Powershell Windows Form listbox selection validation - winforms

Question

I have created a powershell script using windows forms containing list boxes to run a cmd command (helps eliminate user-error and expedites process a bit). The only problem I run into is the command will still attempt to run even if an item is not selected on one of the forms I have populate. This can cause the script to simply not run, or it can cause mass amounts of data to be downloaded (the script pulls log files from a server, the listbox helps narrow down the data to be pulled). Is there a way to create error checking for the listbox that will essentially say "hey, you didn't select anything!" before continuing?
Thanks!
Edit (example of first list box):
$form = New-Object System.Windows.Forms.Form
$form.Text = "Select a production environment"
$form.Size = New-Object System.Drawing.Size(190,250)
$form.StartPosition = "CenterScreen"
$OKButton = New-Object System.Windows.Forms.Button
$OKButton.Location = New-Object System.Drawing.Point(10,180)
$OKButton.Size = New-Object System.Drawing.Size(75,23)
$OKButton.Text = "OK"
$OKButton.DialogResult = [System.Windows.Forms.DialogResult]::OK
$form.AcceptButton = $OKButton
$form.Controls.Add($OKButton)
$CancelButton = New-Object System.Windows.Forms.Button
$CancelButton.Location = New-Object System.Drawing.Point(85,180)
$CancelButton.Size = New-Object System.Drawing.Size(75,23)
$CancelButton.Text = "Cancel"
$CancelButton.DialogResult = [System.Windows.Forms.DialogResult]::Cancel
$form.CancelButton = $CancelButton
$form.Controls.Add($CancelButton)
$label = New-Object System.Windows.Forms.Label
$label.Location = New-Object System.Drawing.Point(10,20)
$label.Size = New-Object System.Drawing.Size(280,20)
$label.Text = "Please select a production environment:"
$form.Controls.Add($label)
$listBox = New-Object System.Windows.Forms.ListBox
$listBox.Location = New-Object System.Drawing.Point(10,40)
$listBox.Size = New-Object System.Drawing.Size(150,20)
$listBox.Height = 140
[void] $listBox.Items.Add("server1")
[void] $listBox.Items.Add("server2")
[void] $listBox.Items.Add("server3")
$form.Controls.Add($listBox)
$form.Topmost = $True
$result = $form.ShowDialog()
if ($result -eq [System.Windows.Forms.DialogResult]::OK)
{
$Prod = $listBox.SelectedItem
$Prod
}

Answer 1

There might be a way to perform this kind of validation using Windows Forms methods, but this uses PowerShell.
Perform $result = $form.ShowDialog() in a Do..Until or Do..While loop and continue showing the dialogue until the user has selected at least one item, and pressed OK - or the user exits the dialogue - else, show a warning and show the dialogue again.
Here is the relevant PowerShell code:
do
{
$result = $form.ShowDialog()
if ($ListBox.SelectedIndices.Count -lt 1 -and $result -eq [System.Windows.Forms.DialogResult]::OK)
{
Write-Warning 'Nothing was selected, please select a server.'
}
}
until (($result -eq [System.Windows.Forms.DialogResult]::OK -and $listBox.SelectedIndices.Count -ge 1) -or $result -ne [System.Windows.Forms.DialogResult]::OK)
Of course, you can replace Write-Warning with whatever you want, such as a message box.
PS: You can use the AddRange method to add an array of items to the $listBox collection, like so: [void] $listBox.Items.AddRange(#("server1", "server2", "server3"))