1. VB Classes
ISYS 512

2. Adding a Class to a Project
Project/Add Class
*** MyClass is a VB keyword.
Steps:
Adding properties
Declare Public variables in the General Declaration section
Property procedures: Set / Get
Adding methods
Adding events, exceptions

3. Anatomy of a Class Module
Exposed Part
Hidden Part
Public Variables &
Property Procedures
Private Variables
Public Procedures
& Functions
Private Procedures
& Functions
Private variables and procedures can be created for internal use.
Encapsulation

4. Class Code Example Public Eid As String Public Ename As String
Public salary As Double
Public Function tax() As Double
tax = salary * 0.1
End Function

5. Using a Class Define a class variable using New
Example: Dim MyEmp As New Emp

6. Creating Property with Property Procedures
Implementing a property with a public variable the property value cannot be validated by the class.
We can create read-only, write-only, or write-once properties with property procedure.
Steps:
Declaring a private class variable to hold the property value.
Writing a property procedure to provide the interface to the property value.

7. Private pvEid As String
Private pvEname As String
Private pvSalary As Double
Public Property eid() As String
Get
eid = pvEid
End Get
Set(ByVal Value As String)
pvEid = Value
End Set
End Property
Public Property eName() As String
eName = pvEname
pvEname = Value
Public Property Salary() As Double
Salary = pvSalary
Set(ByVal Value As Double)
pvSalary = Value

8. Property Procedure Code Example
Public Class Emp2
Public SSN As String
Public Ename As String
Public DateHired As Date
Private hiddenJobCode As Long
Public Property JobCode()
Set(ByVal Value)
If Value < 1 Or Value > 4 Then
hiddenJobCode = 1
Else
hiddenJobCode = Value
End If
End Set
Get
JobCode = hiddenJobCode
End Get
End Property
End Class

9. How the Property Procedure Works?
When the program sets the property, the property procedure is called and the code between the Set and End Set statements is executed. The value assigned to the property is passed in the Value argument and is assigned to the hidden private variable.
When the program reads the property, the property procedure is called and the code between the Get and End Get statements is executed.

10. Implementing a Read-Only Property
Declare the property procedure as ReadOnly with only the Get block.
Ex. Create a YearsEmployed property from the DateHired property:
Public ReadOnly Property YearsEmployed() As Long
Get
YearsEmployed = Now.Year - DateHired.Year
End Get
End Property
Note: It is similar to a calculated field in database.

11. Overloading
A class may have more than one methods with the same name but a different argument list (with a different number of parameters or with parameters of different data type), different parameter signature.

12. Method Overloading Using the Overloads Keyword
Public Overloads Function tax() As Double
tax = salary * 0.1
End Function
Public Overloads Function tax(ByVal sal As Double) As Double
tax = sal * 0.1

13. Inheritance
The process in which a new class can be based on an existing class, and will inherit that class’s interface and behaviors. The original class is known as the base class, super class, or parent class. The inherited class is called a subclass, a derived class, or a child class.

14. Employee Super Class with Three SubClasses
All employee subtypes will have emp nbr, name, address, and date-hired
Each employee subtype will also have its own attributes

15. Inheritance Example Public Class Emp Public Eid As String
Public Ename As String
Public salary As Double
Public Function tax() As Double
tax = salary * 0.1
End Function
End Class
Public Class secretary
Inherits Emp
Public WordsPerMinute As Integer

16. Database Handling Classes
ADO.Net
Objects
Database
Classes
Data Source
Forms
Reports

17. Single-Record-Handling Classes
Retrieves a single record from the database and makes it available to your application in the form of an object.
The fields in the record are exposed as the object’s properties.
Any actions performed by the data (updates, calculations, etc.) are exposed as the object’s methods.

18. Single-Record-Handling Class Example
Imports System.Data.OleDb
Public Class Customer
Public cid As String
Public CName As String
Public City As String
Public Rating As String
Private hiddenexist As Boolean
Private cn As OleDb.OleDbConnection
Public ReadOnly Property RecExist() As Boolean
Get
RecExist = hiddenexist
End Get
End Property

19. Dim objConn As New OleDbConnection(strConn)
Public Sub getData(ByVal SearchID As String)
Dim strConn As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\SalesDB2007.accdb"
Dim objConn As New OleDbConnection(strConn)
Dim strSQL As String = "select * from customer where cid = '" & SearchID & "'"
Dim objComm As New OleDbCommand(strSQL, objConn)
objConn.Open()
Dim objDataReader As OleDbDataReader
objDataReader = objComm.ExecuteReader()
If objDataReader.Read() = False Then
hiddenexist = False
Else
hiddenexist = True
cid = objDataReader("cid")
CName = objDataReader("CName")
City = objDataReader("City")
Rating = objDataReader("Rating")
End If
objConn.Close()
End Sub

20. Public Sub SaveNew()
Dim strConn As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\SalesDB2007.accdb"
Dim objConn As New OleDbConnection(strConn)
objConn.Open()
Dim strSQLInsert As String
strSQLInsert = "Insert into Customer values ('"
strSQLInsert = strSQLInsert & cid & "','" & CName & "','"
strSQLInsert = strSQLInsert & City & "','" & Rating & "')"
Dim objCommInsert As New OleDbCommand(strSQLInsert, objConn)
objCommInsert.ExecuteNonQuery()
objConn.Close()
End Sub

21. Using the SaveNew Method to Add A New Customer
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim newCust As New Customer()
newCust.cid = TextBox1.Text
newCust.CName = TextBox2.Text
newCust.City = TextBox3.Text
newCust.Rating = TextBox4.Text
newCust.SaveNew()
TextBox1.Text = ""
TextBox2.Text = ""
TextBox3.Text = ""
TextBox4.Text = ""
End Sub

22. Modeling 1:M Relation with Classes
Employee
EID
Ename
Dependents
Department
DID
Dname
Employees
Customer
CID
Cname
Orders

23. ArrayList ArrayList is a data structure used to store a set of values.
Its capacity is automatically expanded as needed.
Values stored in an arraylist do not have to be the same data type.
Flexibility when inserting/deleting elements.

24. ArrayList Properties & Methods
Define an arraylist:
Dim myArrayList As New ArrayList()
Properties:Count, Item, etc.
myArrayList.Item(0) 0-based index
Methods:
Clear, Add, Insert, Remove, RemoveAt, Contains, IndexOf, etc.

25. ArrayList Demo
Dim testArrayList As New ArrayList()
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim f2 As New Form2()
testArrayList.Add("David")
testArrayList.Add(20)
TextBox1.Text = testArrayList.Item(0)
TextBox2.Text = testArrayList.Item(1).ToString
End Sub

26. For Each Loop with ArrayList
Dim testArrayList As New ArrayList()
testArrayList.Add("David")
testArrayList.Add(20)
testArrayList.Add(Fruits)
Dim myObj As Object
For Each myObj In testArrayList
MessageBox.Show(myObj.GetType.ToString)
Next

27. Implementing a 1:M Relationship With ArrayList
Class Customer
Public cid As String
Public cname As String
Public city As String
Public rating As String
Public orders As New ArrayList
Methods:
GetData
GetOrders
Class Order
Public OID As String
Public Odate As Date
Public SalesPerson As String

28. Customer Class Public Class Customer Public cid As String
Public cname As String
Public city As String
Public rating As String
Public orders As New ArrayList
Private hiddenexist As Boolean
Public Sub getData(ByVal SearchID As String)
Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\salesDB.mdb"
Dim objConn As New OleDbConnection(strConn)
Dim strSQL As String = "select * from customer where cid = '" & SearchID & "'"
Dim objComm As New OleDbCommand(strSQL, objConn)
objConn.Open()
Dim objDataReader As OleDbDataReader
objDataReader = objComm.ExecuteReader()
If objDataReader.Read() = False Then
hiddenexist = False
MessageBox.Show("Record does not exist")
Else
hiddenexist = True
cid = objDataReader("cid")
cname = objDataReader("CName")
city = objDataReader("City")
rating = objDataReader("Rating")
End If
objConn.Close()
End Sub

29. GetOrders Method Public Sub getOrders(ByVal SearchID As String)
Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\salesDB.mdb"
Dim objConn As New OleDbConnection(strConn)
Dim strSQL As String = "select * from orders where cid = '" & SearchID & "'"
Dim objComm As New OleDbCommand(strSQL, objConn)
objConn.Open()
Dim objDataReader As OleDbDataReader
objDataReader = objComm.ExecuteReader()
Do While objDataReader.Read() = True
Dim ord As New Order()
ord.oid = objDataReader("oid")
ord.CID = objDataReader("cid")
ord.Odate = objDataReader("odate")
ord.SalesPerson = objDataReader("salesPerson")
orders.Add(ord)
Loop
If orders.Count = 0 Then
MessageBox.Show("customer has no order")
End If
objConn.Close()
End Sub

30. Order Class Public Class Order Private pvOID As String
Private pvCID As String
Private pvOdate As Date
Private pvSalesPerson As String
Public Property OID() As String
Get
oid = pvOID
End Get
Set(ByVal value As String)
pvOID = value
End Set
End Property
Public Property CID() As String
CID = pvCID
pvCID = value
Public Property Odate() As Date
Odate = pvOdate
Set(ByVal value As Date)
pvOdate = value
Public Property Salesperson() As String
Salesperson = pvSalesPerson
pvSalesPerson = value
End Class

31. Binding Datagrid to an ArrayList
DataGridView1.DataSource = myCustomer.orders
Members of the arraylist are instances of same class.
The properties of the class are defined by property procedure.

32. Example

33. Code Example
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\salesDB.mdb"
Dim objConn As New OleDbConnection(strConn)
Dim strSQL As String = "select cid from customer;"
Dim objComm As New OleDbCommand(strSQL, objConn)
objConn.Open()
Dim objDataReader As OleDbDataReader
objDataReader = objComm.ExecuteReader()
Do While objDataReader.Read() = True
ListBox1.Items.Add(objDataReader("cid"))
Loop
objConn.Close()
End Sub
Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged
Dim myCustomer As New Customer
myCustomer.getData(ListBox1.SelectedItem)
TextBox1.Text = myCustomer.cname
TextBox2.Text = myCustomer.rating
myCustomer.getOrders(myCustomer.cid)
DataGridView1.DataSource = myCustomer.orders

34. Difference between Assembly and Class
A class defined in a project is available to that project only.
Once a class is compiled in an assembly it can be used by any projects.
To create an assembly:
Start a Class Library project

35. Steps to Create An Assembly
Start a Class Library project
Create classes
You can also use existing classes defined in other projects by Project/Add Existing Item
Save project
Select Build/Build to compile the code.
When the class library is compiled successfully, an assembly is created and stored in the project’s Bin/Release folder.
Example: A testClassLib project is created in C:\VS2008Examples, then the assembly is found in:
C:\VS2008Examples\testClassLib\testClassLib\bin\Release

36. Using the Assembly
Reference the assembly: Project/Add Reference and use the Browse button to select the assembly.
Import the assembly.
Global import:
Project property windows/References
Local import
Using the Imports statement

37. Code Using Assembly Imports MyClassDemo Public Class Form1
Dim myButton As New Button
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim myCls As New DemoCls1
MessageBox.Show(myCls.myName)
End Sub

38. Changes to Assembly
Old projects referencing the assembly will get the latest version of the assembly.
Compatible changes:
Changes to assembly that will not break the older projects.
Examples:
Adding a property, adding a method
Incompatible changes
Changes to assembly that will break the older projects.
Deleting or renaming a property or a method