将页面的ViewState放在Session

重写Page类中的LoadPageStateFromPersistenceMedium()和SavePageStateToPersistenceMedium(object state)方法。
Demo：将ViewState存放到Session中：
protected LosFormatter losFormatter;
protected override object LoadPageStateFromPersistenceMedium()
{
  string key = Request.RawUrl + "__viewstate";
  if (Session[key] != null)
  {
  MemoryStream stream = (MemoryStream)Session[key];
  stream.Seek(0, SeekOrigin.Begin);
  return losFormatter.Deserialize(stream);
  }
  return null;
}
protected override void SavePageStateToPersistenceMedium(object state)
{
  string key = Request.RawUrl + "__viewstate";
  MemoryStream stream = new MemoryStream();
  losFormatter.Serialize(stream, state);
  stream.Flush();
  Session[key] = stream;
}