MethodBody Class
Assembly: mscorlib (in mscorlib.dll)
The MethodBody class provides access to information about the local variables and exception-handling clauses in a method body, and to the Microsoft intermediate language (MSIL) that makes up the method body.
You can use the token-resolution methods of the module class, such as ResolveType, ResolveMethod, and ResolveType, to resolve the tokens in the method body to Type objects, MethodInfo objects, and FieldInfo objects that provide detailed information about the types, methods, and fields accessed by the MSIL in the method body.
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| Parsing method bodies requires a thorough understanding of metadata and 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. |
To obtain a MethodBody object for a given method, first obtain a MethodInfo object for the method, then call the MethodInfo object's GetMethodBody method.
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 example uses the LocalVariables property to obtain a list of LocalVariableInfo objects and then displays their types and index order. The ExceptionHandlingClauses property is used to obtain a list of exception-handling clauses.
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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. |
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 information about the local variables in the ' method body. Console.WriteLine() For Each lvi As LocalVariableInfo In mb.LocalVariables Console.WriteLine("Local variable: {0}", lvi) Next ' 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 ' 'Local variable: System.Int32 (0) 'Local variable: System.String (1) 'Local variable: System.ArgumentException (2) 'Local variable: System.Exception (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 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 .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.
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