Nivot Ink - Using Windows Forms Controls in PowerShell #1: ListBox

Sunday, December 02, 2007

Using Windows Forms Controls in PowerShell #1: ListBox

Using Windows Forms controls in PowerShell is a tricky thing, because it only supports very simple event handling. However, some time ago I wrote a Snap-In to allow anyone to work with .NET events, even asynchronous ones. You can download it from my PSEventing CodePlex project; it comes with full help via the normal PowerShell mechanisms of -? and get-help. Examples are also available online on how to use the project for more complex scenarios. Here's simple demonstration of autogenerating a listbox control filled with choices given as arguments to a simple script:

# as simple as 1,2,3
$choice = .\get-choice.ps1 "one","two","three"

And here is the source to the get-choice.ps1 script itself. This requires PSEventing 1.0 or 1.1 Beta.

#requires -pssnapin pseventing
# http://www.codeplex.com/pseventing (1.0 or 1.1)
param([string[]]$choices = $(throw "please supply a string array of choices"))
if ($choices.length -eq 0) {
Write-Warning "cannot be a zero length array."
return
}
# initialize form
$form = new-object windows.forms.form
$form.Text = "Choose..."
$form.MinimizeBox = $false
$form.MaximizeBox = $false
$form.AutoSize = $true
$form.AutoSizeMode = "GrowAndShrink"
# initialize listbox
$listbox = new-object windows.forms.listbox
$choices | % { [void]$listbox.items.add($_) }
$form.controls.Add($listbox)
# catch a choice in the listbox (remove -verbose for quiet mode)
Connect-EventListener -VariableName listbox -EventName SelectedIndexChanged -Verbose
# catch someone closing the form (remove -verbose for quiet mode)
Connect-EventListener -VariableName form -EventName Closed -Verbose
$form.Show()
# wait for an event while performing sendmessage pumping (or ctrl+c to exit)
$event = Get-Event -Wait
# don't pollute pipeline (remove in production)
write-host ($event | ft -auto | out-string)
$form.Dispose()
$choice = $listbox.SelectedItem
# clean up; event listeners will be automatically unhooked
$form = $null
$listbox = $null
# return chosen item, or $null if the form was closed
if ($event.Name -eq "SelectedIndexChanged") {
$choice
} else {
$null # cancelled
}

Have fun!