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23 – Object Oriented Programming in ASP

23 – Object Oriented Programming in ASP. Questions: HTML in VB. Are these correct (assume variables and fields exist)? s = s + <td> + rs.Fields(" Model ").value s = s rs.Fields(" Length ").value h = "< div >" + h + "</ div >". . . . Questions: SQL in VB.

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23 – Object Oriented Programming in ASP

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  1. 23 – Object Oriented Programming in ASP

  2. Questions: HTML in VB • Are these correct (assume variables and fields exist)? s = s + <td> + rs.Fields("Model").value s = s rs.Fields("Length").value h = "<div>" + h + "</div>"   

  3. Questions: SQL in VB • Are these correct (assume variables and fields exist)? id = 4 sql = SELECT * FROM Customer sql = sql " WHERE [CustID] = " + id + ";" rs.Open(sql, cs)    

  4. Questions: Writing to Databases • Write a line of VB code to add a new record to a recordset called rs. • Write a line of VB code to remove the current record from a recordset called rs. • Write a line of VB code to put "Hello" into a field called Message in the current record rs.AddNew() rs.Delete() rs.Fields("Message").Value = "Hello"

  5. Session Aims & Objectives • Aims • To highlight that the object oriented techniques covered earlier can be used in ASP • Objectives,by end of this week’s sessions, you should be able to: • create a class definition in server-side code • create an instance of a class • create a class definition from a class diagram

  6. Object-Oriented Paradigm • A program is made up of a number of objects that communicate with each other by passing messages • Each object contains • attributes/properties that represent its state, and • operations/methods that represent its behaviour • Objects often mirror the real world • Customers • Students • Patients

  7. Classes and Instances • Object Classes • general descriptions of types of objects,e.g. student, product, customer, lecturer, and room. • Object Instances • specific items of a given class, e.g. • each of you could be an instance of the student class • Room 214 could be an instance of the room class • I could be an instance of the lecturer class • Bolt could be an instance of the part class

  8. Object Concepts - Implementation • Properties – implemented as • data structures (variables, arrays, and types). • Methods – implemented as either • a procedure (to perform some processing), or • a function (to return a value). • Object oriented paradigm builds on (rather than replaces) the structured paradigm

  9. Class Diagrams • Used to describe structure of object classes: Class Name Module Code: string Title: string Class Attributes/Properties GetTitle(): string SetTitle(t: string) Count(): integer Class Operations/Methods

  10. Implementing Class Diagrams Module Code: String Title: String GetTitle(): string SetTitle(t: string) Count(): integer Class Module Public Code As String Public Title As String Public Function GetTitle() As String Public Sub SetTitle(t As String) Public Function Count() As Integer End Class

  11. Example: Animals

  12. Example: Student

  13. Public and Private • Control access to properties and methodsClass a Public x As Single Private y As Single Public Sub ResetY() y = 0 End SubEnd ClassDim b As New a b.x = 5 b.ResetY() b.y = 10  this works (x is public) this works (ResetY is public) this will fail (y is private)

  14. Benefits of OOP in code • Procedures and Functions are part of object • encapsulation • RelatedData and Operationstogether • Private keyword – restrict access to data • Clearer code • Less prone to error

  15. Example: Counter (html) <html> <head><title>Counter</title></head> <body> <form runat="server"> <input id="btnReset" type="submit" value="Reset" runat="server" /> <input id="btnUp" type="submit" value="Up" runat="server" /> <input id="btnDown" type="submit" value="Down" runat="server" /> <p id="parMsg" runat="server"></p> </form> </body> </html>

  16. Example: Counter (code) <script language="VB" runat="server" src="Counter.vb"></script> <script language="VB" runat="server"> Dim c As Object Sub Page_Load() If Session("c") Is Nothing Then Session("c") = New Counter Else c = Session("c") If Request.Form("btnReset") > "" Then c.Reset() ElseIf Request.Form("btnUp") > "" Then c.Up() ElseIf Request.Form("btnDown") > "" Then c.Down() End If parMsg.innerText = c.GetCount() End If End Sub </script> Counter.vb Class Counter Private mCount As Long Public Function GetCount() As Long GetCount = mCount End Function Public Sub Reset() mCount = 0 End Sub Public Sub Up() mCount = mCount + 1 End Sub Public Sub Down() mCount = mCount - 1 End Sub End Class

  17. Questions: OOP Class Counter Private mCount As Long Public Function GetCount() As Long GetCount = mCount End Function Public Sub Reset() mCount = 0 End Sub Public Sub Up() mCount = mCount + 1 End Sub Public Sub Down() mCount = mCount - 1 End Sub End Class Function Twice(x As Long) As Long Return x * 2 End Function • How many • classes • properties • methods • functions • procedures 1 1 4 2 3

  18. Tutorial Exercise: Counter • Task 1: Get the Counter example from the lecture working. • Task 2: Modify your code – so that the value cannot go below 0 or above 10.

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