Proprietà StateBag.Count

private string GetMruList(string selectedValue) {
   StateBag state = ViewState;
   if (state.Count > 0) {
      int upperBound = state.Count;
      string[] keys = new string[upperBound];
      StateItem[] values = new StateItem[upperBound];
      state.Keys.CopyTo(keys, 0);
      state.Values.CopyTo(values, 0);
      StringBuilder options = new StringBuilder();
      for(int i = 0; i < upperBound; i++) {
         options.AppendFormat("<option {0} value={1}>{2}", (selectedValue == keys[i])?"selected":"", keys[i], values[i].Value);
      }
      return options.ToString();
   }
   return "";
}