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16 – Passing Data between pages: Forms, Sessions, & Query Strings

16 – Passing Data between pages: Forms, Sessions, & Query Strings. 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

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16 – Passing Data between pages: Forms, Sessions, & Query Strings

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  1. 16 – Passing Data between pages:Forms, Sessions, & Query Strings

  2. 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

  3. Example: Logon v2 (design) • Restrict access tohome page

  4. Example: Logon v2 (code) Home.htm <html> <head><title>My Home page</title></head> <body> <p> Welcome to my home page.<br /> <img src="YouAreHere.jpg" /> </p> </body> </html> Logon.aspx <script language="VB" runat="server"> Sub Page_Load() Dim un As String Dim pw As String If Request.Form("btnLogon") > "" Then un = txtUserName.Value pw = txtPassWord.Value If un = "mark" And pw = "soft131" Then Response.Redirect("home.htm") Else msg.innerText = "Login details incorrect." End If End If End Sub </script> <html> <head><title></title></head> <body> <form runat="server"> Please logon:<br /> <input id="txtUserName" type="text" runat="server" /><br /> <input id="txtPassWord" type="text" runat="server" /><br /> <input id="btnLogon" type="submit" value="Logon" runat="server" /> <p id="msg" runat="server"></p> </form> </body> </html>

  5. Example: Logon (Fixed Problem) • View Source – shows client-side script: No server-side code

  6. Example: Logon (Problem 2) • User can type home page url (address) directly (bypassing logon page)

  7. Solution • Need way for: • password page to tell home page • that user logged in OK

  8. Technique: Dead-Drop Variables • 2 Spies wish to pass message between each other without actually meeting • Arrange a dead-drop location • one spy leaves message at location • other spy visits location later to pick up message • Variables used as dead-drop containers

  9. Example: Logon v3 (code) Home3.aspx <script runat="server" language="VB"> Dim LogonOK As Boolean Sub Page_Load() If LogonOK = False Then Response.Redirect("Logon3.aspx") End If End Sub </script> <html> <head><title>My Home page</title></head> <body> <p> Welcome to my home page.<br /> <img src="YouAreHere.jpg" /> </p> </body> </html> Logon3.aspx <script language="VB" runat="server"> Dim LogonOK As Boolean Sub Page_Load() Dim un As String Dim pw As String LogonOK = False If Request.Form("btnLogon") > "" Then un = txtUserName.Value pw = txtPassWord.Value If un = "mark" And pw = "soft131" Then LogonOK = True Response.Redirect("home3.htm") Else msg.innerText = "Login details incorrect." End If End If End Sub </script> <html> <head><title></title></head> <body> <form runat="server"> Please logon:<br /> <input id="txtUserName" type="text" runat="server" /><br /> <input id="txtPassWord" type="text" runat="server" /><br /> <input id="btnLogon" type="submit" value="Logon" runat="server" /> <p id="msg" runat="server"></p> </form> </body> </html> • Error: always redirect to logon LogonOK True

  10. Example: Logon v3 (Error) • Variables – don't persist between pages

  11. Passing Data (temporary) • Session object • used to pass information between pages: • exists for current session • persist between pages • clears if user closes browser • clears after 20 mins of inactivity • no need for declaration Session("Thing") = 91 Put 91 into Thing

  12. Maintaining State: Session Object Send.aspx <script runat="server" language="VB"> Sub Page_Load() If Request.Form("btnSend") > "" Then Session("MSG") = "Meet in BGB202" ElseIf Request.Form("btnClear") > "" Then Session.Abandon() End If End Sub </script> <html> <head><title></title></head> <body> <form runat="server"> <input id="btnSend" type="submit" value="Send" runat="server" /> <input id="btnClear" type="submit" value="Clear" runat="server" /> <p><a href="Display.aspx">Display</a></p> </form> </body> </html> • Session variable • all strings • no declaration • Abandon method • deletes all session variables

  13. Maintaining State: Session Object Display.aspx <script runat="server" language="VB"> Sub Page_Load() parMsg.InnerText = Session("MSG") End Sub </script> <html> <head><title></title></head> <body> <p id="parMsg" runat="server"></p> </body> </html> • read session variable, and display in parMsg

  14. Example: Message Display.aspx <script runat="server" language="VB"> Sub Page_Load() parMsg.InnerText = Session("MSG") End Sub </script> <html> <head><title></title></head> <body> <p id="parMsg" runat="server"></p> </body> </html> Send.aspx <script runat="server" language="VB"> Sub Page_Load() If Request.Form("btnSend") > "" Then Session("MSG") = "Meet in BGB202" ElseIf Request.Form("btnClear") > "" Then Session.Abandon() End If End Sub </script> <html> <head><title></title></head> <body> <form runat="server"> <input id="btnSend" type="submit" value="Send" runat="server" /> <input id="btnClear" type="submit" value="Clear" runat="server" /> <p><a href="Display.aspx">Display</a></p> </form> </body> </html> • Using Session variable: MSG Meet in BGB202

  15. Questions: Session Variables • Write a line of VB code to put the number 74 into a session variable called id. • Write VB code that displays 'Hello' in parMsg if the session variable called id is equal to 74 Session("id") = 74 If Session("id") = 74 Then parMsg.InnerText = "Hello" End If

  16. Example: Apples (analysis) • 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-functionalshould be easy to use, and interesting

  17. Example: Apples (code) Apples.aspx Dim n As Long Sub Page_Load() Dim html As String Dim a As Long If Request.Form("btnStart") > "" Then n = 1 + Int(Rnd() * 9) html = "How many apples are there?<br />" For a = 1 To n html = html & "<img src=Apple.gif>" Next quest.InnerHtml = html ElseIf Request.Form("btnCheck") > "" Then If CInt(txtAns.Value) = CInt(n) Then msg.InnerHtml = "Correct, well done!" Else msg.InnerHtml = "Sorry, please try again." End If End If End Sub • What will this do?

  18. Passing Data (temporary) • Query Strings • Useful for passing information between pages via links

  19. Maintaining State: Query Strings Query String • Data added to end of URL (address):http://localhost/page.asp?Surname=Bob • ASP code can use this data: • Request.QueryString("Surname") • would return the value "Bob" • Form method=get • data automatically added to query string

  20. Example: Date-Time Menu.aspx <html> <head> </head> <body> <p>What background colour do you want for you date information? <br><a href=DateTime.aspx?Colour=yellow>Yellow</a> <br><a href=DateTime.aspx?Colour=cyan>Light Blue</a> </body> </html> DateTime.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>

  21. Reference: Server Object Model • Request object: calling web page • Form: used to get form data from page • QueryString: 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

  22. Passing Data (persistent) • Cookies (not covered in this module) • stored on users’ (client) hard drive • persists between sessions • Database/file (covered in later lectures) • stored on server hard drive • persists between sessions

  23. Tutorial Exercise: Message • LEARNING OBJECTIVE:pass data between pages using session variables, and (form)self-posting • Task 1: Get the message example working (from the lecture) • Task 2: Change the send.aspx page so that when you click the buttons it gives some feedback as to what has happened. hint: add a paragraph

  24. Tutorial Exercise: Apples • LEARNING OBJECTIVE:pass data between pages using session variables, and (form)self-posting • Task 1: Type in the code for the Apples example (from the lecture) • Task 2: Modify this to use a session variable to 'remember' the random number, so that it works. • Task 3: Change it so that it disables the buttons appropriately • Task 4: Change it so that it clears the text box and feedback as a new question begins

  25. Tutorial Exercise: Logon • LEARNING OBJECTIVE:pass data between pages using session variables, and (form)self-posting • Task 1: Type in the code for the Logon v3 example (from the lecture) NOTE: this will not work properly (variables do not persist between pages) • Task 2: Modify this to use a session variable to 'remember' whether the logon was successful. Note: It should not be possible to view the source code Note: It should not be possible to bypass the logon

  26. Tutorial Exercise: Date • LEARNING OBJECTIVE:pass data between pages using query strings • Task 1: Get the Date-Time example (from the lecture) working • Task 2: Modify your page to provide another choice of background colour.

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