button1.IsEnabled = True
Close()
End Sub
(28-SEP-2017) Edit to add an alternative, that I used frequently in my WinForms code days, for brevity:
Public Delegate Sub DoProcessStuffOnUIThreadHandler()
Private Sub CMD_Exited(ByVal sender As Object, ByVal e As EventArgs)
If Me.Button1.InvokeRequired Then
Dim d As New DoProcessStuffOnUIThreadHandler(AddressOf CMD_Exited)
Me.Button1.Invoke(d)
Else
myProcess.CancelOutputRead()
myProcess.CancelErrorRead()
Button1.IsEnabled = True
Close()
End If
End Sub
The added example simply reduces code use. Both examples end in the same result. Hope that helps.