retrieve-projects-from-sln-in-MSBUILD

 <UsingTask TaskName="GetProjectsFromSolutionCodeTask" TaskFactory="CodeTaskFactory" AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll">
    <ParameterGroup>
      <Solution ParameterType="System.String" Required="true" />
      <Output ParameterType="Microsoft.Build.Framework.ITaskItem[]" Output="true" />
      
    </ParameterGroup>
    <Task>
      <Reference Include="System.Xml" />
      <Reference Include="Microsoft.Build" />
      <Using Namespace="Microsoft.Build.Construction" />
      <Code Type="Fragment" Language="cs"><![CDATA[
        var _solutionFile = SolutionFile.Parse(Solution); 
        Output = _solutionFile.ProjectsInOrder
            .Where(proj => proj.ProjectType == SolutionProjectType.KnownToBeMSBuildFormat)
            .Select(proj => new TaskItem(proj.AbsolutePath))
            .ToArray();
      ]]></Code>
    </Task>
  </UsingTask>
  <Target Name="BeforeBuild" >
    <GetProjectsFromSolutionCodeTask Solution="$(SolutionPath)">
      <Output ItemName="ProjectFiles" TaskParameter="Output" />
    </GetProjectsFromSolutionCodeTask>
    <!-- This message wont be shown until you change settings under 'Buid & run' from minmal  -->
    <Message Condition="true" Importance="High" text="Testing: @(ProjectFiles)">
    </Message>
  </Target>