Condition using File :: Exists not working

I am currently creating my first MSBuild-script.

I have a "Folders" tag that finds all directories in a given root path:

<?xml version="1.0" encoding="utf-8"?>
<Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003" ToolsVersion="4.0">
  <Target Name="Build">
    <PropertyGroup>
      <RootFolder>tmp</RootFolder>
    </PropertyGroup>
    <ItemGroup>
      <Folders Include="$([System.IO.Directory]::GetDirectories(&quot;$(RootFolder)&quot;))"/>
    </ItemGroup>
    <Message Text="@(Folders -> '%(FullPath)\Bin\Debug\%(Filename)%(Extension).dll', ';')"/>
  </Target>
</Project>

      

        
        
        
      

    

This works great. My problem is that I only want the directories where the specified file is listed. I tried a condition like this

Condition="$([System.IO.File]::Exists("%(FullPath)\\Bin\\Debug\\%(Filename)%(Extension).dll"))"

      

        
        
        
      

    

for the folder tag.

This script runs without error, but my list is empty. Why?

Are there any other solutions to validate the file?

I used this solution because it uses C # and I am a C # developer.

<?xml version="1.0" encoding="utf-8"?>
<Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003" ToolsVersion="4.0">
  <Target Name="Build">
    <PropertyGroup>
      <RootFolders>tmp</RootFolders>
    </PropertyGroup>
    <GetFiles rootFolders="$(RootFolders)">
      <Output PropertyName="Files" TaskParameter="Files" />
    </GetFiles>
    <Message Text="$(Files)" />
  </Target>

  <UsingTask
      TaskName="GetFiles"
      TaskFactory="CodeTaskFactory"
      AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.v4.0.dll">
      <ParameterGroup>
        <rootFolders ParameterType="System.String" Required="true" />
        <files ParameterType="System.String" Output="true" />
      </ParameterGroup>
      <Task>
          <Using Namespace="System" />
          <Using Namespace="System.IO" />
          <Using Namespace="System.Linq" />
          <Code Type="Fragment" Language="cs">
              <![CDATA[               
                  Func<string, string> BuildFilePath = path => path + @"\Bin\Debug\" + Path.GetFileName(path) + ".dll";
                  var dirs = Directory.GetDirectories(rootFolders).Where(x => File.Exists(BuildFilePath(x)));
                  files = string.Join("\n", dirs.Select(BuildFilePath));
              ]]>
          </Code>
      </Task>
  </UsingTask>
</Project>