PowerShell: Collection was modified; enumeration operation may not execute

 

While the following example is for PowerShell, the same applies to C# code.

Collections that are being modified do not like to be processed with FOR EACH.
"Collection was modified; enumeration operation may not execute"

For example:

$web = Get-SPWeb someurl...

ForEach($list in $w.Lists)
{
  if (!$list.Hidden)
  {
    # do something to change the list
    # like add a new view...

    $list.Views.Add(.......)
    # error! 
    # "Collection was modified; enumeration operation may not execute..."
  }
 }
$web.Dispose()

 

The Fix

Change the FOR EACH to a FOR.

change:

  foreach($l in $web.Lists)
     {

to:

   for ($i=0; $i -lt $web.lists.count; $i++)
     {
        $l = $w.lists[$i]

 

And if you are deleting items in the collection…

Walk the collection in reverse order!

   for ($i=$web.lists.count-1; $i –gt 0; $i--)
     {
        $l = $web.lists[$i]

.