powershit/test/Get-Listbox.ps1

function Get-Listbox() {

cmdlet `
  -DefaultParameterSet Type `
  
    param(   
    [Parameter(ParameterSetName="Type", ValueFromPipeline=$true, Mandatory=$true)]
    [Type]
    $type,

    [Parameter(ParameterSetName="Enum", ValueFromPipeline=$true, Mandatory=$true)]
    [Enum]
    $enum,

    [Parameter(ParameterSetName="String", ValueFromPipeline=$true, Mandatory=$true)]
    [string]
    $string
    )

   Begin{
       $listItems = @()       
   }
   Process
   {
       switch ($psCmdlet.ParameterSetName) {
         "Type" {
           if ($type.IsEnum) {
               $listItems+= [Enum]::GetValues($type)
           }
         }
         "Enum" {
           $listItems+= [Enum]::GetValues($enum.GetType())           
         }
         "String" { $listItems += $string } 
       }               
   }
    
   End
   {
       $listbox = New-Object Windows.Controls.Listbox
       $listBox.ItemsSource = $listItems | Select -unique
       $listBox
    }
}