Imports System
Imports System.Threading
Imports System.Reflection
Imports System.Reflection.Emit
_
Class EmitWriteLineDemo
Public Shared Function CreateDynamicType() As Type
Dim ctorParams() As Type = {GetType(Integer), GetType(Integer)}
Dim myDomain As AppDomain = Thread.GetDomain()
Dim myAsmName As New AssemblyName()
myAsmName.Name = "MyDynamicAssembly"
Dim myAsmBuilder As AssemblyBuilder = myDomain.DefineDynamicAssembly(myAsmName, AssemblyBuilderAccess.RunAndSave)
Dim pointModule As ModuleBuilder = myAsmBuilder.DefineDynamicModule("PointModule", "Point.dll")
Dim pointTypeBld As TypeBuilder = pointModule.DefineType("Point", _
TypeAttributes.Public)
Dim xField As FieldBuilder = pointTypeBld.DefineField("x", _
GetType(Integer), _
FieldAttributes.Public)
Dim yField As FieldBuilder = pointTypeBld.DefineField("y", _
GetType(Integer), _
FieldAttributes.Public)
Dim objType As Type = Type.GetType("System.Object")
Dim objCtor As ConstructorInfo = objType.GetConstructor(New Type(){})
Dim pointCtor As ConstructorBuilder = pointTypeBld.DefineConstructor( _
MethodAttributes.Public, _
CallingConventions.Standard, _
ctorParams)
Dim ctorIL As ILGenerator = pointCtor.GetILGenerator()
' First, you build the constructor.
ctorIL.Emit(OpCodes.Ldarg_0)
ctorIL.Emit(OpCodes.Call, objCtor)
ctorIL.Emit(OpCodes.Ldarg_0)
ctorIL.Emit(OpCodes.Ldarg_1)
ctorIL.Emit(OpCodes.Stfld, xField)
ctorIL.Emit(OpCodes.Ldarg_0)
ctorIL.Emit(OpCodes.Ldarg_2)
ctorIL.Emit(OpCodes.Stfld, yField)
ctorIL.Emit(OpCodes.Ret)
' Now, you'll build a method to output some information on the
' inside your dynamic class. This method will have the following
' definition in C#:
' Public Sub WritePoint()
Dim writeStrMthd As MethodBuilder = pointTypeBld.DefineMethod("WritePoint", _
MethodAttributes.Public, _
Nothing, Nothing)
Dim writeStrIL As ILGenerator = writeStrMthd.GetILGenerator()
' The below ILGenerator created demonstrates a few ways to create
' string output through STDIN.
' ILGenerator.EmitWriteLine(string) will generate a ldstr and a
' call to WriteLine for you.
writeStrIL.EmitWriteLine("The value of this current instance is:")
' Here, you will do the hard work yourself. First, you need to create
' the string we will be passing and obtain the correct WriteLine overload
' for said string. In the below case, you are substituting in two values,
' so the chosen overload is Console.WriteLine(string, object, object).
Dim inStr As [String] = "({0}, {1})"
Dim wlParams() As Type = {GetType(String), GetType(Object), GetType(Object)}
' We need the MethodInfo to pass into EmitCall later.
Dim writeLineMI As MethodInfo = GetType(Console).GetMethod("WriteLine", wlParams)
' Push the string with the substitutions onto the stack.
' This is the first argument for WriteLine - the string one.
writeStrIL.Emit(OpCodes.Ldstr, inStr)
' Since the second argument is an object, and it corresponds to
' to the substitution for the value of our integer field, you
' need to box that field to an object. First, push a reference
' to the current instance, and then push the value stored in
' field 'x'. We need the reference to the current instance (stored
' in local argument index 0) so Ldfld can load from the correct
' instance (this one).
writeStrIL.Emit(OpCodes.Ldarg_0)
writeStrIL.Emit(OpCodes.Ldfld, xField)
' Now, we execute the box opcode, which pops the value of field 'x',
' returning a reference to the integer value boxed as an object.
writeStrIL.Emit(OpCodes.Box, GetType(Integer))
' Atop the stack, you'll find our string inStr, followed by a reference
' to the boxed value of 'x'. Now, you need to likewise box field 'y'.
writeStrIL.Emit(OpCodes.Ldarg_0)
writeStrIL.Emit(OpCodes.Ldfld, yField)
writeStrIL.Emit(OpCodes.Box, GetType(Integer))
' Now, you have all of the arguments for your call to
' Console.WriteLine(string, object, object) atop the stack:
' the string InStr, a reference to the boxed value of 'x', and
' a reference to the boxed value of 'y'.
' Call Console.WriteLine(string, object, object) with EmitCall.
writeStrIL.EmitCall(OpCodes.Call, writeLineMI, Nothing)
' Lastly, EmitWriteLine can also output the value of a field
' using the overload EmitWriteLine(FieldInfo).
writeStrIL.EmitWriteLine("The value of 'x' is:")
writeStrIL.EmitWriteLine(xField)
writeStrIL.EmitWriteLine("The value of 'y' is:")
writeStrIL.EmitWriteLine(yField)
' Since we return no value (void), the the ret opcode will not
' return the top stack value.
writeStrIL.Emit(OpCodes.Ret)
Return pointTypeBld.CreateType()
End Function 'CreateDynamicType
Public Shared Sub Main()
Dim ctorParams(1) As Object
Console.Write("Enter a integer value for X: ")
Dim myX As String = Console.ReadLine()
Console.Write("Enter a integer value for Y: ")
Dim myY As String = Console.ReadLine()
Console.WriteLine("---")
ctorParams(0) = Convert.ToInt32(myX)
ctorParams(1) = Convert.ToInt32(myY)
Dim ptType As Type = CreateDynamicType()
Dim ptInstance As Object = Activator.CreateInstance(ptType, ctorParams)
ptType.InvokeMember("WritePoint", _
BindingFlags.InvokeMethod, _
Nothing, ptInstance, Nothing)
End Sub 'Main
End Class 'EmitWriteLineDemo