Check the MSDN that will resolve your request.
The .sln file contains textual information used by the environment to find and load name parameters for the stored data, and the VSPackages project is the link. When the user opens the solution, the environment loops through the preSolution, Project and postSolution information in the .sln file to load the solution, projects within the solution and any permanent information that is attached to the solution.
Also check out EnvDTE: getting all projects .
Also check out this Thread ( John Leidegren Full Credit for such a good 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; } }