asp net problem, searching in a file

<pre lang="cs">public string GetImagePath(string id)
      {
          const string f2 = "C:\\idimg.txt";
          string myline;
          using (StreamReader r = new StreamReader(f2))
          {
              // 3
              // Use while != null pattern for loop


              while ((myline = r.ReadLine()) != null)
              {

                  string[] attr = myline.Split('|');
                  string myidimage = attr[0].ToString().Trim();
                  string pathimage = attr[1];
                  if (id == myidimage)
                  {
                      myline = pathimage;
                      return myline;
                  }
                  return null;

              }
          }