xml - How to add Propertygroup of csproj? -

we doing delay sign of our csproject. opening each csproject file doing time consuming task decided write powershell script.

function new-xmlnode {     [cmdletbinding()]     [outputtype([string])]     param     (         # webconfig file full path         [parameter(mandatory=$true,                    valuefrompipelinebypropertyname=$true,                    position=0)]         [string]$path,         [string] $xpath,                       [string] $node,                       [string] $logfile = "$env:temp\newxmlnode.log"     )          try          {                         if (-not (test-path -path $path))              {                    throw [system.io.filenotfoundexception] "$path not found."             }             else              {                  $xml = new-object -typename xml                 $xml.load($path)                                              # getting values                 $items  = select-xml -xml $xml -xpath $xpath                 if ( $items -ne $null) # if xpath valid                  {                     foreach ($item in $items)                      {                             [system.xml.xmldocumentfragment] $newnode = $xml.createdocumentfragment()                         $newnode.innerxml = $node                         $item.node.appendchild($newnode)                     }                  }                 else # if xpath not valid log error                  {                     write "$(get-date -format $datetimeformat) ## error ## $($myinvocation.mycommand.name) ## given xpath $xpath xml $path not valid" | out-file $logfile -append                 }                 $xml.save($path)             }         }         catch          {              write $_.exception.errorrecord | out-file -filepath $logfile -append             throw "$(get-date -format $datetimeformat) ## error ## $($myinvocation.mycommand.name) ## $_ "         } }  function set-strongnamesign {     param     (         $path="m:\myproject\myproject.csproj"     )          $ns = @{ dns = "http://schemas.microsoft.com/developer/msbuild/2003" }      new-xmlnode -path $path -xpath "/$ns:project" -node '<propertygroup>     <signassembly>true</signassembly>     </propertygroup>' }  set-strongnamesign 

when running getting following error.

## error ## new-xmlnode ## exception calling "appendchild" "1" argument(s): "this document has 'documentelement' node." @ line:51 char:13 +             throw "$(get-date -format $datetimeformat) ## error ## $($myinvocati ... + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~     + categoryinfo          : operationstopped: (02/26/2016 11:1...lement' node." :string) [], runtimeexception     + fullyqualifiederrorid : 02/26/2016 11:17:33 ## error ## new-xmlnode ## exception calling "appendchild" "1" argument(s): "this document has 'documentelement' node."

how solve this? need add few more propertygroup , 1 itemgroup too.

try add namespace-prefix mapping parameter of function, $namespaces, , use registered prefix in xpath :

function new-xmlnode {     .....     # getting values     $items  = select-xml -xml $xml -xpath $xpath -namespace $namespaces     ...... }  function set-strongnamesign {     param     (         $path="m:\myproject\myproject.csproj"     )      $ns = @{ dns = "http://schemas.microsoft.com/developer/msbuild/2003" }      # use registered prefix `dns` in xpath , pass mapping parameter :     new-xmlnode -path $path -xpath "/dns:project" -namespaces $ns -node '<propertygroup>     <signassembly>true</signassembly>     </propertygroup>' }