How do you update a WPF form during code execution

I am using the code below to write a script that calls a WPF form. i would like to have the form being updated during code execution but whatever i try the code keeps running and only update the form afther execution. 

so basically i need to run code:

update the forum with these settings and than start the following code.

anybody have an idea?

  Add-Type-AssemblyNamePresentationCore,PresentationFramework,WindowsBase,system.windows.forms

    #load validation form

    [xml]$Global:xmlval=Get-Content-Path"$localdeploypath\scripts\dagform\validationform.xaml"

    #correct source path for images

    $xmlval.window.innerXml =$xmlval.window.innerXml.Replace('Source="','Source="'+$localdeploypath+'\scripts\dagform\')

    #Create the XAML reader using a new XML node reader

    $Global:xamvalGUI=[Windows.Markup.XamlReader]::Load((new-objectSystem.Xml.XmlNodeReader$xmlval))

    #Create hooks to each named object in the XAML

    $xmlval.SelectNodes("//*[@Name]") |%{

     Set-Variable-Name ($_.Name) -Value$xamvalGUI.FindName($_.Name) -ScopeGlobal

    }

    #endregion load validation form

    #region Buttons

    $createdag.add_Click({

        $xamvalGUI.close()

    })

    #endregion Buttons

    #region events

    $xamvalGUI.add_Loaded({

    $errorbox2.Visibility ="visible"

    $errorbox2.text ="start"

    $global:xamvalGUI.Updatelayout()

    start-sleep-seconds10

    $errorbox2.text ="mid"

    $global:xamvalGUI.Updatelayout()

    start-sleep-seconds10

    $errorbox2.text ="end"

    })

    $xamvalGUI.add_sourceinitialized({

    #create timer object

        $Global:timer=new-objectSystem.Windows.Threading.DispatcherTimer

        $timer.interval =[timespan]"0:0:0.1"

        #add event per tick

        $timer.add_tick({

           $global:xamvalGUI.Updatelayout()

            write-host"form updated"

        })

        #start timer

        $timer.start()

    })

    #endregion events

  $xamvalGUI.ShowDialog()

    $errorbox2.Visibility ="visible"

    $errorbox2.text ="start"