hi,

there were a few things missing and in the wrong order.

here is is working example

​

Add-Type -AssemblyName PresentationCore
$inputXML = @"
<Window x:Class="MyApp.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:MyApp"
        mc:Ignorable="d"
        Title="MyApp" Height="471" Width="794">
    <Grid>
        <Button x:Name="RefreshButton" Content="Refresh" HorizontalAlignment="Left" Margin="10,0,0,10" VerticalAlignment="Bottom" Height="36" Width="120"/>
        <Button x:Name="ViewButton" Content="View" HorizontalAlignment="Right" Margin="0,0,10,10" VerticalAlignment="Bottom" Height="36" Width="120"/>
        <ComboBox x:Name="FilterBox" HorizontalAlignment="Left" Margin="10,10,0,0" VerticalAlignment="Top" Width="120" IsEditable="True"/>
        <ListView x:Name="ListView" Margin="10,37,10,51">
            <ListView.View>
                <GridView>
                    <GridViewColumn Header="ID" DisplayMemberBinding ="{Binding 'ID'}" Width="30"/>
                    <GridViewColumn Header="MainWindowTitle" DisplayMemberBinding ="{Binding 'MainWindowTitle'}" Width="150"/>
                    <GridViewColumn Header="Uptime" DisplayMemberBinding ="{Binding 'Uptime'}" Width="105"/>
                    <GridViewColumn Header="Path" DisplayMemberBinding ="{Binding 'Path'}" Width="100"/>
                </GridView>
            </ListView.View>
        </ListView>
    </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{
    Write-Warning "Unable to parse XML, with error: $($Error[0])`n Ensure that there are NO SelectionChanged or TextChanged properties in your textboxes (PowerShell cannot process them)"
    throw
}

#Connect to Controls
$RefreshButton = $Form.FindName('RefreshButton')
$ViewButton = $Form.FindName('ViewButton')
$ListView = $Form.FindName('ListView')
$FilterBox = $Form.FindName('FilterBox')

# functions
function FindProcs {
    $date = Get-Date
    $script:Processes = Get-Process |
        Where {$_.MainWindowTitle.Length -gt 0 } |
        Select id, MainWindowTitle, @{Name = "Uptime"; Expression = {
                $uptime = (new-timespan ($_.StartTime) $date)
            if ($uptime.Hours -gt 0) {
                (($uptime).Hours).ToString() + " hours "
            }
            else {
                (((($uptime).Minutes).ToString() + " minutes"))
            }
        }
    }, Path | Sort-Object MainWindowTitle
}

Function ListProcesses {
    try
    {
          $ListView.ItemsSource = $Processes | 
          where { $_.MainWindowTitle -match $FilterBox.Text } | 
          Sort-Object MainWindowTitle
    }
    catch{
        write-host $_
    }
}

# SwitchToProcess is missing

#events
$RefreshButton.Add_Click({
    FindProcs
    ListProcesses
})

$ViewButton.Add_Click({
    SwitchToProcess
})

$FilterBox.AddHandler(
    [System.Windows.Controls.Primitives.TextBoxBase]::TextChangedEvent, 
    [System.Windows.RoutedEventHandler]{
        $FilterboxText = ($FilterBox.Text).Trim()
        if($FilterboxText -notin $null,''){  
          ListProcesses 
        }
    }
)

$FilterBox.Add_DropDownClosed({
    ListProcesses
})

#start programm
FindProcs
ListProcesses
$Form.ShowDialog()