Mark Dixon Page 1 24 – Object Oriented Programming in ASP

Mark Dixon Page 2 Questions: HTML in VB Are these correct (assume variables and fields exist)? s = s + + rs.Fields("Model").value s = s rs.Fields("Length").value h = " " + h + " "  

Mark Dixon Page 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)  

Mark Dixon Page 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"

Mark Dixon Page 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

Mark Dixon Page 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

Mark Dixon Page 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

Mark Dixon Page 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

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

Mark Dixon Page 10 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 Implementing Class Diagrams Module Code: String Title: String GetTitle(): string SetTitle(t: string) Count(): integer

Mark Dixon Page 11 Public and Private Control access to properties and methods Class a Public x As Single Private y As Single End Class Dim b As New a b.x = 5 b.y = 10 this works (x is public)  this will fail (y is private)

Mark Dixon Page 12 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

Mark Dixon Page 13 Example: Counter (html) Counter

Mark Dixon Page 14 Example: Counter (code) 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 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 Counter.vb

Mark Dixon Page 15 Questions: OOP How many –classes –properties –methods –functions –procedures 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

Mark Dixon Page 16 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.