Wednesday, 28 March 2018

012 Asp.Net State Management

Asp.Net Page render html to browser . Each time a new page is requested , html and class created newly .When a page is posted to the server , all information enter in the browser interface lost. For example, if you have enter text in a textbox and the page is posted to the server ,  after the page make round trip , textbox text will lost data. To avoid this, Asp.Net introduce some new functionality, call State Management .There are several techniques to manage State. ASP.NET allow State Management  Client and Server , both ways. 

Here is a list of Client side and Server side  State Management techniques as follows. 

Client side
  1.     Hidden Field
  2.     View State
  3.     Cookies
  4.     Control State
  5.     Query Strings

 Server side
  1.     Session
  2.     Application




Hidden Field : Hidden field is Asp.Net controls which are not visible in browser. Hidden field are fully Programmable and Manageable. Hidden field can retain its value, after page have made round trip. Each hidden field can store one value . Asp.Net page can hold multiple hidden field.When a page is posted to the server , hidden field also post with other control collection . After the postback , hidden field retain its information .This functionality is happen on HTTP POST the server.


ClientID Gets the control ID for HTML markup that is generated by Server
EnableTheming Gets or sets a value indicating whether themes applicable or not
EnableViewState Gets or sets value indicating server control have view state
ID string to identify a the server control
Value Gets or sets the value of the hidden field
Visible Gets or sets value that control will be visible in browser or not




Example
The follwoing example show , hidden fields 'HiddenField1' is assigned a string in 
button click event and posted to the server ,after postback , value is retain by
'HiddenField1'

Aspx Page

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default3.aspx.cs" Inherits="Default3" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
            <form id="form1" runat="server">
                 <div>
                       <asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />
                 </div>
                      <asp:HiddenField ID="HiddenField1" runat="server" />
           </form>
</body>
</html>


C# Code

using System;
using System.Web.UI.WebControls;

public partial class Default3 : System.Web.UI.Page
{
                 protected void Page_Load(object sender, EventArgs e)
                {
                  if (HiddenField1.Value != null)
                     {
                         string myValue = HiddenField1.Value.ToString();
                         Response.Write(myValue);
                     }
                  }

                 protected void Button1_Click(object sender, EventArgs e)
                 {
                  HiddenField1.Value = "Asp.Net State Management Hidden Field Example";
                 }
}

 Output:
 Asp.Net State Management Hidden Field Example

View State : ViewState is a dictionary object , ViewState retain value in key-value format. Each Asp.Net page may content several ViewState. Whens a page is posted with HTTP post, and load again, ViewState retain  it information  unchanged .When is page is posted to the server, the entire ViewState is hashed  to a long string. This hash value is assigned to a hidden field , in the page initialization stage, this hash value again assigned to the view state.Thus a page restore it's ViewState collection .The following value can be stored in ViewState.

  1. Strings
  2. Integers
  3. Boolean values
  4. Array objects
  5. ArrayList 
  6. Hash tables 
Viewstate can be enable or disable , it can be done for entire application  or page level or control to control.
  •  entire application : To enable or disable ViewState for entire application , you need to write invoice configuration file. Below is the example 

    xml version="1.0"?>
    <configuration>
    <system.web>
    <pages enableViewState="false"/>
    </system.web>
    </configuration>

  • page level : You can also enable or disable  ViewState at page level. At the top of page the code is written, here is a example.

    <%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default3.aspx.cs" Inherits="Default3" EnableViewState="false" %>

  • control : ViewState can be  applicable for single control also. You can  enable or disable View State control to control.        
          <asp:TextBox ID="TextBox1" runat="server" ViewStateMode="Enabled" ></asp:TextBox>
 
StateBag manage ViewState object. Here is some commonly used  attribute of a StateBag.

Type Name What is ?
Property Item(String) Gets or sets the value of an item stored in the StateBag object.
Property Count How many item is there in the StateBag object. 
Property keys Returns the collection of  keys in the StateBag object.
Property value Return the collection of ViewState value.
Method Add(name,value) Add new ViewState Item in StateBag object.
Method Clear Clear ViewState collcetion from StateBag object.
Method Remove Remove ViewState collcetion from StateBag object.

 Example
The follwoing example show , ViewState ,'StateValue' is assigned a string in 
button click event and posted to the server ,after postback , value is retain by
ViewState ,'StateValue'



 Aspx Page
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default3.aspx.cs" Inherits="Default3" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
     <body>
                <form id="form1" runat="server">
                   <div>
                        <asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />
                    </div>
                 </form>
       </body>
</html>




C# Code
using System;
using System.Web.UI.WebControls;

public partial class Default3 : System.Web.UI.Page
{
          protected void Page_Load(object sender, EventArgs e)
        {
           if (ViewState["StateValue"] != null)
           {
                  string myValue = ViewState["StateValue"].ToString();
                  Response.Write(myValue);
            }
       }
       protected void Button1_Click(object sender, EventArgs e)
       {
                ViewState["StateValue"] = "Asp.Net State Management View State Example";
     }
}


Cookies :Cookies are small text file stored in client computer or browser memory. The size of a Cookie is limited and Cookies are not permanent. Cookie has a expiration date of time. A client send some cookie information to the server and server also capable to read the cookies. Cookie Store information small information. A particular site can use multiple cookies. A client can read a control value and assign it to the cookie, the page is then posted to the server, when page is rendered again , server read the cookies assign the value to the respective controls.

Example
The follwoing example show , cookie ,'StateValue' is assigned a string in 
button click event and posted to the server ,after postback , value is retain by
cookie ,'StateValue'

Aspx Page


<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default3.aspx.cs" Inherits="Default3" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
          <body>
                        <form id="form1" runat="server">
                                 <div>
                                        <asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />
                               </div>
                       </form>
          </body>
</html>


C# Code

using System;
using System.Web.UI.WebControls;
using System.Web;

public partial class Default3 : System.Web.UI.Page
{
                protected void Page_Load(object sender, EventArgs e)
                {
                         if (Request.Cookies["StateValue"] != null)
                          {
                               string myValue = Request.Cookies["StateValue"].Value.ToString();
                               Response.Write(myValue);
                        }

              }

                 protected void Button1_Click(object sender, EventArgs e)
                {
                             HttpCookie myCookie = new HttpCookie("StateValue");
                             myCookie.Value = "Asp.Net State Management Cookie Example";
                             myCookie.Expires = DateTime.Now.AddSeconds(10);
                             Response.Cookies.Add(myCookie);
                }
}

Output :
 Asp.Net State Management Cookie Example

A cookie size limits of 4 KB .  Large data cannot be stored in cookie. An user can disable cookie from his Browser and cookie are easily tamperable . There are two types of cookies
persistent cookie and  not persistent cookie.

Persistent cookies : Persistent cookies has expiry date and time.

HttpCookie myCookie = new HttpCookie("myCookie");
myCookie.Value = "Persistance Cookie Example";
myCookie.Expires = DateTime.Now.AddSeconds(100);
Response.Cookies.Add(myCookie);


Non persistent cookie : It exist still the user using browser and do not have any input up expiry date. 
 
Response.Cookies["myCookie"].Value = "Non Persistance Cookie Example";

You need to set ViewState property in the web.Config  file, EnableViewState to true or false.

Here is the example of Web.Config file

xml version="1.0"?>
<configuration>
      <system.web>
         <pages enableViewState="false" />
     </system.web>
</configuration>




Control State :Not yet updated


Query Strings : The query string is one of the technique to pass information from one page to another page. Query string is some additional string  with URL . Query string starts with (?) . A query string has two part,  field and value . Multiple field can be added with  the symbol (&). Query string cannot handle long data. Query string is not safe, it can be easily tamper. To retrieve query the following Syntax is used.

Request.QueryString(variable)[(index)|.Count]


Source.aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Source.aspx.cs" Inherits="Source" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
         </head>
           <body>
                             <form id="form1" runat="server">
                                     <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
                                     <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
                                     <div>
                                     <asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />
                                    </div>
                             </form>
           </body>
</html>

Source.aspx.cs

using System;
using System.Web.UI.WebControls;
using System.Web;

public partial class Source : System.Web.UI.Page
{
              protected void Page_Load(object sender, EventArgs e)
              {
              }
               protected void Button1_Click(object sender, EventArgs e)
               {
                       Response.Redirect("Destination.aspx?Parameter1=" + TextBox1.Text + "&Parameter2=" + TextBox2.Text);
              }
}

Destination.aspx
 
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Destination.aspx.cs" Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
           <body>
                     <form id="form1" runat="server">
                           <div>
                          </div>
                    </form>
          </body>
</html>

Destination.aspx.cs
using System;
using System.Collections.Generic;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page
{
         protected void Page_Load(object sender, EventArgs e)
         {
              string param1 = Request.QueryString["Parameter1"];
              string param2 = Request.QueryString["Parameter2"];

               Response.Write("Parameter1 :" + param1.ToString());
              Response.Write("Parameter1 :" + param2.ToString());
        }
}

Source.aspx




Destination.aspx




Server side

 Session : ASP.NET session state have several different storage options for session data.Option are 
                determined by SessionStateMode enumeration. 

1) InProc mode stores session state in memory on the server. This is the default session state .Store       session state and variable in local Web server.

2) StateServer mode, which stores session state in a separate process. 

Example
xml version="1.0"?>
           <configuration>
                  <system.web>
                               <pages enableViewState="false"/>
                                             <sessionState mode="StateServer"
                                                         stateConnectionString="Your Server IP"
                                                         cookieless="false"
                                                         timeout="20"/>
                  </system.web>
</configuration>

Session is globally unique 120 bit identifier . Sessionid is pass from client to server and server to client. State is managed by HttpSessionState class which comes under System.Web.SessionState

Type Name What is ?
Property Count How many session state is there in the HttpSessionState collection.
Property IsNewSession An indicator which tells that the Session has created in current request or not.
Property Item[Int32] Get or Set Session value with index.
Property Item[String] Get or Set Session value with name.
Property Keys Get collection of keys for all value stored in HttpSessionState.
Property SessionID Unique identifier for session.
Property Timeout Get or Set time limit to terminate a session.
Method Add(String, Object) Add new item to the HttpSessionState.
Method Clear Clear all form HttpSessionState collection.
Method Remove Delete particular item from HttpSessionState collection.
Method RemoveAll Remove all from HttpSessionState collection.



3) SQLServer mode stores session state in a SQL Server database. 

Example
xml version="1.0"?>
<configuration>
               <system.web>
               <pages enableViewState="false"/>
                                        <sessionState mode="SQLServer"
                                             sqlConnectionString="" />
              </system.web>
</configuration>


4) Custom mode, store custom in storage. 

5) Off mode disables session state


Example : How data stored in session variable and retrieve after postback.

Aspx Page

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

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
      <body>
              <form id="form1" runat="server">
               <div>
                        <asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />
               </div>
               <asp:HiddenField ID="HiddenField1" runat="server" />
              </form>
      </body>
</html>



C# Code
using System;
using System.Web.UI.WebControls;
using System.Web;

public partial class Default : System.Web.UI.Page
{
          protected void Page_Load(object sender, EventArgs e)
         {

            if (Session["StateValue"] != null)
            {
              string myValue = Session["StateValue"].ToString();
              Response.Write(myValue);
          }

         }

            protected void Button1_Click(object sender, EventArgs e)
           {
                  Session["StateValue"] = "Asp.Net State Management Session Example";
            }
}

Output :
Asp.Net State Management Session Example

Application :  Application State is a server side State Management technique. The information stored in application state are usable for all user in a particular application .Application state can store only small data . This is called application level state management . Global.asax  is a file which is created automatically  when an Asp.Net application created . This file contain application  event like  Application_Start ,Application_End when application variable is managed . Application variable  clear automatically only when hosting server restart.

Example : The example shows that application variable Name,Roll,Address declared in Global.asax.The value is retrieved in the Default.aspx page .Output has shown below.   

Application State comes under HttpApplicationState . Application State is generally used for site hit count. Formulti client application client name is also assign to the Application State variable and for Multi Language Global  Application , language and currency code sometimes considered in Application State variable. Here are some commonly used attribute for Application State variables. 

Type Name What is ?
Property Count How many item in HttpApplicationState collections.
Property Item[Int32]  Get or Set object on HttpApplicationState by Index.
Property Item[String] Get or Set object on HttpApplicationState by name.
Property Keys Get collection of keys from HttpApplicationState.
     
     Below are the event where related to Application Event.
  • Application_Start
  • Application_End
  • Application_Error
  • Session_Start
  • Session_End
    •  

Global.asax

<%@ Application Language="C#" %>

<script runat="server">

                  void Application_Start(object sender, EventArgs e)
                 {
                              Application["Name"] = "John";
                              Application["Roll"] = "12";
                              Application["Address"] = "3A,CALIFORNIA";

                  }

                   void Application_End(object sender, EventArgs e)
                   {
                           // Code that runs on application shutdown
                           Application.Clear();
                   }
</script>

Default.aspx

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

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
       </head>
          <body>
                    <form id="form1" runat="server">
                      <div>
                       </div>
                    </form>
           </body>
</html>

Default.aspx.cs

using System;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page
{
                       protected void Page_Load(object sender, EventArgs e)
                        {
                                        Response.Write(Application["Name"].ToString());
                                        Response.Write("");
                                        Response.Write(Application["Roll"].ToString());
                                        Response.Write("");
                                        Response.Write(Application["Address"].ToString());
                         }
}


Output :

John
12
3A,CALIFORNIA



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