Powershell GUI, Progress Bar, and Hash Tables - multithreading

Question

Part of a script that I'm working on takes the specified username, searches active directory for computers named like the username, pings them, and then adds the online machines to an array for use later. I'd like to add a progress bar to the ping portion of the script but I'm running into problems. The form I have to present the progress bar freezes execution of the script if I invoke it prior to the ping loop.
Here is the code for the progress bar (pretty basic):
#Progress Bar
$objFormPBar = New-Object System.Windows.Forms.Form
$objFormPBar.Text = "Loading"
$objFormPBar.Size = New-Object System.Drawing.Size(200,100)
$objFormPBar.StartPosition = "CenterScreen"
$objFormPBar.Topmost = $True
$objFormPBar.Icon = $Icon
$progressBar = New-Object System.Windows.Forms.ProgressBar
$progressBar.Size = New-Object System.Drawing.Size(175,20)
$progressBar.Location = New-Object System.Drawing.Size(5, 20)
$progressBar.Minimum = 0
$progressBar.Maximum = 0
$objFormPBar.Controls.Add($progressBar)
Here is where I'm attempting to display it, this way halts execution of the script (called from inside a click handler function, thus the global variables):
$global:progressBar.Maximum = $computers.count
$global:objFormPBar.Add_Shown({$objFormPBar.Activate()})
[void] $global:objFormPBar.ShowDialog()
Foreach ($computer in $computers) {
$computer = $computer.trim()
If(Test-Connection $computer -Count 1) {
$arrayComputers.add($computer) | Out-Null
}
$global:progressBar.Increment(1)
}
$global:objFormPBar.Close()
Looking into the problem I've discovered that you can run the progress bar in a separate thread and pass variables between the two (See: Marquee Progress Bar freezes in Powershell ). However I have had no luck getting it to work or even to get another thread to launch. How can I get this progress bar and the form along with it to run in another thread?

Answer 1

Why don't you just use the built-in UI for reporting progress in PowerShell? It's a one line call to Write-Progress e.g.:
$computers = 1..10 | % {"server$_"}
$numComputers = $computers.Length
for ($ndx = 0; $ndx -le $numComputers; $ndx++) {
$computer = $computers[$ndx].Trim()
Write-Progress "Testing connection to $computer" -PercentComplete ($ndx/$numComputers * 100)
#if (Test-Connection $computer -Count 1) {
# $arrayComputers.add($computer) | Out-Null
#}
Start-Sleep -Seconds 1
}
BTW the primary problem with your approach above is that the ShowDialog() method call doesn't return until the form is closed. If you want to use ShowDialog(), you have to execute your logic in the context of an event handler inside the form (Load/Activate). The other option is to use Show() but that means you'll have to pump messages in your loop using Application.DoEvents() so the form will have a chance to update itself.