VB.Net Tutorial/Development/Exception

Basics of Visual Basic exception handling

Public Class Tester
    Public Shared Sub Main
    
      Try
         Dim numerator As Integer = Convert.ToInt32("123")
         Dim denominator As Integer = Convert.ToInt32("321")
         Dim result As Integer = numerator \ denominator
         Console.WriteLine(result)
      Catch formattingException As FormatException
         Console.WriteLine("You must enter two integers")
      Catch dividingException As DivideByZeroException
         Console.WriteLine(dividingException.Message)
      End Try
    End Sub
End Class

0

Catch Exception in a function

Module Module1
    Sub Main()
            Try
                AddNumbers(1, 2)
            Catch Except As Exception
                Console.WriteLine("Call generated error: " & Except.Message)
            End Try
    End Sub
    Function AddNumbers(ByVal A As Integer, ByVal B As Integer) As Integer
        Try
            Throw New ArithmeticException()
        Catch Except As Exception
            Console.WriteLine(Except.Message)
        End Try
    End Function
End Module

Overflow or underflow in the arithmetic operation.

Convert Exception to String

Module Module1
    Sub Main()
        Dim A, B, C As Integer
        A = 3
        B = 0
        Try
            C = A Mod B
        Catch Except As Exception
            Console.WriteLine(Except.ToString())
        End Try

    End Sub
End Module

System.DivideByZeroException: Attempted to divide by zero.
   at Module1.Main()

Display Exception Trace

Module Module1
    Sub Main()
        Try
            Console.WriteLine("Result: ", First())
        Catch Except As Exception
            Console.WriteLine(Except.StackTrace)
        End Try
    End Sub
    Private Function First() As Integer
        First = Second()
    End Function
    Private Function Second() As Integer
        Second = Third()
    End Function
    Private Function Third() As Integer
        Dim A As Integer = 0
        Third = 100 Mod A
    End Function
End Module

at Module1.Main()

Exception fields

Imports System.IO
Module Module1
    Sub Main()
        Dim SourceFile As StreamReader
        Try
            SourceFile = New StreamReader("FilenameISBad.XXX")
        Catch Except As Exception
            Console.WriteLine(Except.Message)
            Console.WriteLine(Except.Source)
            Console.WriteLine(Except.StackTrace)
            Console.WriteLine(Except.TargetSite.Name)
        End Try
    End Sub
End Module

Get Message from Exception

Module Module1
    Sub Main()
        Dim A, B, C As Integer
        A = 3
        B = 0
        Try
            C = A Mod B
        Catch Except As Exception
            Console.WriteLine(Except.Message())
        End Try
    End Sub
End Module

Attempted to divide by zero.

Serializable Exception Inheriting NullReferenceException

Imports System
Imports System.Runtime.Serialization
    <Serializable()> Public Class NodeNotFoundException : Inherits NullReferenceException
        Dim st As String()
        "Constructors
        Public Sub New()
            MyBase.New("No such node found in your collection.")
        End Sub
        Public Sub New(ByVal message As String)
            MyBase.New(message)
        End Sub
        Public Sub New(ByVal message As String, ByVal inner As Exception)
            MyBase.New(message, inner)
        End Sub
    End Class

Set Exception HelpLink

Option Strict On
 Imports System
 Class Tester
     Public Shared Function DoDivide(ByVal a As Double, ByVal b As Double) As Double
         If b = 0 Then
             Dim e As New System.DivideByZeroException( )
          e.HelpLink = "http://www.vbex.ru"
             Throw e
         End If
         If a = 0 Then
             Throw New System.ArithmeticException( )
         End If
         Return a / b
     End Function "DoDivide
     Shared Sub Main( )
         Try
             Dim a As Double = 5
             Dim b As Double = 0
             Console.WriteLine("{0} / {1} = {2}", a, b, DoDivide(a, b))
         Catch e As System.DivideByZeroException
             Console.WriteLine("DivideByZeroException! Msg: {0}", e.Message)
             Console.WriteLine("Helplink: {0}", e.HelpLink)
             Console.WriteLine("Stack trace: {0}", e.StackTrace)
         Catch
             Console.WriteLine("Unknown exception caught!")
         Finally
             Console.WriteLine("Close file here.")
         End Try
     End Sub "Main
 End Class "Tester

DivideByZeroException! Msg: Attempted to divide by zero.
Helplink: http://www.vbex.ru
Stack trace:    at Tester.DoDivide(Double a, Double b)
   at Tester.Main()
Close file here.

Throw Exception out of a Method

Option Strict On
 Imports System
 Class Tester
     Shared Sub Main( )
         Console.WriteLine("Enter Main...")
         Console.WriteLine("Enter Run...")
         Func1( )
         Console.WriteLine("Exit Run...")
         Console.WriteLine("Exit Main...")
     End Sub
     Public Shared Sub Func1( )
         Console.WriteLine("Enter Func1...")
         Func2( )
         Console.WriteLine("Exit Func1...")
     End Sub
     
     Public Shared Sub Func2( )
         Console.WriteLine("Enter Func2...")
         Throw New System.Exception( )
         Console.WriteLine("Exit Func2...")
     End Sub
 End Class

Enter Main...
Enter Run...
Enter Func1...
Enter Func2...
Unhandled Exception: System.Exception: Exception of type "System.Exception" was thrown.
   at Tester.Func2()
   at Tester.Main()

Use properties Message, StackTrace and InnerException

Class Tester
   Shared Sub Main()
      Try
         Method1()
      Catch exceptionParameter As Exception
         Console.WriteLine(exceptionParameter.ToString())
         Console.WriteLine(exceptionParameter.Message)
         Console.WriteLine(exceptionParameter.StackTrace)
         Console.WriteLine(exceptionParameter.InnerException.ToString())
      End Try
   End Sub 
   Public Shared Sub Method1()
      Method2()
   End Sub
   Public Shared Sub Method2()
      Method3()
   End Sub
   Public Shared Sub Method3()
      Try
         Convert.ToInt32("Not an integer")
      Catch formatException As FormatException
         Throw New Exception("Exception occurred in Method3", _
            formatException)
      End Try
   End Sub
End Class

System.Exception: Exception occurred in Method3 ---> System.FormatException: Input string was not in
 a correct format.
   at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFor
matInfo info, Boolean parseDecimal)
   at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info)
   at Tester.Method3()
   --- End of inner exception stack trace ---
   at Tester.Method3()
   at Tester.Main()
Exception occurred in Method3
   at Tester.Method3()
   at Tester.Main()
System.FormatException: Input string was not in a correct format.
   at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFor
matInfo info, Boolean parseDecimal)
   at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info)
   at Tester.Method3()