Question ProgressBar et WFP

$ScriptDir = Split-Path $script:MyInvocation.MyCommand.Path
[System.Reflection.Assembly]::LoadWithPartialName('System.Windows.Forms')  				| out-null
[System.Reflection.Assembly]::LoadWithPartialName('presentationframework') 				| out-null
[System.Reflection.Assembly]::LoadFrom("$ScriptDir\assembly\MahApps.Metro.dll") | out-null
[System.Reflection.Assembly]::LoadFrom("$ScriptDir\assembly\MahApps.Metro.IconPacks.dll") | out-null

[xml]$xaml = @"
<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"		
xmlns:Controls="clr-namespace:MahApps.Metro.Controls;assembly=MahApps.Metro"
xmlns:iconPacks="http://metro.mahapps.com/winfx/xaml/iconpacks" 
MaxHeight="100" MinHeight="100" Height="167" 
MaxWidth="320" MinWidth="320" Width="320" 
WindowStyle="ToolWindow">
    <Canvas Grid.Row="1" HorizontalAlignment="Left" Width="312" Height="70" VerticalAlignment="Top">
        <TextBlock Name="ProgressText" Canvas.Top="10" Canvas.Left="20">Hello world</TextBlock>
        <ProgressBar Name="Progbar" Canvas.Top="40" Canvas.Left="10" Width="260" Height="20" HorizontalAlignment="Center" Value="20" />
        <Button Content="feu" Name="bouton" Height="25" Canvas.Left="152" Canvas.Top="10" Width="118"/>
        <!-- <Controls:ProgressRing/> -->
        <Controls:ProgressRing Foreground="Red" Name = "Progring" />
    </Canvas>
</Window>
"@

function Affichage
{
PAram ( $ValueAffiche )
        $progBar.Value = $ValueAffiche
        $progBar.ValueChanged
        $progBar.IsEnabledChanged
}

function test
{
Param ( [boolean]$ValueAffich )
        $Progring.IsActive = $ValueAffich
}

$reader = New-Object System.Xml.XmlNodeReader $xaml
$dialog = [Windows.Markup.XamlReader]::Load($reader)
# Les variables d’objets graphiques
$Xaml.SelectNodes("//*[@Name]") | ForEach-Object { Set-Variable -Name "$($_.Name)" -Value $dialog.FindName($_.Name) }
# get an handle for the progress bar
#$progBar = $dialog.FindName("ProgressComplete")
$Progring.IsActive = $false

$bouton.Add_Click(
{
#    $Value = 0;
#    affichage $value
    test $true
    do
    {
        affichage $Value
        if($Value -eq 100)
        {
            #$dialog.close()
            #this.Close();
            $progBar.Name = "fini"
        }
        $Value += 0.25
        Write-Host ("value : $progBar.value")
        Start-Sleep -Seconds 0.2
    }
    While ($Value -ne 100)
test $false
})
$dialog.ShowDialog() | out-null