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Mark Dixon 1 23 – Object Oriented Programming in ASP
Mark Dixon 1
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• 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
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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
– 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:
Module
Code: stringTitle: string
GetTitle(): stringSetTitle(t: string)Count(): integer
Class Attributes/Properties
Class Operations/Methods
Class Name
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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 IntegerEnd Class
Implementing Class Diagrams
Module
Code: StringTitle: String
GetTitle(): stringSetTitle(t: string)Count(): integer
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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 SubEnd 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)<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">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 IfEnd Sub</script>
Public 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 SubEnd Class
Counter.vb Must be in App_Code
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.NET Folders• Right click project
– App_Code – used for classes (put all classes here)– App_Data – used for databases
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Questions: OOP• How many
– classes
– properties
– methods
– functions
– procedures
Public 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 SubEnd Class
Function Twice(x As Long) As Long Return x * 2End Function
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.
