Public/Get-WFListBoxItem.ps1

function Get-WFListBoxItem
{
<#
    .SYNOPSIS
        Function to get item(s) from a ListBox Control
     
    .DESCRIPTION
        Function to get item(s) from a ListBox Control
     
    .PARAMETER ListBox
        Specifies the ListBox control to get
     
    .PARAMETER SelectedItem
        Show only the selected Item
     
    .PARAMETER All
        Show all the item
     
    .EXAMPLE
        Get-WFListBoxItem -ListBox $ListBox1
     
    .EXAMPLE
        Get-WFListBoxItem -ListBox $ListBox1 -selectedItem
     
    .NOTES
        Author: Francois-Xavier Cat
        Twitter:@LazyWinAdm
        www.lazywinadmin.com
        github.com/lazywinadmin
#>

    
    [CmdletBinding(DefaultParameterSetName = 'All')]
    param
    (
        [Parameter(ParameterSetName = 'All')]
        [Parameter(ParameterSetName = 'Selected')]
        [ValidateNotNull()]
        [System.Windows.Forms.ListBox]$ListBox,
        
        [Parameter(ParameterSetName = 'Selected')]
        [switch]$SelectedItem,
        
        [Parameter(ParameterSetName = 'All')]
        [switch]$All
    )
    
    BEGIN
    {
        Add-Type -AssemblyName System.Windows.Forms
    }
    PROCESS
    {
        #All
        IF ($PSBoundParameters['All'])
        {
            $ListBox.Items
        }
        
        IF ($PSBoundParameters['SelectedItem'])
        {
            $ListBox.SelectedItems
        }
    }
} #Get-ListBoxItem