trouble with responsive form

[monderick]

i went through the 'creating responsive forms' blog post and have a 99% working script but cannot find where to insert the $script:timer.Stop() to reset the loop in the below listbox snippet.
the function updates the richtextbox and loop works great but locks the GUI.

if i write the same function for generic System.Windows.Forms it all works as expected so i don't know if Powershell Studio handles it differently.
thanks for any guidance on this, driving me crazy for some time now

Code: [Select all] [Expand/Collapse] [Download] (Untitled.ps1)

1. $listbox1_SelectedIndexChanged = {
2.     $workstation= $listbox1.SelectedItem
3.     $script:timer = New-Object System.Windows.Forms.Timer
4.     $script:timer.Interval = 1000
5.     $script:timer.Add_Tick({
6.             CheckStatus
7.         })
8.     $script:timer.Start()
9. }
10.  
11. function CheckStatus
12. {
13.     $job = Start-Job -ScriptBlock {
14.         $workstation = $Using:workstation
15.         Invoke-Command -computer *redacted* -ScriptBlock { Get-BrokerMachine -MaxRecordCount 2000 | ?{ $_.PublishedName -eq "$Using:workstation" } }
16.     }
17.         $job | wait-job | receive-job -outvariable status
18.        
19.     if ($status.registrationstate -eq 'Registered')
20.          {
21.         $richtextbox1.ForeColor = 'Green'
22.         $richtextbox1.Text = "$workstation is registered and should be available"
23.         }
24.     else
25.     {
26.         $richtextbox1.ForeColor = 'Red'
27.         $richtextbox1.Text = "$workstation is rebooting or not responding."
28.     }
29.  
30. }

if i just put $script:timer.Stop() at the end of listbox1_SelectedIndexChanged block, it errors:

ERROR: You cannot call a method on a null-valued expression.
Power cycle WVM.psf (181, 1): ERROR: At Line: 181 char: 1
ERROR: + $script:timer.Stop()
ERROR: + ~~~~~~~~~~~~~~~~~~~~
ERROR: + CategoryInfo : InvalidOperation: (:) [], RuntimeException
ERROR: + FullyQualifiedErrorId : InvokeMethodOnNull
ERROR:
ERROR: You cannot call a method on a null-valued expression.