public class FileStatus
{
  [DllImport("kernel32.dll")]
  private static extern IntPtr _lopen(string lpPathName, int iReadWrite);
  [DllImport("kernel32.dll")]
  private static extern bool CloseHandle(IntPtr hObject);
  private const int OF_READWRITE = 2;
  private const int OF_SHARE_DENY_NONE = 0x40;
  private static readonly IntPtr HFILE_ERROR = new IntPtr(-1);
  public static int FileIsOpen(string fileFullName)
  {
   if (!File.Exists(fileFullName))
   {
    return -1;
   }
   IntPtr handle = _lopen(fileFullName, OF_READWRITE | OF_SHARE_DENY_NONE);
   if (handle == HFILE_ERROR)
   {
    return 1;
   }
   CloseHandle(handle);
   return 0;
  }
}

class Program
{
  static void Main(string[] args)
  {
   string testFilePath = AppDomain.CurrentDomain.SetupInformation.ApplicationBase + @"testOpen.txt";
   FileStream fs = new FileStream(testFilePath, FileMode.OpenOrCreate, FileAccess.Read);
   BinaryReader br = new BinaryReader(fs);
   br.Read();
   Console.WriteLine("文件被打開");
   int result =FileStatus.FileIsOpen(testFilePath);
   Console.WriteLine(result);
   br.Close();
   Console.WriteLine("文件被關閉");
   result = FileStatus.FileIsOpen(testFilePath);
   Console.WriteLine(result);
   Console.ReadLine();
  }
}