Partial Class in Dot Net with Examples

Defination :

Partial Class allows to split definition of classes, interfaces and structures over more than one files.The compilers for VB.Net or C# look for the partial classes and integrate them while compiling, to form the intermediate language. This intermediate language is the same when compared to the intermediate language that is generated, if all the partial classes are combined to form a single class in a single file. There is no modification done in the CLR for the implementation of partial classes.

This benefits of partial classes is "

1 - It allows a clean separation of business logic and the user interface
2 - It allows programmers to work simultaneously on different parts of a class without needing to share the same physical file.
3 - You can easily write your code for extended functionality for a VS.NET generated class. This will allow you to write the code of your own need without messing with the system generated code.


Code Example :

'Class 1 : To Define the Class, Class variables and Constructors

Imports Microsoft.VisualBasic

Public Class Calcuator

    Dim Param1 As New Decimal
    Dim param2 As New Decimal
    Dim strMsg As String

    Public Sub New()
        Param1 = 0
        param2 = 0
    End Sub

    Public Sub New(ByVal x As String, ByVal y As String)
        'fnCheckData : It uses the method defined in Partial Class 2
        If fnCheckData(x, y) Then
            Param1 = x
            param2 = y
        End If
    End Sub

End Class


'Class 2 : To Validate the value for Class variables 

Imports Microsoft.VisualBasic

Partial Public Class Calcuator

    Public Function fnCheckData(ByVal x As String, ByVal y As String) As Boolean
        If IsNumeric(x) And IsNumeric(y) Then
            fnCheckData = True
        End If
        Return fnCheckData
    End Function

End Class


'Class 3 : All the Business Logics are written here. 
'It uses the Class variables defined in Partial Class 1

Imports Microsoft.VisualBasic

Partial Public Class Calcuator

    Public Function Add() As Decimal
        Add = Param1 + param2
        Return Add
    End Function

    Public Function SubStract() As Decimal
        SubStract = Param1 - param2
        Return SubStract
    End Function

    Public Function Division() As Decimal
        If param2 <> 0 Then
            Division = Param1 / param2
        End If
        Return Division
    End Function

    Public Function Multiplication() As Decimal
        Multiplication = Param1 * param2
        Return Multiplication
    End Function

End Class


'Form : Where Partial Class Implemented

Partial Class Default5
    Inherits System.Web.UI.Page

    'Create the partial class object. It Uses Partial Class 1
    Dim calc As New Calcuator()

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        'Reintialise the partial class object. It Uses Partial Class 1
        calc = New Calcuator(TextBox1.Text, TextBox2.Text)
    End Sub

    'Implement the partial class Methods for the Respective Button Click. It Uses Partial Class 3
    Protected Sub btnAdd_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnAdd.Click
        lblResult.Text = calc.Add()
    End Sub

    Protected Sub btnSub_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnSub.Click
        lblResult.Text = calc.SubStract()
    End Sub

    Protected Sub btnMul_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnMul.Click
        lblResult.Text = calc.Multiplication()
    End Sub

    Protected Sub btnDiv_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnDiv.Click
        lblResult.Text = calc.Division()
    End Sub

End Class