Factory Pattern in VB.Net

A Simple Factory Pattern returns an instance of one of the several classes depending upon the parameters passed to the shared/non-shared factory method.

Typically, all these classes are inherited from a common parent class. Each of them has common methods. But each of them has their own optimization task operation on data.  

The following code implements the Simple Factory Pattern for the School Login System.

This application allows multi-access level user to login into the school system. Depending upon their userid/password they will be instantiated. 

SchoolPrincipal and SchoolTeacher are the classes derived from the SchoolUser base class. There is a UserFactory class which is responsible to instantiate the appropriate class instance (SchoolPrincipal or SchoolTeacher) depending upon the userid/password passed to its shared method GetSchoolUser. 

This method is entirely responsible for returning the appropriate class instance no matter how complex logic is involved. 

Diagram:

            

Base Class: 

Public Class SchoolUser
Public _Fname As String
Public _Lname As String
Public _UserType As String

Sub New()
End Sub
End Class

Derived Classes:           

1. This class is for School Principal

Public Class SchoolPrincipal Inherits SchoolUser

Sub New()
_Fname = "David "
_Lname = "Smith "
_UserType = "Principal"
End Sub
End Class

2. This class is for SchoolTeacher

Public Class SchoolTeacher Inherits SchoolUser

Sub New()
_Fname = "Patrecia"
_Lname = "Terry"
_UserType = "Teacher"
End Sub
End Class

Factory Class: 

Public Class UserFactory

Shared Function GetSchoolUser(ByVal _login As String,_ByVal _paswrd As String) As SchoolUser 
If _login = "principal" And _paswrd = "principal" Then
Return New SchoolPrincipal
ElseIf _login = "teacher" And _paswrd = "teacher" Then
Return New SchoolTeacher
Else
Throw New Exception
End If
End Function
End Class

Client application using the factory: 

Private Sub Button1_Click(ByVal sender As System.Object,_ByVal e As System.EventArgs) HandlesButton1.Click
Dim m_OUser As SchoolUser = UserFactory.GetSchoolUser(TextBox1.Text, TextBox2.Text)
MsgBox("User Type: " & m_OUser._UserType & vbNewLine & "Name: " & m_OUser._Fname & " " & m_OUser._Lname)
End Sub

Steps to run the project:

1. Unzip the SimpleFActory.zip

2. Build the solution.

3. Run the application. 

Enjoy!!