Maintaining StateMaintaining StateMacDonald Ch. 9MacDonald Ch. 9

MIS 324

Professor Sandvig

Maintaining StateMaintaining State

Tools:Tools:1.1. Cookies Cookies

2.2. ViewstateViewstate

3.3. SessionSession

4.4. CacheCache

1. Cookies1. Cookies Small text files stored on user’s computerSmall text files stored on user’s computer

Useful for storing:Useful for storing: Date of last visitDate of last visit Unique user identifierUnique user identifier PreferencesPreferences etc. etc.

LimitationsLimitations Not secure – user can view, modify, deleteNot secure – user can view, modify, delete User can disableUser can disable

1. Cookies1. Cookies Write:Write:

Single value per cookie:Single value per cookie:• Response.Cookies[“Name”].Value = “Bart”;Response.Cookies[“Name”].Value = “Bart”;

Multiple values per cookieMultiple values per cookie• Response.Cookies[“Name”][“First”] = “Bart”;Response.Cookies[“Name”][“First”] = “Bart”;• Response.Cookies[“Name”][“Last”] = “Simpson”;Response.Cookies[“Name”][“Last”] = “Simpson”;

•

Read Read Request.Cookies[“Name”].Value;Request.Cookies[“Name”].Value; Request.Cookies[“Name”][“First”].Value;Request.Cookies[“Name”][“First”].Value;

1. Cookies1. Cookies

Expiration:Expiration: Default: when browser is closedDefault: when browser is closed

Response.Cookies[“CookieName”].Expires = Response.Cookies[“CookieName”].Expires = DateTime.Now.AddDays(180);DateTime.Now.AddDays(180);

Delete Cookie: set expiration to past (-1)Delete Cookie: set expiration to past (-1)

1. Cookies1. Cookies

Testing for cookieTesting for cookie Attempt to read a cookie that is not present:Attempt to read a cookie that is not present:

Error: Object reference not set to an instance of an object

Solution: Solution: If (Request.Cookies[“Name”] != null) {If (Request.Cookies[“Name”] != null) { //safe to read cookie //safe to read cookie

name = Request.Cookies[“Name”] .Value;name = Request.Cookies[“Name”] .Value;}}

1. Cookies1. Cookies

Benefits:Benefits: Persist between sessionsPersist between sessions Keep track of usernames, last visit, etc.Keep track of usernames, last visit, etc. Easy to useEasy to use

Drawbacks:Drawbacks: Client can blockClient can block Not secureNot secure

2. Viewstate2. Viewstate

Data in web controls automatically storedData in web controls automatically stored Encoded in hidden form fieldEncoded in hidden form field

May add to viewstate programmaticallyMay add to viewstate programmatically ViewState[“UserID”] = “333”;ViewState[“UserID”] = “333”;

Retrieve with same syntaxRetrieve with same syntax Returned datatype is objectReturned datatype is object

• Must convert Must convert int intUserID = Convert.ToInt32(ViewState["UserID"]);int intUserID = Convert.ToInt32(ViewState["UserID"]);

ViewStateViewState Benefits:Benefits:

Very convenientVery convenient Can access data even when controls hiddenCan access data even when controls hidden

DrawbackDrawback Difficult to transfer between pagesDifficult to transfer between pages Does not persist between sessionsDoes not persist between sessions

3. Sessions3. Sessions Data stored on serverData stored on server Unique to each userUnique to each user Uses cookie to associate with userUses cookie to associate with user

User must have cookies enabledUser must have cookies enabled

Create:Create: Session[“LastName”] = “Simpson”;Session[“LastName”] = “Simpson”;

DeleteDelete Session.Abandon; – Deletes the sessionSession.Abandon; – Deletes the session Session.Remove[“LastName”]; – removes itemsSession.Remove[“LastName”]; – removes items

SessionsSessions ExpirationExpiration

Default: 20 minutesDefault: 20 minutes Session.Timeout = 60;Session.Timeout = 60;

BenefitsBenefits SecureSecure

• Client cannot view, edit, deleteClient cannot view, edit, delete Automatic timeoutAutomatic timeout

DrawbacksDrawbacks Do not persistDo not persist Require cookiesRequire cookies Use server resourcesUse server resources

4. Cache4. Cache

Stored on serverStored on server ApplicationApplication

Often used to cache dataOften used to cache data Example: Example: XML Music

Store any type of data / objectStore any type of data / object Stored as type “object”Stored as type “object” Recast when retrievedRecast when retrieved

CacheCache

Add item to cache:Add item to cache: Cache.Insert(“key”, object, dependency, Cache.Insert(“key”, object, dependency,

absoluteExpiration, slidingExpiration) absoluteExpiration, slidingExpiration)

Example:Example: Cache.Insert(“cat30”, “apples”, null,Cache.Insert(“cat30”, “apples”, null,

DateTime.Now.AddSeconds(60), DateTime.Now.AddSeconds(60), Cache.NoSlidingExpiration)Cache.NoSlidingExpiration)

CacheCache

Retrieve:Retrieve:If (Cache[“cat30”] != null) {If (Cache[“cat30”] != null) {

string fruit = (string) Cache[“cat30”];string fruit = (string) Cache[“cat30”];

}}

CacheCache

Benefits:Benefits: SecureSecure Many expiration optionsMany expiration options Store any objectStore any object

Drawbacks:Drawbacks: ????

When to use each:When to use each:Cookies • Need data to persist across sessions

• Security not important

Viewstate • Data associated with page• Similar to hidden form field

Session • Secure• Associated with each user session

Cache • Secure• Share data across sessions• Control expiration

Example: output (source)

SummarySummary Maintaining state:Maintaining state:

Method depends on needsMethod depends on needs

Several flexible alternativesSeveral flexible alternatives