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23 – Object Oriented Programming in ASP
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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>"
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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)
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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"
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Session Aims & Objectives
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
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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
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Classes and Instances Object Classes Object Instances
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
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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
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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
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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
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Example: Animals
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Example: Student
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Public and Private Control access to properties and methods Class a Public x As Single Private y As Single Public Sub ResetY() y = 0 End Sub End Class Dim 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)
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Benefits of OOP in code Procedures and Functions are part of object
encapsulation Related Data and Operations together Private keyword – restrict access to data Clearer code Less prone to error
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Example: Counter (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>
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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 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 Public Sub Down() mCount = mCount - 1 End Class
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Questions: OOP 1 1 4 2 3 How many classes properties methods functions
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 Public Sub Down() mCount = mCount - 1 End Class Function Twice(x As Long) As Long Return x * 2 How many classes properties methods functions procedures 1 1 4 2 3
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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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