VB.Net Tutorial/Development/Custom Exception

Create Custom Exception class

<source lang="vbnet">Option Strict On

Imports System
Public Class MyCustomException
    Inherits System.ApplicationException
    Public Sub New(ByVal message As String)
        MyBase.New(message)
    End Sub
End Class
Class Tester
    Public Shared Function DoDivide(ByVal a As Double, ByVal b As Double) As Double
        If b = 0 Then
            Dim e As New DivideByZeroException( )
            e.HelpLink = "http://www.vbex.ru"
            Throw e
        End If
        If a = 0 Then
            Dim e As New _
              MyCustomException("Can"t have zero divisor")
            e.HelpLink = "http://www.vbex.ru"
            Throw e
        End If
        Return a / b
    End Function "DoDivide
    Shared Sub Main( )
        Try
            Console.WriteLine("Open file here")
            Dim a As Double = 0
            Dim b As Double = 5
            Console.WriteLine("{0} / {1} = {2}", a, b, DoDivide(a, b))
            Console.WriteLine("This line may or may not print")
        Catch e As System.DivideByZeroException
            Console.WriteLine("DivideByZeroException! Msg: {0}", e.Message)
            Console.WriteLine("HelpLink: {0}", e.HelpLink)
        Catch e As MyCustomException
            Console.WriteLine("MyCustomException! Msg: {0}", e.Message)
            Console.WriteLine("HelpLink: {0}", e.HelpLink)
        Catch
            Console.WriteLine("Unknown exception caught")
        Finally
            Console.WriteLine("Close file here.")
        End Try
    End Sub
End Class</source>

Open file here
MyCustomException! Msg: Can"t have zero divisor
HelpLink: http://www.vbex.ru
Close file here.

Create your own Exception class by subclassing System.Exception

<source lang="vbnet">Imports System.Runtime.Serialization Public Class CustomException

  Inherits System.Exception
  Public Sub New()
     Me.New("An error occurred in the component.", Nothing)
  End Sub
  Public Sub New(message As String)
     Me.New(message, Nothing)
  End Sub
  Public Sub New(message As String, innerException As Exception)
     MyBase.New(message, innerException)
     Source = "My_Custom_Component"
  End Sub
  Protected Sub New(info As SerializationInfo, context As StreamingContext)
     MyBase.New(info, context)
  End Sub

End Class</source>

Demonstrating a user-defined exception class

<source lang="vbnet">Public Class Tester

   Public Shared Sub Main
   
     Try
        Console.WriteLine(SquareRoot(123.123))
        Console.WriteLine(SquareRoot(-123.123))
     Catch formatException As FormatException
        Console.WriteLine(formatException.Message)
     Catch negativeNumberException As _
        NegativeNumberException
        Console.WriteLine(negativeNumberException.Message)
     End Try
   End Sub
  Public Shared Function SquareRoot(ByVal operand As Double) As Double
     If operand < 0 Then
        Throw New NegativeNumberException( _
           "Square root of negative number not permitted")
     End If
     Return Math.Sqrt(operand)
  End Function " cmdSquareRoot

End Class

Public Class NegativeNumberException

  Inherits ApplicationException
  Public Sub New()
     MyBase.New("Illegal operation for a negative number")
  End Sub " New
  Public Sub New(ByVal messageValue As String)
     MyBase.New(messageValue)
  End Sub " New
  Public Sub New(ByVal messageValue As String, _
     ByVal inner As Exception)
     MyBase.New(messageValue, inner)
  End Sub

End Class</source>

11.0960803890383
Square root of negative number not permitted

Inherits System.ApplicationException

<source lang="vbnet">Imports System.Runtime.Serialization public class Test

  public Shared Sub Main
       Try
           Throw New MyException("This is my Exception.")
       Catch ex As Exception
           Console.WriteLine(ex.Message)
       End Try
  End Sub

End class

Public Class MyException

   Inherits System.ApplicationException
   Public Sub New()
       MyBase.New("This object has expired")
   End Sub
   Public Sub New(ByVal new_message As String)
       MyBase.New(new_message)
   End Sub
   Public Sub New(ByVal new_message As String, ByVal inner_exception As Exception)
       MyBase.New(new_message, inner_exception)
   End Sub
   Public Sub New(ByVal info As SerializationInfo, _
   ByVal context As StreamingContext)
       MyBase.New(info, context)
   End Sub

End Class</source>

This is my Exception.