在 asp.net 中，viewstate 因為在客戶端的 html 里占據大量的空間，并隨著頁面的 postback 反復傳遞于網絡中，一直為人垢病。但是實際上 viewstate 可以存儲到數據庫、緩存等任意地方，從而避免頻繁將冗長的 base64 字符串發送到客戶端。這樣做不但可以顯著提高性能（大幅度減少了網絡傳輸的字節數），而且如果其中的內容也不會被輕易解密和破解。因此這個方法是很有用處的。
以下寫了一個簡單的例子，用緩存來作為 viewstate 存儲目的地。至于緩存的 key，文中給出的只是一個簡單的寫法，具體可以根據情況給出嚴密的方案。
代碼大致演示如下：
<%@ page language="c#" codebehind="saveviewstatetoother.aspx.cs" autoeventwireup="false" inherits="linkedlist.saveviewstatetoother" %>
<!doctype html public "-//w3c//dtd html 4.0 transitional//en" >
<html>
<head>
<title>saveviewstatetoother</title>
<meta name="generator" content="microsoft visual studio .net 7.1">
<meta name="code_language" content="c#">
<meta name=vs_defaultclientscript content="javascript">
<meta name=vs_targetschema content="http://schemas.microsoft.com/intellisense/ie5">
</head>
<body ms_positioning="gridlayout">
<form id="form1" method="post" runat="server"><asp:datagrid id=datagrid1 runat="server" bordercolor="#3366cc" borderstyle="none" borderwidth="1px" backcolor="white" cellpadding="4" pagesize="6" allowpaging="true">
<selecteditemstyle font-bold="true" forecolor="#ccff99" backcolor="#009999">
</selecteditemstyle>
<itemstyle forecolor="#003399" backcolor="white">
</itemstyle>
<headerstyle font-bold="true" forecolor="#ccccff" backcolor="#003399">
</headerstyle>
<footerstyle forecolor="#003399" backcolor="#99cccc">
</footerstyle>
<pagerstyle horizontalalign="left" forecolor="#003399" backcolor="#99cccc" pagebuttoncount="20" mode="numericpages">
</pagerstyle>
</asp:datagrid>
</form>
</body>
</html>
using system;
using system.data;
using system.io;
using system.text;
using system.web.ui;
using system.web.ui.webcontrols;
namespace linkedlist
{
/// <summary>
/// saveviewstatetoother 的摘要說明。
/// </summary>
public class saveviewstatetoother : page
{
protected datagrid datagrid1;
private void page_load(object sender, eventargs e)
{
if (!ispostback)
bind();
}
private void bind()
{
datatable table = new datatable();
table.columns.add("id", typeof (int));
table.columns.add("name", typeof (string));
for (int i = 0; i < 1000; i++)
{
datarow row = table.newrow();
row["id"] = i;
row["name"] = "student_" + i.tostring();
table.rows.add(row);
}
datagrid1.datasource = table;
datagrid1.databind();
}
#region web 窗體設計器生成的代碼
protected override void oninit(eventargs e)
{
initializecomponent();
base.oninit(e);
}
private void initializecomponent()
{
this.datagrid1.pageindexchanged += new system.web.ui.webcontrols.datagridpagechangedeventhandler(this.datagrid1_pageindexchanged);
this.load += new system.eventhandler(this.page_load);
}
#endregion
protected override void savepagestatetopersistencemedium(object viewstate)
{
losformatter format = new losformatter();
stringwriter writer = new stringwriter();
format.serialize(writer, viewstate);
string vsraw = writer.tostring();
byte[] buffer = convert.frombase64string(vsraw);
string vstext = encoding.ascii.getstring(buffer);
object v = cache[pagekey];
if (v == null)
cache.insert(pagekey, vstext);
else
cache[pagekey] = vstext;
}
public string pagekey
{
get { return session.sessionid + "_page_saveviewstatetoother_aspx"; }
}
protected override object loadpagestatefrompersistencemedium()
{
object s = cache[pagekey];
if (s != null)
{
string state = s.tostring();
byte[] buffer = encoding.ascii.getbytes(state);
string vsraw = convert.tobase64string(buffer);
losformatter formatter = new losformatter();
return formatter.deserialize(vsraw);
}
return null;
}
private void datagrid1_pageindexchanged(object source, datagridpagechangedeventargs e)
{
datagrid1.currentpageindex = e.newpageindex;
bind();
}
}
}
對于實際的應用，如果要決定在整個程序中應用此方案，則使用一個通用的頁面基類，在其中實現此機制比較合適。
出處：木野狐 blog
新聞熱點
疑難解答
圖片精選
