add an item to arraylist in powershell workflow foreach -parallel

Question

How can we add an item to an arraylist while using foreach -parallel loop in powershell workflows?

workflow foreachpsptest { 
  param([string[]]$list)
  $newList = [System.Collections.ArrayList]@()
  foreach –parallel ($item in $list){
    $num = Get-Random 
    InlineScript {
      ($USING:newList).add("$num---$item")
    }
  }
  Write-Output -InputObject "randomly created new List: $newList"
} 
$list = @("asd","zxc","qwe","cnsn")
foreachpsptest -list $list

Answer 1

The problem here is that you're using, uh $using: the wrong way.

Your workflow is basically it's own sandbox. You can use $using to instantiate a variable with the same values within it, but you can't use that to manipulate the same variable outside of it.

However, you can have your workflow emit an object, and then capture that with the .Add() method of your $newlist Arraylist variable.

Tweak the code like so, and it should work:

#Moved the Arraylist declaration outside
$newList = [System.Collections.ArrayList]@()

workflow foreachpsptest { 
param([string[]]$list)
foreach –parallel ($item in $list){
      $num = Get-Random 
      InlineScript {
      #use the using: context to pass along values, then emit the current object
      "$using:num---$using:item"
      }
}
} 

$list = @("asd","zxc","qwe","cnsn")
#kick off the workflow and capture results in our arraylist
$newList.add((foreachpsptest -list $list))

Then, after the code has run, we can get the values out, like so.

$newList
58665978---qwe
173370163---zxc
1332423298---cnsn
533382950---asd

Answer 2

I don't think you can do that. This article on Powershell workflow restrictions calls out "Method Invocation on Objects" as an unsupported activity, so the .add() method on your arraylist isn't going to work.