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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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Questions html in vb
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
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
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
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
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
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
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
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
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




Public and private
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
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
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
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
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
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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