ILGenerator.DefineLabel Methode
Definitie
Belangrijk
Bepaalde informatie heeft betrekking op een voorlopige productversie die aanzienlijk kan worden gewijzigd voordat deze wordt uitgebracht. Microsoft biedt geen enkele expliciete of impliciete garanties met betrekking tot de informatie die hier wordt verstrekt.
Declareert een nieuw label.
public:
virtual System::Reflection::Emit::Label DefineLabel();public virtual System.Reflection.Emit.Label DefineLabel();abstract member DefineLabel : unit -> System.Reflection.Emit.Label
override this.DefineLabel : unit -> System.Reflection.Emit.LabelPublic Overridable Function DefineLabel () As LabelRetouren
Een nieuw label dat kan worden gebruikt als een token voor vertakking.
Voorbeelden
In het onderstaande codevoorbeeld ziet u het contextuele gebruik van de DefineLabel methode.
using System;
using System.Threading;
using System.Reflection;
using System.Reflection.Emit;
class ILLabelDemo {
public static Type BuildAdderType() {
AppDomain myDomain = Thread.GetDomain();
AssemblyName myAsmName = new AssemblyName();
myAsmName.Name = "AdderExceptionAsm";
AssemblyBuilder myAsmBldr = myDomain.DefineDynamicAssembly(myAsmName,
AssemblyBuilderAccess.Run);
ModuleBuilder myModBldr = myAsmBldr.DefineDynamicModule("AdderExceptionMod");
TypeBuilder myTypeBldr = myModBldr.DefineType("Adder");
Type[] adderParams = new Type[] {typeof(int), typeof(int)};
// This method will add two numbers which are 100 or less. If either of the
// passed integer vales are greater than 100, it will return the value of -1.
MethodBuilder adderBldr = myTypeBldr.DefineMethod("DoAdd",
MethodAttributes.Public |
MethodAttributes.Static,
typeof(int),
adderParams);
ILGenerator adderIL = adderBldr.GetILGenerator();
// In order to successfully branch, we need to create labels
// representing the offset IL instruction block to branch to.
// These labels, when the MarkLabel(Label) method is invoked,
// will specify the IL instruction to branch to.
Label failed = adderIL.DefineLabel();
Label endOfMthd = adderIL.DefineLabel();
// First, load argument 0 and the integer value of "100" onto the
// stack. If arg0 > 100, branch to the label "failed", which is marked
// as the address of the block that loads -1 onto the stack, bypassing
// the addition.
adderIL.Emit(OpCodes.Ldarg_0);
adderIL.Emit(OpCodes.Ldc_I4_S, 100);
adderIL.Emit(OpCodes.Bgt_S, failed);
// Now, check to see if argument 1 was greater than 100. If it was,
// branch to "failed." Otherwise, fall through and perform the addition,
// branching unconditionally to the instruction at the label "endOfMthd".
adderIL.Emit(OpCodes.Ldarg_1);
adderIL.Emit(OpCodes.Ldc_I4_S, 100);
adderIL.Emit(OpCodes.Bgt_S, failed);
adderIL.Emit(OpCodes.Ldarg_0);
adderIL.Emit(OpCodes.Ldarg_1);
adderIL.Emit(OpCodes.Add_Ovf_Un);
adderIL.Emit(OpCodes.Br_S, endOfMthd);
// If this label is branched to (the failure case), load -1 onto the stack
// and fall through to the return opcode.
adderIL.MarkLabel(failed);
adderIL.Emit(OpCodes.Ldc_I4_M1);
// The end of the method. If both values were less than 100, the
// correct result will return. If one of the arguments was greater
// than 100, the result will be -1.
adderIL.MarkLabel(endOfMthd);
adderIL.Emit(OpCodes.Ret);
return myTypeBldr.CreateType();
}
public static void Main() {
Type adderType = BuildAdderType();
object addIns = Activator.CreateInstance(adderType);
object[] addParams = new object[2];
Console.Write("Enter an integer value: ");
addParams[0] = (object)Convert.ToInt32(Console.ReadLine());
Console.Write("Enter another integer value: ");
addParams[1] = (object)Convert.ToInt32(Console.ReadLine());
Console.WriteLine("---");
int adderResult = (int)adderType.InvokeMember("DoAdd",
BindingFlags.InvokeMethod,
null,
addIns,
addParams);
if (adderResult != -1) {
Console.WriteLine("{0} + {1} = {2}", addParams[0], addParams[1],
adderResult);
} else {
Console.WriteLine("One of the integers to add was greater than 100!");
}
}
}
Imports System.Threading
Imports System.Reflection
Imports System.Reflection.Emit
_
Class ILLabelDemo
Public Shared Function BuildAdderType() As Type
Dim myDomain As AppDomain = Thread.GetDomain()
Dim myAsmName As New AssemblyName()
myAsmName.Name = "AdderExceptionAsm"
Dim myAsmBldr As AssemblyBuilder = myDomain.DefineDynamicAssembly(myAsmName, _
AssemblyBuilderAccess.Run)
Dim myModBldr As ModuleBuilder = myAsmBldr.DefineDynamicModule("AdderExceptionMod")
Dim myTypeBldr As TypeBuilder = myModBldr.DefineType("Adder")
Dim adderParams() As Type = {GetType(Integer), GetType(Integer)}
' This method will add two numbers which are 100 or less. If either of the
' passed integer vales are greater than 100, it will return the value of -1.
Dim adderBldr As MethodBuilder = myTypeBldr.DefineMethod("DoAdd", _
MethodAttributes.Public Or MethodAttributes.Static, _
GetType(Integer), adderParams)
Dim adderIL As ILGenerator = adderBldr.GetILGenerator()
' In order to successfully branch, we need to create labels
' representing the offset IL instruction block to branch to.
' These labels, when the MarkLabel(Label) method is invoked,
' will specify the IL instruction to branch to.
Dim failed As Label = adderIL.DefineLabel()
Dim endOfMthd As Label = adderIL.DefineLabel()
' First, load argument 0 and the integer value of "100" onto the
' stack. If arg0 > 100, branch to the label "failed", which is marked
' as the address of the block that loads -1 onto the stack, bypassing
' the addition.
adderIL.Emit(OpCodes.Ldarg_0)
adderIL.Emit(OpCodes.Ldc_I4_S, 100)
adderIL.Emit(OpCodes.Bgt_S, failed)
' Now, check to see if argument 1 was greater than 100. If it was,
' branch to "failed." Otherwise, fall through and perform the addition,
' branching unconditionally to the instruction at the label "endOfMthd".
adderIL.Emit(OpCodes.Ldarg_1)
adderIL.Emit(OpCodes.Ldc_I4_S, 100)
adderIL.Emit(OpCodes.Bgt_S, failed)
adderIL.Emit(OpCodes.Ldarg_0)
adderIL.Emit(OpCodes.Ldarg_1)
adderIL.Emit(OpCodes.Add_Ovf_Un)
adderIL.Emit(OpCodes.Br_S, endOfMthd)
' If this label is branched to (the failure case), load -1 onto the stack
' and fall through to the return opcode.
adderIL.MarkLabel(failed)
adderIL.Emit(OpCodes.Ldc_I4_M1)
' The end of the method. If both values were less than 100, the
' correct result will return. If one of the arguments was greater
' than 100, the result will be -1.
adderIL.MarkLabel(endOfMthd)
adderIL.Emit(OpCodes.Ret)
Return myTypeBldr.CreateType()
End Function 'BuildAdderType
Public Shared Sub Main()
Dim adderType As Type = BuildAdderType()
Dim addIns As Object = Activator.CreateInstance(adderType)
Dim addParams(1) As Object
Console.Write("Enter an integer value: ")
addParams(0) = CType(Convert.ToInt32(Console.ReadLine()), Object)
Console.Write("Enter another integer value: ")
addParams(1) = CType(Convert.ToInt32(Console.ReadLine()), Object)
Console.WriteLine("---")
Dim adderResult As Integer = CInt(adderType.InvokeMember("DoAdd", _
BindingFlags.InvokeMethod, Nothing, _
addIns, addParams))
If adderResult <> - 1 Then
Console.WriteLine("{0} + {1} = {2}", addParams(0), addParams(1), adderResult)
Else
Console.WriteLine("One of the integers to add was greater than 100!")
End If
End Sub
End Class
Opmerkingen
Als u de positie van het label in de stream wilt instellen, moet u aanroepen MarkLabel. Als u dit niet doet, wordt er een ArgumentException aangeroepen.TypeBuilder.CreateType
Dit is slechts een token en vertegenwoordigt nog geen bepaalde locatie in de stream.