#PUT XAML BELOW between the @" "@ 
$inputXML = @"
<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApplication1"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        
    </Grid>
</Window>
"@
 
$inputXML = $inputXML -replace 'mc:Ignorable="d"','' -replace "x:N",'N' -replace '^<Win.*', '<Window'
[void][System.Reflection.Assembly]::LoadWithPartialName('presentationframework')
[xml]$XAML = $inputXML

#Read XAML
 
$reader=(New-Object System.Xml.XmlNodeReader $xaml) 
try{
	$Form=[Windows.Markup.XamlReader]::Load( $reader )
}catch [System.Management.Automation.MethodInvocationException] {
	Write-Warning "We ran into a problem with the XAML code.  Check the syntax for this control..."
	write-host $error[0].Exception.Message -ForegroundColor Red
	if ($error[0].Exception.Message -like "*button*"){
		write-warning "Ensure your &lt;button in the `$inputXML does NOT have a Click=ButtonClick property.  PS can't handle this`n`n`n`n"
	}
}catch{
	Write-Host "Unable to load Windows.Markup.XamlReader. Double-check syntax and ensure .net is installed."
}
 
#===========================================================================
# Store Form Objects In PowerShell
#===========================================================================
 
$xaml.SelectNodes("//*[@Name]") | %{Set-Variable -Name "WPF$($_.Name)" -Value $Form.FindName($_.Name)}
 
Function Get-FormVariables{
if ($global:ReadmeDisplay -ne $true){Write-host "If you need to reference this display again, run Get-FormVariables" -ForegroundColor Yellow;$global:ReadmeDisplay=$true}
write-host "Found the following interactable elements from our form" -ForegroundColor Cyan
get-variable WPF*
}
 
Get-FormVariables
 
#===========================================================================
# Use this space to add code to the various form elements in your GUI
#===========================================================================
                                                                    
     
#Reference 
 
#Adding items to a dropdown/combo box
    #$vmpicklistView.items.Add([pscustomobject]@{'VMName'=($_).Name;Status=$_.Status;Other="Yes"})
     
#Setting the text of a text box to the current PC name    
    #$WPFtextBox.Text = $env:COMPUTERNAME
     
#Adding code to a button, so that when clicked, it pings a system
# $WPFbutton.Add_Click({ Test-connection -count 1 -ComputerName $WPFtextBox.Text
# })
#===========================================================================
# Shows the form
#===========================================================================
write-host "To show the form, run the following" -ForegroundColor Cyan
'$Form.ShowDialog() | out-null'

Source