16 Passing Data between pages Sessions Query Strings
16 – Passing Data between pages: Sessions, Query Strings, & Self Posting Mark Dixon, So. CCE Page 1
Session Aims & Objectives • Aims – To introduce the fundamental ideas involved in passing data between pages • Objectives, by end of this week’s sessions, you should be able to: – pass data between pages, using: • Self Posting • Query Strings • Session Variables Mark Dixon, So. CCE Page 2
Example: Logon • Restrict access to home page Mark Dixon, So. CCE Page 3
Example: Logon - code (v 2) • Using Server-side VB Script: Logon. htm <html> <head> <title></title> </head> Home. htm <html> <head> <title>My Home page</title> </head> <body> <p>Welcome to my home page. <p>Please logon: <img src="You. Are. Here. jpg" WIDTH="450" HEIGHT="2 <form action=Login. Fail. aspx method=post> </body> <input name=txt. User. Name type=text> Login. Fail. aspx </html> <input name=txt. Pass. Word type=text> <html> <input name=btn. Logon type=submit value=Logon> <head> </form> <title></title> </body> <% </html> If Request. Form("txt. User. Name") = "mark" And Request. Form("txt. Pass. Word") = " Response. Redirect("home. htm") End If %> </head> <body> <p>Sorry, those login details were incorrect. <p>Please try <a href=Logon. htm>again</a> </body> </html> Mark Dixon, So. CCE Page 4
Problem • Want restricted access: • However, can type home page directly (bypassing password page) Mark Dixon, So. CCE Page 5
Solution • Need way for: – password page to tell home page – that user logged in OK Mark Dixon, So. CCE Page 6
Passing Data between pages • Problem – want to protect all pages from unauthorised access – need to store record of successful login • Variables – only persist for duration of page Mark Dixon, So. CCE Page 7
Passing Data (persistent) • Cookies (not covered in Soft 131) – stored on users’ (client) hard drive – persists between sessions • Database/file (covered in next lecture) – stored on server hard drive – persists between sessions Mark Dixon, So. CCE Page 8
Passing Data (temporary) • Session object – exists for current session – clears if user closes browser – clears after 20 mins of inactivity • Forms and Self Posting • Query Strings – Useful for passing information between pages Mark Dixon, So. CCE Page 9
Example: Logon - code (v 3) • Using Session variable: Logon. htm <html> <head> <title></title> </head> Home. aspx <html> <head> <title>My Home page</title> <% If Session("Logged. In") <> "Yes" Then Response. Redirect("Logon. htm") End If %> </head> <body> <p>Please logon: <p>Welcome to my home page. <form action=Login. Fail. aspx method=post> <img src="You. Are. Here. jpg" WIDTH="450" HEIGHT="2 <input name=txt. User. Name type=text> Login. Fail. aspx </body> <input name=txt. Pass. Word type=text> </html> <input name=btn. Logon type=submit value=Logon> <head> </form> <title></title> </body> <% </html> If Request. Form("txt. User. Name") = "mark" And Request. Form("txt. Pass. Word") = " Session("Logged. In") = "Yes" Response. Redirect("home. htm") End If %> </head> Mark Dixon, So. CCE <body> <p>Sorry, those login details were incorrect. <p>Please try <a href=Logon. htm>again</a> </body> </html> Page 10
Maintaining State: Session Object • Session variable – all strings <html> <head> <title>Login</title> </head> <body> Login. aspx <% If Request. Form("txt. User. Name") = "George" Then • Abandon method – deletes all session variables • Redirect method – redirects browser to specified page Mark Dixon, So. CCE Session("Login. OK") = "Yes" Response. Redirect("Home. aspx") Else Session. Abandon() If Request. Form("txt. User. Name") <> "" Then Response. Write("Invalid user name, please try End If %> <p>Please login: <form name="frm. Login" action="Login. asp" method=post> Username: <input name="txt. User. Name" type="text"> Password: <input name="txt. Pass. Word" type="password"> <input name="btn. Login" type="submit" value="Login"> </form> </body> </html> Page 11
Maintaining State: Session Object Home. aspx <html> <head> <title></title> <% ASP code to If Session("Login. OK") <> "Yes" Then Response. Redirect("Login. aspx")check for successful login End If %> </head> <body> <center><b>Home Page</b></center> <p>Welcome to my home page. </body> </html> Mark Dixon, So. CCE Page 12
Maintaining State: Self Posting • Form points to self: • If any submit button pressed page re-loads Multiply. aspx <html> <head> <title>Multiply</title> … </head> <body> <form action=Multiply. aspx method=post> … </form> </body> </html> Mark Dixon, So. CCE Page 13
Example: Multiply. aspx <html> <head> <title>Multiply</title> <% Dim tmp. Res Dim tmp. Num 1 Dim tmp. Num 2 do when button clicked Post to Self Mark Dixon, So. CCE If Request. Form("btn. Calc") <> "" Then tmp. Num 1 = CDbl(Request. Form("txt. Num 1")) tmp. Num 2 = CDbl(Request. Form("txt. Num 2")) tmp. Res = tmp. Num 1 * tmp. Num 2 End If %> </head> <body> <form name="frm. Default" action=Multiply. aspx method=post> <p><input name=txt. Num 1 type=text size=5 maxlength=5 value=<%=tmp. N <input name=txt. Num 2 type=text size=5 maxlength=5 value=<%=tmp. Nu <p><input name=btn. Calc type=submit value=Calc> </form> <p><%=tmp. Res%> </body> </html> Page 14
Maintaining State: Query Strings • Data added to end of URL (address): http: //localhost/page. asp? Surname=Bob Query String • ASP code can use this data: – Request. Query. String("Surname") • would return the value "Bob" • Form method=get – data automatically added to query string Mark Dixon, So. CCE Page 15
Example: Date-Time Menu. aspx <html> <head> </head> <body> <p>What background colour do you want for you date information? <a href=Date. Time. aspx? Colour=yellow>Yellow</a> <a href=Date. Time. aspx? Colour=cyan>Light Blue</a> </body> </html> Date. Time. aspx <html> <head> </head> <body bgcolor=<%=request. querystring("Colour")%>> <p>The date is <%=Format(Now(), "D")%>. <p>The time is <%=Format(Now(), "T")%>. </body> </html> Mark Dixon, So. CCE Page 16
Reference: Server Object Model • Request object: calling web page – Form: used to get form data from page – Query. String: used to get data from address (? ) • Response object: web page sent back – Write: used to put text into web page – Redirect: used to navigate to other page – Clear: erases all HTML in web page • Session object: store data between pages – Abandon: clears session data Mark Dixon, So. CCE Page 17
Example: Apples SPECIFICATION • User Requirements – help children learn numbers 1 - 10 • Software Requirements – Functional: – display random number of apples (between 1 & 10) – ask child how many apples are there – child enters answer – computer responds appropriately – Non-functional should be easy to use, and interesting Mark Dixon, So. CCE Page 18
Tutorial Exercises • LEARNING OBJECTIVE: pass data between pages using session variables, query strings, and self-posting • Task 1: Get Logon v 3 working (from the lecture) • Task 2: Get the Multiply example (from the lecture) working • Task 3: Get the Date-Time example (from the lecture) working • Task 4: Design and code the Apples example Mark Dixon, So. CCE Page 19
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