State Management

Question

Hi Ques What is the State Management ? How many types of State Management ?

Satyapriya Nayak · Answer

Hi Arun State management is the process by which you maintain state and page information over multiple requests for the same or different pages. Types of State Management There are 2 types State Management: 1.Client – Side State Management 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 information at the client end are listed down below: a. View State – 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 Asp.net 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. b. Control State – 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. c. Hidden fields – 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. d. Cookies – 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. e. Query Strings - 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. 2.Server – Side State Management a.Application State - Application State information is available to all pages regardless of which user requests a page. b.Session State – Session State information is available to all pages opened by a user during a single visit. 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. Implementation Procedure Client – Side State Management: View State: The ViewState property provides a dictionary object for retaining values between multiple requests for the same page. When an ASP.NET page is processed the current state of the page and controls is hashed into a string and saved in the page as a hidden field. If the data is too long for a single field then ASP.NET performs view state chunking (new in ASP.NET 2.0) to split it across multiple hidden fields. The following code sample demonstrates how view state adds data as a hidden form within a Web page's HTML: Encrypting of the View State: 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. To configure view state encryption for an application does the following: Alternatively you can enable view state encryption for a specific page by setting the value in the page directive as the following sample demonstrates: View State is enabled by default but if you can disable it by setting the EnableViewState property for each web control to false. This reduces the server processing time and decreases page size. Reading and Writing Custom View State Data: If you have a value that you'd like to keep track of while the user is visiting a single ASP.NET Web page adding a custom value to ViewState is the most efficient and secure way to do that. However ViewState is lost if the user visits a different Web page so it is useful only for temporarily storing values. Example: Determine the time of last visit to the page // Check if View State object exists and display it if it does If (ViewState [lastVisit]!= null) Label1.Text = (string)ViewState[lastVisit]; else Label1.Text = lastVisit ViewState not defined.; // Define the ViewState object for the next page view ViewState.Add(lastVisit DateTime.Now.ToString()); Control State: 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. Hidden fields: 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. Cookies: 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 multiple Web pages. Reading and Writing Cookies: A Web application creates a cookie by sending it to the client as a header in an HTTP response. The Web browser then submits the same cookie to the server with every new request. Create a cookie -> add a value to the Response.Cookies HttpCookieCollection. Read a cookie -> read values in Request.Cookies. Example: // Check if cookie exists and display it if it does if (Request.Cookies[lastVisit] != null) // Encode the cookie in case the cookie contains client-side script Label1.Text = Server.HtmlEncode(Request.Cookies[lastVisit].Value); else Label1.Text = No value defined; // Define the cookie for the next visit Response.Cookies[lastVisit].Value = DateTime.Now.ToString();Response.Cookies[lastVisit].Expires = DateTime.Now.AddDays(1); 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. To delete a cookie overwrite the cookie and set an expiration date in the past. You can't directly delete cookies because they are stored on the client's computer. Controlling the Cookie Scope: By default browsers won't send a cookie to a Web site with a different hostname. You can control a cookie's scope to either limit the scope to a specific folder on the Web server or expand the scope to any server in a domain. To limit the scope of a cookie to a folder set the Path property as the following example demonstrates: Example: Response.Cookies[lastVisit].Path = /Application1; Through this the scope is limited to the /Application1 folder that is the browser submits the cookie to any page with in this folder and not to pages in other folders even if the folder is in the same server. We can expand the scope to a particular domain using the following statement: Example: Response.Cookies[lastVisit].Domain = Contoso; Storing Multiple Values in a Cookie: Though it depends on the browser you typically can't store more than 20 cookies per site and each cookie can be a maximum of 4 KB in length. To work around the 20-cookie limit you can store multiple values in a cookie as the following code demonstrates: Example: Response.Cookies[info][visit].Value = DateTime.Now.ToString(); Response.Cookies[info][firstName].Value = Tony; Response.Cookies[info][border].Value = blue; Response.Cookies[info].Expires = DateTime.Now.AddDays(1); Running the code in this example sends a cookie with the following value to the Web browser: (visit=4/5/2006 2:35:18 PM) (firstName=Tony) (border=blue) Query Strings: 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: http://support.microsoft.com/Default.aspx?kbid=315233 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 Microsoft.com Web site: http://search.microsoft.com/results.aspx?mkt=en-US&setlang=en-US&q=hello+world Value Name| ASP.NET Object | Value mkt | Request.QueryString[mkt] | en-US setlang | Request.QueryString[setlang]| en-US q | Request.QueryString[q] | hello world 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: Label1.Text = User:  + Server.HtmlEncode(Request.QueryString[user]) +  Prefs:  + Server.HtmlEncode(Request.QueryString[prefs]) +  Page:  + Server.HtmlEncode(Request.QueryString[page]); Server - Side State Management: Application State: ASP.NET allows you to save values using application state a global storage mechanism that is accessible from all pages in the Web application. Application state is stored in the Application key/value dictionary. Once you add your application-specific information to application state the server manages it and it is never exposed to the client. Application state is a great place to store information that is not user-specific. By storing it in the application state all pages can access data from a single location in memory rather than keeping separate copies of the data. Data stored in the Application object is not permanent and is lost any time the application is restarted. ASP.NET provides three events that enable you to initialize Application variables (free resources when the application shuts down) and respond to Application errors: a.Application_Start: Raised when the application starts. This is the perfect place to initialize Application variables. b.Application_End: Raised when an application shuts down. Use this to free application resources and perform logging. c.Application_Error: Raised when an unhandled error occurs. Use this to perform error logging. Session State: ASP.NET allows you to save values using session state a storage mechanism that is accessible from all pages requested by a single Web browser session. Therefore you can use session state to store user-specific information. Session state is similar to application state except that it is scoped to the current browser session. If different users are using your application each user session has a different session state. In addition if a user leaves your application and then returns later after the session timeout period session state information is lost and a new session is created for the user. Session state is stored in the Session key/value dictionary. You can use session state to accomplish the following tasks: i. Uniquely identify browser or client-device requests and map them to individual session instances on the server. This allows you to track which pages a user saw on your site during a specific visit. ii. Store session-specific data on the server for use across multiple browser or client-device requests during the same session. This is perfect for storing shopping cart information. iii.Raise appropriate session management events. In addition you can write application code leveraging these events. ASP.NET session state supports several different storage options for session data: a. InProc Stores session state in memory on the Web server. This is the default and it offers much better performance than using the ASP.NET state service or storing state information in a database server. InProc is fine for simple applications but robust applications that use multiple Web servers or must persist session data between application restarts should use State Server or SQLServer. b. StateServer Stores session state in a service called the ASP.NET State Service. This ensures that session state is preserved if the Web application is restarted and also makes session state available to multiple Web servers in a Web farm. ASP.NET State Service is included with any computer set up to run ASP.NET Web applications; however the service is set up to start manually by default. Therefore when configuring the ASP.NET State Service you must set the startup type to Automatic. c. SQLServer Stores session state in a SQL Server database. This ensures that session state is preserved if the Web application is restarted and also makes session state available to multiple Web servers in a Web farm. On the same hardware the ASP.NET State Service outperforms SQLServer. However a SQL Server database offers more robust data integrity and reporting capabilities. d.Custom Enables you to specify a custom storage provider. You also need to implement the custom storage provider. e.Off Disables session state. You should disable session state if you are not using it to improve performance. Advantages 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). 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. Please refer the below links http://www.c-sharpcorner.com/uploadfile/nipuntomar/state-management-in-Asp-Net/default.aspx http://www.dotnetfunda.com/articles/article61.aspx http://www.codeproject.com/Articles/31994/Beginners-Introduction-to-State-Management-Techniq http://www.informit.com/articles/article.aspx?p=31842 Thanks

Saroj Kumar Sahu · Answer

Please refer the below links http://www.codeproject.com/Articles/31344/Beginner-s-Guide-To-View-State http://www.codeproject.com/Articles/31994/Beginners-Introduction-to-State-Management-Techniq

Senthilkumar · Answer

Hi ASP.Net provides the statement management mechanism to store the state and retrieve across the post backs. The ASP.Net web page is stateless because the state of the control across the post backs are not persisted in the asp.net There is some mechanism needed to maintain and retain the state. There are two state management techniques. 1) Client side state management 2) Server side state management Client Side state management: It will maintain the state management in the client side. It may be in the client browser or the memory of the client side. It is light weight and it will avoid the addition overhead on the server side. But there are some security risks as well. 1) View state - It stores on the hidden field and it will do encrypt and decrypt the data every time before store and retrieve across the post backs. This will be stored in the client browser .ie hidden field. It may be tampered by the hackers. 2) Control state - 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. 3) Query string - The query string can be passed along with the client browser url and it is limited upto 255. It can be encrypt to send other pages 4) hidden fields - The hidden fields are not visible to the users in the web page and can be store and retrieve. It can retain the value by default across the post backs. 5) cookies - This will be stored in the browser (temp files) and it can be set the expiration policy. Some of the browsers may not support or it may be in disabled state. It prefers to store the small amount of data. Mostly the login credentials will be stored. Server Side state management: The server side state mechanism ensures the data will not be lost and it will be stored in the processor memory or the sql server. It can be used to transfer the data across the pages. 1) session state: Session is server state mechanism and it is used to store the data in the memory. It is persisted across the post backs and it can be used to transfer between the pages. It is bit costly in terms of usage because it stores data as object in the serialized format. So it needs serialize and deserialize every time whenever we store and retrieves. The session data can be shared only for the current user. It can be shared across the pages for the current logged session. It is very easy to use. Session[Key] = value; It has the key and value combination. The value can be retrieved and rewritten using the session key. The session can be abondan and killed by using key. There are three session states. 1) InProc - Processor memory(IIS) 2) OutProc - state server 2) SqlServer - Session data will be stored in the sql server database Drawbacks: ----------- - Increase page pay load - Additional overhead while serialize and deserialize - Increase memory allocations to the server - Microsoft suggest to use the control state rather than view state. Real time example: ------------------ Once the user logged in you may need to get more details about that user to show in many place. Like show the full name or last logged in details email id. It may need in many pages but it cannot be retrieve every time from the database. It has to be queried once and result should be stored in session object. Whenever we need user details information in the pages it can be read from the session rather than database. 2) Application state: The Application state is used to store the state and will be used across the users and across the pages. It has to be set in the application level event like global.asax. It uses the key and value format. Application[Version] = 2.1; 3)Profile Properties: ASP.NET provides a feature called profile properties which allows you to store user-specific data. This feature is similar to session state except that the profile data is not lost when a user's session expires. The profile-properties feature uses an ASP.NET profile which is stored in a persistent format and associated with an individual user. The ASP.NET profile allows you to easily manage user information without requiring you to create and maintain your own database. In addition the profile makes the user information available using a strongly typed API that you can access from anywhere in your application. You can store objects of any type in the profile. The ASP.NET profile feature provides a generic storage system that allows you to define and maintain almost any kind of data while still making the data available in a type-safe manner. For more info: http://msdn.microsoft.com/en-us/library/75x4ha6s.aspx