Check this MSDN that will resolve your query.
The .sln file contains text-based information the environment uses to
find and load the name-value parameters for the persisted data and the
project VSPackages it references. When a user opens a solution, the
environment cycles through the preSolution, Project, and postSolution
information in the .sln file to load the solution, projects within the
solution, and any persisted information attached to the solution.
Also check EnvDTE : Getting all projects .
Also check this Thread(Full credit to John Leidegren for providing such a nice answer)
public class Solution
{
//internal class SolutionParser
//Name: Microsoft.Build.Construction.SolutionParser
//Assembly: Microsoft.Build, Version=4.0.0.0
static readonly Type s_SolutionParser;
static readonly PropertyInfo s_SolutionParser_solutionReader;
static readonly MethodInfo s_SolutionParser_parseSolution;
static readonly PropertyInfo s_SolutionParser_projects;
static Solution()
{
s_SolutionParser = Type.GetType("Microsoft.Build.Construction.SolutionParser, Microsoft.Build, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a", false, false);
if (s_SolutionParser != null)
{
s_SolutionParser_solutionReader = s_SolutionParser.GetProperty("SolutionReader", BindingFlags.NonPublic | BindingFlags.Instance);
s_SolutionParser_projects = s_SolutionParser.GetProperty("Projects", BindingFlags.NonPublic | BindingFlags.Instance);
s_SolutionParser_parseSolution = s_SolutionParser.GetMethod("ParseSolution", BindingFlags.NonPublic | BindingFlags.Instance);
}
}
public List<SolutionProject> Projects { get; private set; }
public Solution(string solutionFileName)
{
if (s_SolutionParser == null)
{
throw new InvalidOperationException("Can not find type 'Microsoft.Build.Construction.SolutionParser' are you missing a assembly reference to 'Microsoft.Build.dll'?");
}
var solutionParser = s_SolutionParser.GetConstructors(BindingFlags.Instance | BindingFlags.NonPublic).First().Invoke(null);
using (var streamReader = new StreamReader(solutionFileName))
{
s_SolutionParser_solutionReader.SetValue(solutionParser, streamReader, null);
s_SolutionParser_parseSolution.Invoke(solutionParser, null);
}
var projects = new List<SolutionProject>();
var array = (Array)s_SolutionParser_projects.GetValue(solutionParser, null);
for (int i = 0; i < array.Length; i++)
{
projects.Add(new SolutionProject(array.GetValue(i)));
}
this.Projects = projects;
}
}
[DebuggerDisplay("{ProjectName}, {RelativePath}, {ProjectGuid}")]
public class SolutionProject
{
static readonly Type s_ProjectInSolution;
static readonly PropertyInfo s_ProjectInSolution_ProjectName;
static readonly PropertyInfo s_ProjectInSolution_RelativePath;
static readonly PropertyInfo s_ProjectInSolution_ProjectGuid;
static SolutionProject()
{
s_ProjectInSolution = Type.GetType("Microsoft.Build.Construction.ProjectInSolution, Microsoft.Build, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a", false, false);
if (s_ProjectInSolution != null)
{
s_ProjectInSolution_ProjectName = s_ProjectInSolution.GetProperty("ProjectName", BindingFlags.NonPublic | BindingFlags.Instance);
s_ProjectInSolution_RelativePath = s_ProjectInSolution.GetProperty("RelativePath", BindingFlags.NonPublic | BindingFlags.Instance);
s_ProjectInSolution_ProjectGuid = s_ProjectInSolution.GetProperty("ProjectGuid", BindingFlags.NonPublic | BindingFlags.Instance);
}
}
public string ProjectName { get; private set; }
public string RelativePath { get; private set; }
public string ProjectGuid { get; private set; }
public SolutionProject(object solutionProject)
{
this.ProjectName = s_ProjectInSolution_ProjectName.GetValue(solutionProject, null) as string;
this.RelativePath = s_ProjectInSolution_RelativePath.GetValue(solutionProject, null) as string;
this.ProjectGuid = s_ProjectInSolution_ProjectGuid.GetValue(solutionProject, null) as string;
}
}