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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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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

  • Are these correct (assume variables and fields exist)?

    id = 4

    sql = SELECT * FROM Customer

    sql = sql " WHERE [CustID] = " + id + ";"

    rs.Open(sql, cs)


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"


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


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


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


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


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


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


Example: Animals


Example: Student


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)


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


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>


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


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


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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