How do I use Powershell to add/remove references to a csproj?

Question

In relation to this previous question I am trying to create a batch file which as part must remove and add a reference to an XML *.csproj file. I have looked at this, this, this and this previous question but as a powershell n00b am unable to get it working (so far).

Can anyone help me with the following? I want to remove two specific references in a VS2010 csproj file (XML) and add a new reference.

I opened the csproj and the reference can be found at the following location

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">

  <!--          ...         -->
  <!-- Omitted for brevity  -->
  <!--          ...         -->

  <ItemGroup Condition="'$(BuildingInsideVisualStudio)' == 'true'">
    <AvailableItemName Include="Effect" />
  </ItemGroup>
  <ItemGroup>
    <ProjectReference Include="..\SomeDirectory\SomeProjectFile.csproj">
      <Project>{AAB784E4-F8C6-4324-ABC0-6E9E0F73E575}</Project>
      <Name>SomeProject</Name>
    </ProjectReference>
    <ProjectReference Include="..\AnotherDirectory\AnotherProjectFile.csproj">
      <Project>{B0AA6A94-6784-4221-81F0-244A68C374C0}</Project>
      <Name>AnotherProject</Name>
    </ProjectReference>
  </ItemGroup>

  <!--          ...         -->
  <!-- Omitted for brevity  -->
  <!--          ...         -->

</Project>

Basically I want to:

• remove these two references
• insert a new reference to a pre-compiled DLL specified by relative path
• OR Add an Assembly Reference Location to the project specified by relative path

As a very simple example I have tried the following powershell script to delete all the ProjectReference nodes. I pass the path to csproj as argument. I get the error Cannot validate the argument 'XML'. The Argument is null or empty. I can confirm it is loading the csproj and saving it in-place unmodified so the path is correct.

param($path)
$MsbNS = @{msb = 'http://schemas.microsoft.com/developer/msbuild/2003'}

function RemoveElement([xml]$Project, [string]$XPath, [switch]$SingleNode)
{
    $xml | Select-Xml -XPath $XPath | ForEach-Object{$_.Node.ParentNode.RemoveAll()}
}

$proj = [xml](Get-Content $path)
[System.Console]::WriteLine("Loaded project {0} into {1}", $path, $proj)

RemoveElement $proj "//ProjectReference" -SingleNode

    # Also tried
    # RemoveElement $proj "/Project/ItemGroup/ProjectReference[@Include=`'..\SomeDirectory\SomeProjectFile.csproj`']" -SingleNode
    # but complains cannot find XPath

$proj.Save($path)

What am I doing wrong? Any comments/suggestions welcome :)

Answer 1

I think the problem is that your XML file has a default namespace xmlns="http://schemas.microsoft.com/developer/msbuild/2003". This causes problems with XPath. So you XPath //ProjectReference will return 0 nodes. There are two ways to solve this:

1. Use a namespace manager.
2. Use namespace agnostic XPath.

Here's is how you could use a namespace manager:

$nsmgr = New-Object System.Xml.XmlNamespaceManager -ArgumentList $proj.NameTable
$nsmgr.AddNamespace('a','http://schemas.microsoft.com/developer/msbuild/2003')
$nodes = $proj.SelectNodes('//a:ProjectReference', $nsmgr)

Or:

Select-Xml '//a:ProjectReference' -Namespace $nsmgr

Here's how to do it using namespace agnostic XPath:

$nodes = $proj.SelectNodes('//*[local-name()="ProjectReference"]')

Or:

$nodes = Select-Xml '//*[local-name()="ProjectReference"]'

The second approach can be dangerous because if there were more than one namespace it could select the wrong nodes but not it your case.