Unable to clear or reset a listbox - windows

Question

I'm having trouble clearing a listbox that I created in my PowerShell form. If I call the listbox.Item.Clear method, the data stored in the listbox object is cleared but the items displayed in the from remain. Even after I try to create a new, blank listbox, the old items are still displayed. The listbox is created in a function that is called by a button click. I want the listbox to be cleared and repopulated each time the button is clicked. I can easily clear and re-add text to a text box by doing something like $textbox.Text = "new text". Is there a way to do this with a listbox? Here's what I have:
function AddMembers() {
Add-Type -AssemblyName System.Windows.Forms
Add-Type -AssemblyName System.Drawing
$form = New-Object System.Windows.Forms.Form
$form.Text = 'Select a Computer'
$form.Size = New-Object System.Drawing.Size(610,450)
$form.StartPosition = 'CenterScreen'
# Create the TextBox used to capture the user's text.
$textBox = New-Object System.Windows.Forms.Textbox
$textBox.Location = '10,40'
$textBox.Size = '375,170'
$textBox.AcceptsReturn = $true
$textBox.Multiline = $true
#$textBox.Text = $UserInputData
$form.Controls.Add($textBox)
function Global:GetTheSearchString() {
# If any text is present in the text box, convert it to a sting, parse, then conver to array $Global:UserInput2
$UserInput = $textBox.ToString()
$UserInput = $UserInput -replace "System.Windows.Forms.TextBox, Text: "
$Global:UserInput2 = $UserInput -split "`r`n"
Write-Host $Global:UserInput2
$InputLength = $UserInput2.Length
Write-Host $InputLength
$Global:lastLine = $UserInput2[$InputLength -1]
Write-Host "$Global:lastLine lastLine"
#return $Global:lastLine
}
# Take an input string, search AD, and return the results as an array.
function Global:SearchAD($SearchString) {
$Groups = Get-ADObject -LDAPFilter "(cn=$SearchString*)" | select Name | Out-String
$Groups = $Groups -replace "Name"
$Groups = $Groups -replace "----"
$Groups = $Groups.Trim()
$GroupsArray = $Groups -split "`r`n"
#Write-Host $GroupsArray
return $GroupsArray
}
# Create the list box for displaying search results
function CreateListBoxResults($searchResults, $param) {
$listBox = New-Object System.Windows.Forms.ListBox
#$form.Controls.Add($listBox)
#$listBox.Items.Clear()
#$listBox = New-Object System.Windows.Forms.ListBox
$listBox.Location = New-Object System.Drawing.Point(10,225)
$listBox.Size = New-Object System.Drawing.Size(375,20)
$listBox.Height = 150
# Add values to the list box
foreach ($line in $searchResults) {
[void] $listBox.Items.Add($line)
Write-Host $line
}
#$listBox.Refresh()
$form.Controls.Add($listBox)
Write-Host "$param param"
#Write-Host "$listBox listbox"
$form.Controls.Add($listBox)
if ($param -eq $true) {
Write-Host "$param param"
$listBox.Dispose()
$listBox.Items.Clear()
$form.Controls.Add($listBox)
}
}
#$selectButton.Add_Click({ [string]$selection = $listBox.SelectedItem.ToString(); Write-Host $selection; Global:ResetSearchBox($selection)})
#$selectButton.Add_Click({ Write-Host $Global:listBox; $click = $true; $Global:listBox.Items.Clear(); $form.Controls.Remove($Global:listBox); $form.Controls.Add($Global:listBox)})
Write-Host $UserInput2
$checkButton = New-Object System.Windows.Forms.Button
$checkButton.Location = New-Object System.Drawing.Point(9,380)
$checkButton.Size = New-Object System.Drawing.Size(85,23)
$checkButton.Text = 'Check Name'
$form.Controls.Add($checkButton)
$checkButton.Add_Click({ Global:GetTheSearchString; Write-Host "$Global:lastLine check"; CreateListBoxResults (Global:SearchAD($Global:lastLine)) $false })
$selectButton = New-Object System.Windows.Forms.Button
$selectButton.Location = New-Object System.Drawing.Point(102,380)
$selectButton.Size = New-Object System.Drawing.Size(75,23)
$selectButton.Text = 'Select'
$form.Controls.Add($selectButton)
$selectButton.Add_Click({ CreateListBoxResults $nul $true})
#$form.Controls.Add($listBox)
$form.Topmost = $true
$form.Add_Shown({$form.Activate()})
$form.ShowDialog() > $nul
}
AddMembers

Answer 1

For clearing the listbox you are right in using listbox.Item.Clear().
However there are some other usefull methods:
$listBox.Dispose()
The Dispose method leaves the Component in an unusable state. (You might not want this one.)
$form.Controls.Remove($listBox)
Remove your listbox from the form instead of deleting the object.
$listBox.Visible = $false (or $true)
Hide your listbox instead of removing it
$listBox.Items.Clear()
$listBox.Items.AddRange(*SomeArrayHere*)
The closest you can get to $textbox.text = "NewText"
Using some of these your function could look something like this:
function CreateListBoxResults($searchResults, $param) {
# Only create a listbox if it doesn't exist
if (!$listBox) {
$listBox = New-Object System.Windows.Forms.ListBox
$listBox.Location = New-Object System.Drawing.Point(10,225)
$listBox.Size = New-Object System.Drawing.Size(375,20)
$listBox.Height = 150
}
# Add listbox to form
$form.Controls.Add($listBox)
# Add values to the list box
$listBox.Items.Clear()
foreach ($line in $searchResults) {
[void] $listBox.Items.Add($line)
Write-Host $line
}
# Remove listbox from form if $param = $true
Write-Host "$param param"
if ($param -eq $true) {
Write-Host "$param param"
$form.Controls.Remove($listBox)
}
}