ExceptionHandlingClause Class
Assembly: mscorlib (in mscorlib.dll)
'Declaration <ComVisibleAttribute(True)> _ Public NotInheritable Class ExceptionHandlingClause 'Usage Dim instance As ExceptionHandlingClause
/** @attribute ComVisibleAttribute(true) */ public final class ExceptionHandlingClause
ComVisibleAttribute(true) public final class ExceptionHandlingClause
Not applicable.
The ExceptionHandlingClause class provides information about the clauses in a try…catch…finally block (Try…Catch…Finally in Visual Basic). To get a list of exception-handling clauses in a method, obtain a MethodInfo that represents the method. Use the GetMethodBody method to obtain a MethodBody object, and then use the ExceptionHandlingClauses property to get the list of clauses.
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| 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 at http://msdn.microsoft.com/net/ecma/ and http://www.ecma-international.org/publications/standards/Ecma-335.htm. |
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.
You can use Ildasm.exe to examine the MSIL for the compiled code example, to see how the offsets and lengths are calculated.
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| 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 located in the MethodBody class topic.
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
Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.
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