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ExceptionHandlingClauseOptions Enumeration

Identifies kinds of exception-handling clauses.

This enumeration has a FlagsAttribute attribute that allows a bitwise combination of its member values.

Namespace:  System.Reflection
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
<ComVisibleAttribute(True)> _
<FlagsAttribute> _
Public Enumeration ExceptionHandlingClauseOptions

Member nameDescription
ClauseThe clause accepts all exceptions that derive from a specified type.
FaultThe clause is executed if an exception occurs, but not on completion of normal control flow.
FilterThe clause contains user-specified instructions that determine whether the exception should be ignored (that is, whether normal execution should resume), be handled by the associated handler, or be passed on to the next clause.
FinallyThe clause is executed whenever the try block exits, whether through normal control flow or because of an unhandled exception.

To examine the exception-handling clauses in a method, obtain a MethodInfo object and call the GetMethodBody method to obtain the method body. Use the ExceptionHandlingClauses property to obtain a list of ExceptionHandlingClause objects.

NoteNote

Working with exception-handling clauses requires a thorough understanding of metadata and Microsoft intermediate language (MSIL) instruction formats. Information can be found in the Common Language Infrastructure (CLI) documentation, especially "Partition II: Metadata Definition and Semantics" and "Partition III: CIL Instruction Set". The documentation is available online; see ECMA C# and Common Language Infrastructure Standards on MSDN and Standard ECMA-335 - Common Language Infrastructure (CLI) on the Ecma International Web site.

The following code example defines a test method named MethodBodyExample, and displays its local variable information and exception-handling clauses. The MethodBase.GetMethodBody method is used to obtain a MethodBody object for the test method. The ExceptionHandlingClauses property is used to obtain a list of ExceptionHandlingClause objects and display their properties.

NoteNote

Not all computer languages can generate ExceptionHandlingClauseOptions.Filter clauses. The Visual Basic example shows a filter clause, using a Visual Basic When expression, which is omitted from the examples for other languages.

This code is part of a larger example provided for the MethodBody class.

Imports System
Imports System.Reflection

Public Class Example

    Public Shared Sub Main()

        ' Demonstrate the effect of the Visual Basic When keyword, which 
        ' generates a Filter clause in the Try block. 
        Dim e As New Example()
        Console.WriteLine()
        e.MethodBodyExample("String argument")
        e.MethodBodyExample(Nothing)

        ' Get method body information. 
        Dim mi As MethodInfo = _
            GetType(Example).GetMethod("MethodBodyExample")
        Dim mb As MethodBody = mi.GetMethodBody()
        Console.WriteLine(vbCrLf & "Method: {0}", mi)

        ' Display the general information included in the  
        ' MethodBody object.
        Console.WriteLine("    Local variables are initialized: {0}", _
            mb.InitLocals)
        Console.WriteLine("    Maximum number of items on the operand stack: {0}", _
            mb.MaxStackSize)


...



' Display exception handling clauses.
Console.WriteLine()
For Each ehc As ExceptionHandlingClause In mb.ExceptionHandlingClauses
    Console.WriteLine(ehc.Flags.ToString())

    ' The FilterOffset property is meaningful only for Filter 
    ' clauses. The CatchType property is not meaningful for  
    ' Filter or Finally clauses.  
    Select Case ehc.Flags
        Case ExceptionHandlingClauseOptions.Filter
            Console.WriteLine("        Filter Offset: {0}", _
                ehc.FilterOffset)
        Case ExceptionHandlingClauseOptions.Finally 
        Case Else
            Console.WriteLine("    Type of exception: {0}", _
                ehc.CatchType)
    End Select

    Console.WriteLine("       Handler Length: {0}", ehc.HandlerLength)
    Console.WriteLine("       Handler Offset: {0}", ehc.HandlerOffset)
    Console.WriteLine("     Try Block Length: {0}", ehc.TryLength)
    Console.WriteLine("     Try Block Offset: {0}", ehc.TryOffset)
Next


...


    End Sub 

    ' This test method is executed at the beginning of Main, to show 
    ' how the Filter clause works. The Filter clause is generated by  
    ' a Visual Basic When expression. If arg is Nothing, this method 
    ' throws ArgumentNullException, which is caught by the filter 
    ' clause. If arg is a string, the method throws ArgumentException, 
    ' which does not match the filter clause. 
    
    ' Sub Main also contains code to analyze this method, using  
    ' the properties and methods of the MethodBody class. 
    Public Sub MethodBodyExample(ByVal arg As Object)

        ' Define some local variables. In addition to these variables, 
        ' the local variable list includes the variables scoped to  
        ' the catch clauses. 
        Dim var1 As Integer = 42
        Dim var2 As String = "Forty-two" 

        Try 
            ' Depending on the input value, throw an ArgumentException or  
            ' an ArgumentNullException to test the Catch clauses. 
            
            If arg Is Nothing Then 
                Throw New ArgumentNullException("The argument cannot be Nothing.")
            End If 
            If arg.GetType() Is GetType(String) Then 
                Throw New ArgumentException("The argument cannot be a string.")
            End If 

        ' The When expression makes this a filter clause. The expression  
        ' selects only exceptions that derive from the ArgumentException 
        ' class. Other exceptions, including ArgumentException itself,  
        ' are not handled by this filter clause. 
        Catch ex As ArgumentException _
            When ex.GetType().IsSubclassOf(GetType(ArgumentException))

            Console.WriteLine("Filter clause caught: {0}", ex.GetType())

        ' This catch clause handles the ArgumentException class, and 
        ' any other class derived from Exception. 
        Catch ex As Exception
            Console.WriteLine("Ordinary exception-handling clause caught: {0}", _
                ex.GetType())

        Finally
            var1 = 3033
            var2 = "Another string." 
        End Try 
    End Sub 
End Class 

' This code example produces output similar to the following: 

'Ordinary exception-handling clause caught: System.ArgumentException 
'Filter clause caught: System.ArgumentNullException 

'Method: Void MethodBodyExample(System.Object) 
'    Local variables are initialized: True 
'    Maximum number of items on the operand stack: 3


...



'Filter 
'        Filter Offset: 0 
'       Handler Length: 19 
'       Handler Offset: 99 
'     Try Block Length: 45 
'     Try Block Offset: 9 
'Clause 
'    Type of exception: System.Exception 
'       Handler Length: 25 
'       Handler Offset: 118 
'     Try Block Length: 45 
'     Try Block Offset: 9 
'Finally 
'       Handler Length: 13 
'       Handler Offset: 153 
'     Try Block Length: 144 
'     Try Block Offset: 9

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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