C# 实现在当前目录基础上找到上一层目录

/// <summary>
    /// 获得项目的根路径
    /// </summary>
    /// <returns></returns>
    public string GetProjectRootPath()
    {
      string rootPath = "";
      string BaseDirectoryPath = AppDomain.CurrentDomain.BaseDirectory; // F:\project\WPF\AstroATE-PDR\04. 程序\01. 源代码\AstroATE\AstroATE\bin\Debug
      // 向上回退三级，得到需要的目录
      rootPath = BaseDirectoryPath.Substring(0, BaseDirectoryPath.LastIndexOf("\\")); // 第一个\是转义符，所以要写两个
      rootPath = rootPath.Substring(0, rootPath.LastIndexOf(@"\"));  // 或者写成这种格式
      rootPath = rootPath.Substring(0, rootPath.LastIndexOf("\\")); // @"F:\project\WPF\AstroATE-PDR\04. 程序\01. 源代码\AstroATE\AstroATE
      return rootPath;
    }

string str = GetProjectRootPath() + @"\data\帮助文档.pdf";  //找到需要找的文件

DirectoryInfo di = new DirectoryInfo(string.Format(@"{0}..\..\", Application.StartupPath)); 
di.FullName

DirectoryInfo info = new DirectoryInfo(Application.StartupPath); 
String path = info.Parent.Parent.FullName;

string WantedPath = Application.StartupPath.Substring(0,Application.StartupPath.LastIndexOf(@"\"));