ASP.NET Tutorial/Page Lifecycle/ViewState

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Convert.FromBase64String and view state encoding

   <source lang="csharp">

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="SimpleViewState" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" > <head runat="server"> 

   <title>Untitled Page</title>

</head> <body> 

   <form id="form1" runat="server">

       <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
<asp:Button ID="Button1" OnClick="Button1_Click" runat="server" Text="Button" />
   </form>

</body> </html> File: Default.aspx.cs 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; public partial class SimpleViewState : System.Web.UI.Page { 

   protected void Page_Load(object sender, EventArgs e)
   {
   Label1.Text = "Hello World!";
   }
 protected void Button1_Click(object sender, EventArgs e)
 {
   string viewStateString = "/wEPDwUKLTE2MjY5MTY1NQ9kFgICAw9kFgICAQ8PFgIeBFRleHQFDEhlbGxvIFdvcmxkIWRkZPsbiNOyNAufEt7OvNIbVYcGWHqf";
   
   byte[] stringBytes = Convert.FromBase64String(viewStateString);
   
   string decodedViewState = System.Text.Encoding.ASCII.GetString(stringBytes);
   Label1.Text = decodedViewState;
 }

}</source>


Save string variable to ViewState

   <source lang="csharp">

File: Default.aspx <%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="PreserveMembers" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" > <head runat="server"> 

   <title>Untitled Page</title>

</head> <body> 

   <form id="form1" runat="server">

       <asp:TextBox ID="txtValue" 
                    runat="server" 
                    Height="160px" 
                    TextMode="MultiLine" 
                    Width="460px">This is a test</asp:TextBox>

       

       <asp:Button ID="cmdSave" 
                   runat="server" 
                   OnClick="cmdSave_Click" 
                   Text="Save Contents" />
       <asp:Button ID="cmdLoad" 
                   runat="server" 
                   OnClick="cmdLoad_Click"
Text="Load Contents" />
   </form>

</body> </html>

File: Default.aspx.cs 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; public partial class PreserveMembers : System.Web.UI.Page { 

 private string contents;
   protected void Page_Load(object sender, EventArgs e)
   {
   if (this.IsPostBack)
   {
     contents = (string)ViewState["contents"];
   }
   }
 protected void Page_PreRender(Object sender, EventArgs e)
 {
   ViewState["contents"] = contents;
 }
 protected void cmdSave_Click(object sender, EventArgs e)
 {
   contents = txtValue.Text;
   txtValue.Text = "";
 }
 protected void cmdLoad_Click(object sender, EventArgs e)
 {
   txtValue.Text = contents;
 }

}</source>


Track Your Viewstate

   <source lang="csharp">

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" 

   Inherits="Default" Theme="Core35-Basic" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" > <head runat="server"> 

   <title>Track Your Viewstate</title>

</head> <body> 

   <form id="form1" runat="server">

       <asp:Button ID="Button1" runat="server" Text="Post back..." OnClick="Button1_Click" />
       

       


   </form>

</body> </html> File: Default.aspx.cs 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.HtmlControls;

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

 protected void Page_PreInit(object sender, EventArgs e)
 {
   this.TraceEnabled = true;
 }
   protected void Page_Init(object sender, EventArgs e)
 {
   if (!IsPostBack)
   {
     this.ViewState["MyData"] = "Hello, world";
   }
   Trace.Warn("[MyData] now contains", (string) ViewState["MyData"]);
 }
 
   protected void Page_Load(object sender, EventArgs e)
 {
   Trace.Warn("[MyData] now contains", (string)ViewState["MyData"]);
 }

}</source>


Use ViewState to create a simple counter (C#)

   <source lang="csharp">

File: Default.aspx <%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="SimpleCounter" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" > <head runat="server"> 

   <title>Untitled Page</title>

</head> <body> 

   <form id="form1" runat="server">

       <asp:Button ID="cmdIncrement" 
                   runat="server" 
                   OnClick="cmdIncrement_Click" 
                   Text="Increment" />
<asp:Label ID="lblCount" runat="server"></asp:Label> 
   </form>

</body> </html>

File: Default.aspx.cs 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; public partial class SimpleCounter : System.Web.UI.Page { 

 protected void cmdIncrement_Click(object sender, EventArgs e)
 {
       int counter;
       if (ViewState["Counter"] == null)
       {
           counter = 1;
       }
       else
       {
           counter = (int)ViewState["Counter"] + 1;
       }
       ViewState["Counter"] = counter;
       lblCount.Text = "Counter: " + counter.ToString();
 }

}</source>


Use ViewState to store random data

   <source lang="csharp">

<%@ Page Language="C#" AutoEventWireup="true" 

CodeFile="Default.aspx.cs" Inherits="ViewStateChunking" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" > <head runat="server"> 

   <title>Untitled Page</title>

</head> <body> 

   <form id="form1" runat="server">

       Use View --> Source to see the view
state of this page.
   </form>

</body> </html> File: Default.aspx.cs

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; public partial class ViewStateChunking : System.Web.UI.Page { 

   protected void Page_Load(object sender, EventArgs e)
   {
   Random rnd = new Random();
   byte[] buffer = new byte[1050];
   rnd.NextBytes(buffer);
   ViewState["Data"] = buffer;
   }

}</source>


Visualize the current Base64-encoded contents of the view state

   <source lang="csharp">

<%@ Page Language="C#" AutoEventWireup="true" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" > <head runat="server"> 

   <title>Try to Break Your Viewstate</title>

</head> <script language="javascript"> 

 function ShowViewState()
 {
   var buf = document.forms[0]["__VIEWSTATE"].value;
   var o = document.forms[0]["ViewStateBox"];
   o.value = buf;
 }
 function UpdateViewState()
 {
   var o = document.forms[0]["ViewStateBox"];
   var viewstate = document.forms[0]["__VIEWSTATE"];
   viewstate.value = o.value;
 }

</script> <body> 

    <form id="form1" runat="server">

           <input onclick="ShowViewState()" type="button" value="Display View State" style="width:200px" /> 
           <input onclick="UpdateViewState()" type="button" value="Update View State" style="width:200px" />

Here"s Your (Encoded) ViewState

       <asp:TextBox id="ViewStateBox" runat="server" TextMode="MultiLine" Width="100%" Height="250px"></asp:TextBox>
       <asp:Button id="Button1" runat="server" Text="Post Back..."></asp:Button>

   </form>

</body> </html></source>

Источник — «http://nfex.ru/index.php?title=ASP.NET_Tutorial/Page_Lifecycle/ViewState&oldid=3215»