I was just having some fun with some recent blog posts…

WPF & PowerShell – Part 5 has a script for “Get-Listbox” and for “Show-Control” and Halr9000 wrote a script he called Get-PSBlogroll

I had modified the example from the WPF post to create a listbox which will “start” whatever you double click …


Get-Listbox Title | Show-Control @{
   "MouseDoubleClick" = { [Diagnostics.Process]::Start( $window.Content.SelectedItem ) }
}
 

And I tried something like this to let me launch links from hal9000’s blogroll:


Get-PsBlogRoll | % { $_.HtmlUrl } | Get-Listbox | Show-Control @{
   "MouseDoubleClick" = { [Diagnostics.Process]::Start( $window.Content.SelectedItem ) }
}
 

Of course, what I’d like is to see the titles, instead of the URL, but because of how Get-ListBox was written, it only accepts strings, and therefore only returns strings. I tried adding the URL as a NoteProperty on the title string, but there’s a bug in the script cmdlet implementation that strips ETS properties. So if you specify your parameter type as a [string], you loose the NoteProperty.

Idea 1: Use [PsObject] for your pipeline parameter

Of course, if they fix the bug this tip will go away, but in the meantime, you’re better off not casting the input from the PowerShell native [PsObject] type, because you loose any extended type system attributes (and if you cast XML to a string, it comes out yucky).

Idea 2: Don’t output xml nodes

Even after fixing the Get-Listbox script so it outputs what it gets in without casting it, I still have to craft PsObjects with the output from Halr9000’s script, because otherwise Get-ListBox just outputs the .ToString() representation of the xml node, which is invariably useless — I could data-bind to the xml attributes, but it requires a separate syntax in the XAML — which means you’d have to have separate code for xml vs objects. So basically, you’re better off with a | Select * at the end of your Get-PsBlogRoll.

Idea 3: Display scripts should take a property (or a property list)...

What I eventually ended up doing is rewriting Get-Listbox to take a “Properties” parameter so that I could specify which of the attributes of an object I wanted to use … that way, I can pass in the almost unmodified output from Get-PSBlogRoll into the new Get-ListBox, and run with it. In the end, it looks something like this:


cmdlet Get-Listbox {
   param(   
    [Parameter(ValueFromPipeline=$true, Mandatory=$true)]$Input,
    [Parameter(Position=0,Mandatory=$false)][string[]]$Properties
    )
   Begin{
      $listItems = @()       
   }
   Process
   {
      if( $input -is [type] -and $input.IsEnum )
      {
         $listItems+= [Enum]::GetValues($input)
      }
      elseif( $input.GetType().IsEnum )
      {
         $listItems+= [Enum]::GetValues($input.GetType())           
      }
      else
      {
         $listItems += $input
      }               
   }
   
   End
   {
      $listbox = New-Object System.Windows.Controls.Listbox
      $listBox.ItemsSource = $listItems # | Select -unique

      # An optional DataTemplate, if they specified which properties they want to see
      if($Properties) {
         $xml = "<DataTemplate xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation'><StackPanel>"
         foreach($property in $Properties) {
            $xml += "<TextBlock Text='{Binding Path=$($property)}'/>"
         }
         [XML]$xml = $xml + "</StackPanel></DataTemplate>"
         
         $listBox.ItemTemplate = [Windows.Markup.XamlReader]::Load(
            (New-Object System.Xml.XmlNodeReader $xml))
      }
     
      $listBox
    }
}

function Get-PsBlogRoll {
   $webClient = new-object System.Net.WebClient
   [xml]$Opml = $webClient.DownloadString("http://bloglines.com/export?id=halr9000")
   $PsBlogroll = $Opml.opml.body.outline | Where-Object { $_.text -eq '@Powershell' }
   ## The Select statement outputs a custom PSObject instead of the original (XmlNode) object
   $PsBlogroll.Outline | Select-Object title, text, htmlUrl, xmlUrl
}

Get-PSBlogRoll | Get-Listbox title | Show-Control @{
   "MouseDoubleClick" = {
      # But now I can use the "HtmlUrl" property to launch it in my browser
      [Diagnostics.Process]::Start( $window.Content.SelectedItem.HtmlUrl )
   }
}
 

Of course, because of how I wrote the DataTemplate for the properties (using a StackPanel and a loop to output multiple TextBlock objects) you could choose to show the Url as well, and all you’d have to do is change the call to Get-Listbox like this: Get-Listbox title,htmlUrl … which is pretty cool. Does anyone else have any ideas for making these even easier to compose?

A really nice trick would be if the wpf cmdlet could use Write-Output in the click handler and actually yield to allow the rest of the pipeline to process that item, but so far, I haven’t been able to find a way to do that (short of closing the WPF window, of course).