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State management


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State management

  1. 1. Training on State Management<br />Introducing State Management<br />byPraveen Nandagiri<br />
  2. 2. Introducing State Management <br /> Agenda<br /> what is State Management<br /> Client side state management<br /> view sate<br /> control state<br /> Hidden fields<br /> cookies<br /> Query strings<br /> Server side state management<br /> Application sate<br /> Session State<br />
  3. 3. Introducing State Management <br />State management <br />State management is the process by which you maintain state and page information over multiple requests for the same or different pages.<br /> Web pages rarely be stand alone. Web applications almost always need to track users who visits multiple pages, whether to provide personalization, store information about a user or to track usage for reporting purposes.<br />
  4. 4. Introducing State Management <br />Client – Side State Management<br /> This stores information on the client's computer by embedding the information into a Web page, a uniform resource locator(url), or a cookie. The techniques available to store the state <br />The techniques available to store the state information at the client end are listed down below: <br />View State <br />Asp.Net uses View State to track the values in the Controls. You can add custom values to the view state. It is used by the page framework to automatically save the values of the page and of each control just prior to rendering to the page. When the page is posted, one of the first tasks performed by page processing is to restore view state. <br />
  5. 5. Introducing State Management <br />b. Control State <br />If you create a custom control that requires view state to work properly, you should use control state to ensure other developers don’t break your control by disabling view state. <br />c. Hidden fields <br /> Like view state, hidden fields store data in an HTML form without displaying it in the user's browser. The data is available only when the form is processed. <br />d. Cookies<br /> Cookies store a value in the user's browser that the browser sends with every page request to the same server. Cookies are the best way to store state data that must be available for multiple Web pages on a web site. <br />
  6. 6. Introducing State Management <br />e. Query Strings<br /> Query strings store values in the URL that are visible to the user. Use query strings when you want a user to be able to e-mail or instant message state data with a URL. <br />
  7. 7. Introducing State Management <br />2. Server – Side State Management<br /> a. Application State<br />Application State information is available to all pages, regardless of which user requests a page. <br />b. Session State <br />Session State information is available to all pages opened by a user during a single visit. <br />Both application state and session state information is lost when the application restarts. To persist user data between application restarts, you can store it using profile properties. <br />
  8. 8. Introducing State Management <br />Client side management <br /> a) ViewState<br />ASP.Net technology provides View State feature to the web forms. View State is used to remember controls state when page is posted back to server. ASP.Net stores view state on client site in hidden fields and ViewState is in encrypted form. When page is created on web sever this hidden control is populate with state of the controls and when page is posted back to server this information is retrieved and assigned to controls. You can look at this field by looking at the source of the page (i.e by right clicking on page and selecting view source option.)<br />
  9. 9. Introducing State Management <br />The following code sample demonstrates how view state adds data as a hidden form within a Web page’s HTML:<br /><input type="hidden" name="__VIEWSTATE“ id="__VIEWSTATE” value="/wEPDwUKMTIxNDIyOTM0Mg9kFgICAw9kFgICAQ8PFgIeBFRleHQFEzQvNS8yMDA2IDE6Mzc6MTEgUE1kZGROWHn/rt75XF/pMGnqjqHlH66cdw==" /><br />Encrypting of the View State: <br /> You can enable view state encryption to make it more difficult for attackers and malicious users to directly read view state information. Though this adds processing overhead to the Web server, it supports in storing confidential information in view state. <br />
  10. 10. Introducing State Management <br />To configure view state encryption for an application does the following: <br />(in the web.config file)<br /><Configuration><br /> <system.web> <br /><pages viewStateEncryptionMode="Always"/> <br /> </system.web> <br /></configuration><br /> Alternatively, you can enable view state encryption for a specific page by setting the value in the page directive, as the following sample demonstrates: <br /> <%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" ViewStateEncryptionMode="Always"%> <br />
  11. 11. Introducing State Management <br /> You do not need to worry about this as this is automatically handled by ASP.Net. You can enable and disable view state behaviour of page and its control by specifying 'enableViewState' property to true and false. You can also store custom information in the view state as described in following code sample. This information can be used in round trips to the web server.<br /> Ex : <form id="form1" runat="server" enableviewstate="true"><br />Example :<br /> //To Save Information in View State ViewState.Add ("NickName", "David");//Retrieving View stateString strNickName = ViewState ["NickName"];<br />
  12. 12. Introducing State Management <br />b)Control State <br /> If you create a custom control that requires ViewState, you can use the ControlState property to store state information for your control. ControlState allows you to persist property information that is specific to a control and cannot be turned off like the ViewState property. To use control state in a custom control, your control must override the OnInit method and call the Register-RequiresControlState method during initialization and then override the SaveControl-State and LoadControlState methods. <br /> Use control state only for small amounts of critical data that are essential for the control across postbacks. Do not use control state as an alternative to view state.<br />
  13. 13. Introducing State Management <br />The differences between Control state and view state <br /> 1. Control state, introduced in ASP.NET version 2.0, is similar to view state but functionally independent of view state. <br /> 2. A page developer can disable view state for the page or for an individual control for performance. However, control state cannot be disabled.<br /> 3. Control state is designed for storing a control's essential data that must be available on postback to enable the control to function even when view state has been disabled. <br /> 4. By default,the ASP.NET page framework stores control state in the page in the same hidden element in which it stores view state.<br /> 5. Even if view state is disabled, or when state is managed using Session, control state travels to the client and back to the server in the page.<br /> 6. On postback, ASP.NET deserializes the contents of the hidden element and loads control state into each control that is registered for control state.<br /> 7. Use control state only for small amounts of critical data that are essential for the control across postbacks.Do not use control state as an alternative to view state<br />
  14. 14. Introducing State Management <br />c)Hidden fields: <br />ViewState stores information in the Web page using hidden fields. Hidden fields are sent back to the server when the user submits a form; however, the information is never displayed by the Web browser (unless the user chooses to view the page source). ASP.NET allows you to create your own custom hidden fields and store values that are submitted with other form data. A HiddenField control stores a single variable in its Value property and must be explicitly added to the page. You can use hidden fields only to store information for a single page, so it is not useful for storing session data. If you use hidden fields, you must submit your pages to the server using Hypertext Transfer Protocol (HTTP) POST (which happens if the user presses a button) rather than requesting the page using HTTP GET (which happens if the user clicks a link). Unlike view state data, hidden fields have no built-in compression, encryption, hashing, or chunking, so users can view or modify data stored in hidden fields. <br />
  15. 15. Introducing State Management <br />ASP.Net provides HtmlInputControl that offers hidden field functionality.<br />Example :<br /> //Declaring a hidden variable protected HtmlInputHiddenhidNickName;//Populating hidden variable(asign a value to hidden variable)hidNickName.Value = "Page No 1";//Retrieving value stored in hidden field.string str = hidNickName.Value; <br />Note : Critical information should not be stored in hidden fields.<br />
  16. 16. Introducing State Management <br />d)Cookies <br /> Web applications can store small pieces of data in the client’s Web browser by using cookies. A cookie is a small amount of data that is stored either in a text file on the client file system (if the cookie is persistent) or in memory in the client browser session (if the cookie is temporary). The most common use of cookies is to identify a single user as he or she visits <br />
  17. 17. Introducing State Management <br />Reading and Writing Cookies:<br /> It should be noted that cookies are generally used for storing only small amount of data (i.e 1-10 KB).<br /> Example :<br /> //Storing value in cookie HttpCookie cookie = new HttpCookie("NickName");cookie.Value = "David";Request.Cookies.Add(cookie); //Retrieving value in cookie if (Request.Cookies.Count > 0 && Request.Cookies["NickName"] != null)         lblNickName.Text = "Welcome" + Request.Cookies["NickName"].ToString();else         lblNickName.Text = "Welcome Guest"; <br /> Cookies can be permanent in nature or temporary. ASP.Net internally stores temporary cookie at the client side for storing session identifier. By default cookies are temporary and permanent cookie can be placed by setting "Expires" property of the cookie object.<br /> If you do not define the Expires property, the browser stores it in memory and the cookie is lost if the user closes his or her browser. <br />
  18. 18. Introducing State Management <br /> e) Query Strings:<br />Query strings are commonly used to store variables that identify specific pages, such as search terms or page numbers. A query string is information that is appended to the end of a page URL. A typical query string might look like the following real-world example: In this example, the URL identifies the Default.aspx page. The query string (which starts with a question mark [?]) contains a single parameter named “kbid,” and a value for that parameter, “315233.” Query strings can also have multiple parameters, such as the following real-world URL, which specifies a language and query when searching the Web site: Value Name | ASP.NET Object | Value mkt | Request.QueryString[“mkt”] | en-US setlang | Request.QueryString[“setlang”] | en-US q | Request.QueryString[“q”] | hello world <br />
  19. 19. Introducing State Management <br />Limitations for Query Strings:1. Some Browsers and client devices impose a 2083 – character limit on the length of the URL. 2. You must submit the page using an HTTP GET command in order for query string values to be available during page processing. Therefore, you shouldn’t add query strings to button targets in forms. 3. You must manually add query string values to every hyperlink that the user might click. Example: <br /> Label1.Text = "User: " + Server.HtmlEncode(Request.QueryString["user"]) + ", Prefs: " + Server.HtmlEncode(Request.QueryString["prefs"]) + <br />", Page: " + Server.HtmlEncode(Request.QueryString["page"]); <br />
  20. 20. Introducing State Management <br />Server - Side State Management:a)Application State: <br />Application State is used to store information which is shared among users of the ASP.Net web application. Application state is stored in the memory of the windows process which is processing user requests on the web server. Application state is useful in storing small amount of often-used data. If application state is used for such data instead of frequent trips to database, then it increases the response time/performance of the web application.<br /> In ASP.Net, application state is an instance of HttpApplicationState class and it exposes key-value pairs to store information. Its instance is automatically created when a first request is made to web application by any user and same state object is being shared across all subsequent users.<br />
  21. 21. Introducing State Management <br /> Application state can be used in similar manner as session state but it should be noted that many user might be accessing application state simultaneously so any call to application state object needs to be thread safe. This can be easily achieved in ASP.Net by using lock keyword on the statements which are accessing application state object. This lock keyword places a mutually exclusive lock on the statements and only allows a single thread to access the application state at a time. Following is an example of using application state in an application.<br />Example :<br /> //Stroing information in application statelock (this) {        Application["NickName"] = "David"; } //Retrieving value from application statelock (this) {       string str = Application["NickName"].ToString(); } <br />
  22. 22. Introducing State Management <br />b) Session State:<br /> Session state is used to store and retrieve information about the user as user navigates from one page to another page in ASP.Net web application. Session state is maintained per user basis in ASPNet runtime. It can be of two types in-memory and out of memory. In most of the cases small web applications in-memory session state is used. Out of process session state management technique is used for the high traffic web applications or large applications. It can be configured  with some configuration settings in web.conig file to store state information in ASPNetState.exe (windows service exposed in .Net or on SQL server.)<br />
  23. 23. Introducing State Management <br />In-memory Session state can be used in following manner<br />Example :<br /> //Storing informaton in session state Session["NickName"] = "Ambuj";//Retrieving information from session statestring str = Session["NickName"]; <br /> Session state is being maintained automatically by ASP.Net. A new session is started when a new user sents  first request to the server. At that time session state is created and user can use it to store information and retrieve it while navigating to different web pages in ASP.Net web application.<br />ASP.Net maintains session information using the session identifier which is being transacted b/w user machine and web server on each and every request either using cookies or querystring (if cookieless session is used in web application).<br /> So, In the above illustrations, we understood the practical concepts of using different state management techniques in ASP.Nettechonology.<br />
  24. 24. Introducing State Management <br />Advantages of Client – Side State Management:1. Better Scalability: With server-side state management, each client that connects to the Web server consumes memory on the Web server. If a Web site has hundreds or thousands of simultaneous users, the memory consumed by storing state management information can become a limiting factor. Pushing this burden to the clients removes that potential bottleneck. 2. Supports multiple Web servers: With client-side state management, you can distribute incoming requests across multiple Web servers with no changes to your application because the client provides all the information the Web server needs to process the request. With server-side state management, if a client switches servers in the middle of the session, the new server does not necessarily have access to the client’s state information. You can use multiple servers with server-side state management, but you need either intelligent load-balancing (to always forward requests from a client to the same server) or centralized state management (where state is stored in a central database that all Web servers access). <br />
  25. 25. Introducing State Management <br />Advantages of Server – Side State Management:1. Better security: Client-side state management information can be captured (either in transit or while it is stored on the client) or maliciously modified. Therefore, you should never use client-side state management to store confidential information, such as a password, authorization level, or authentication status. 2. Reduced bandwidth: If you store large amounts of state management information, sending that information back and forth to the client can increase bandwidth utilization and page load times, potentially increasing your costs and reducing scalability. The increased bandwidth usage affects mobile clients most of all, because they often have very slow connections. Instead, you should store large amounts of state management data (say, more than 1 KB) on the server. <br />
  26. 26. Thank You !<br />