private static void TestWrite()
{
   // Must specify FileOptions.Asynchronous otherwise the BeginXxx/EndXxx methods are
   // handled synchronously.
   FileStream fs = new FileStream(Program.FilePath, FileMode.OpenOrCreate,
      FileAccess.Write, FileShare.None, 8, FileOptions.Asynchronous);

   string content = "A quick brown fox jumps over the lazy dog";
   byte[] data = Encoding.Unicode.GetBytes(content);

   // Begins to write content to the file stream.
   Console.WriteLine("Begin to write");
   fs.BeginWrite(data, 0, data.Length, Program.OnWriteCompleted, fs);
   Console.WriteLine("Write queued");
}

private static void OnWriteCompleted(IAsyncResult asyncResult)
{
   // End the async operation.
   FileStream fs = (FileStream)asyncResult.AsyncState;
   fs.EndWrite(asyncResult);

   // Close the file stream.
   fs.Close();
   Console.WriteLine("Write completed");

   // Test async read bytes from the file stream.
   Program.TestRead();
}