。net新手问题

  using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Collections.Generic;

public partial class test : System.Web.UI.Page{

  Hashtable ht;

  protected void Page_Load(object sender, EventArgs e){
  if (!Page.IsPostBack){
  ht = new Hashtable();
  ViewState["ht"] = ht;
  }

  }
   
  protected void Button_Click(object sender, EventArgs e){
  ht= (Hashtable)ViewState["ht"];
  foreach (ListItem i in ListBox1.Items) {
  if (i.Selected == true){
  ListBox2.Items.Add(i.Text);
  ht.Add(i.Text.ToString(), i.Value.ToString());
  } 
  }

  int[] indexToDel = ListBox1.GetSelectedIndices(); //取得所有选取值的index集合
  int cnt = indexToDel.Length;
  for (int i = cnt - 1; i >= 0; i--) {
  ListBox1.Items.RemoveAt(indexToDel[i]);

  }
}
  protected void Button2_Click(object sender, EventArgs e){

  ht = (Hashtable)ViewState["ht"];
  int[] indexToDel = ListBox2.GetSelectedIndices(); //取得所有选取值的index集合
  int cnt = indexToDel.Length;
  foreach(ListItem i in ListBox2.Items){
  if (i.Selected == true) {
  ht.Remove(i.Text.ToString());}
  }

  for (int i = cnt - 1; i >= 0; i--){
  ListBox2.Items.RemoveAt(indexToDel[i]);
  }
  }

  protected void Button3_Click(object sender, EventArgs e){
  ht = (Hashtable)ViewState["ht"];
  Application["ht"] = ht;
   

  Response.Redirect("right_top.aspx");
  Response.Write("<script language=javascript>") ;
  Response.Write("window.returnValue='false';window.close()") ;
  Response.Write("</script>");
  // Response.Write(" <script language=javascript>window.open('right_top.aspx');window.returnValue='True';window.close();</script>"); 

   
  }

}
当我不把ht放在ViewState["ht"] 中，当我点击每个按钮时为什么ht又实例化一次？如果不用ViewState怎么解决？请高手帮我解决一下，为什么会出现这个问题？我是新手有点迷茫

------解决方案--------------------
定义一个全局变量接收啊