Imports System
Imports System.Threading
Imports System.Reflection
Imports System.Reflection.Emit
_
Class TestCtorBuilder
Public Shared Function DynamicPointTypeGen() As Type
Dim pointType As Type = Nothing
Dim ctorParams() As Type = {GetType(Integer), 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 zField As FieldBuilder = pointTypeBld.DefineField("z", 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()
' NOTE: ldarg.0 holds the "this" reference - ldarg.1, ldarg.2, and ldarg.3
' hold the actual passed parameters. ldarg.0 is used by instance methods
' to hold a reference to the current calling object instance. Static methods
' do not use arg.0, since they are not instantiated and hence no reference
' is needed to distinguish them.
ctorIL.Emit(OpCodes.Ldarg_0)
' Here, we wish to create an instance of System.Object by invoking its
' constructor, as specified above.
ctorIL.Emit(OpCodes.Call, objCtor)
' Now, we'll load the current instance ref in arg 0, along
' with the value of parameter "x" stored in arg 1, into stfld.
ctorIL.Emit(OpCodes.Ldarg_0)
ctorIL.Emit(OpCodes.Ldarg_1)
ctorIL.Emit(OpCodes.Stfld, xField)
' Now, we store arg 2 "y" in the current instance with stfld.
ctorIL.Emit(OpCodes.Ldarg_0)
ctorIL.Emit(OpCodes.Ldarg_2)
ctorIL.Emit(OpCodes.Stfld, yField)
' Last of all, arg 3 "z" gets stored in the current instance.
ctorIL.Emit(OpCodes.Ldarg_0)
ctorIL.Emit(OpCodes.Ldarg_3)
ctorIL.Emit(OpCodes.Stfld, zField)
' Our work complete, we return.
ctorIL.Emit(OpCodes.Ret)
' Now, let's create three very simple methods so we can see our fields.
Dim mthdNames() As String = {"GetX", "GetY", "GetZ"}
Dim mthdName As String
For Each mthdName In mthdNames
Dim getFieldMthd As MethodBuilder = pointTypeBld.DefineMethod(mthdName, MethodAttributes.Public, GetType(Integer), Nothing)
Dim mthdIL As ILGenerator = getFieldMthd.GetILGenerator()
mthdIL.Emit(OpCodes.Ldarg_0)
Select Case mthdName
Case "GetX"
mthdIL.Emit(OpCodes.Ldfld, xField)
Case "GetY"
mthdIL.Emit(OpCodes.Ldfld, yField)
Case "GetZ"
mthdIL.Emit(OpCodes.Ldfld, zField)
End Select
mthdIL.Emit(OpCodes.Ret)
Next mthdName
' Finally, we create the type.
pointType = pointTypeBld.CreateType()
' Let's save it, just for posterity.
myAsmBuilder.Save("Point.dll")
Return pointType
End Function 'DynamicPointTypeGen
Public Shared Sub Main()
Dim myDynamicType As Type = Nothing
Dim aPoint As Object = Nothing
Dim aPtypes() As Type = {GetType(Integer), GetType(Integer), GetType(Integer)}
Dim aPargs() As Object = {4, 5, 6}
' Call the method to build our dynamic class.
myDynamicType = DynamicPointTypeGen()
Console.WriteLine("Some information about my new Type '{0}':", myDynamicType.FullName)
Console.WriteLine("Assembly: '{0}'", myDynamicType.Assembly)
Console.WriteLine("Attributes: '{0}'", myDynamicType.Attributes)
Console.WriteLine("Module: '{0}'", myDynamicType.Module)
Console.WriteLine("Members: ")
Dim member As MemberInfo
For Each member In myDynamicType.GetMembers()
Console.WriteLine("-- {0} {1};", member.MemberType, member.Name)
Next member
Console.WriteLine("---")
' Let's take a look at the constructor we created.
Dim myDTctor As ConstructorInfo = myDynamicType.GetConstructor(aPtypes)
Console.WriteLine("Constructor: {0};", myDTctor.ToString())
Console.WriteLine("---")
' Now, we get to use our dynamically-created class by invoking the constructor.
aPoint = myDTctor.Invoke(aPargs)
Console.WriteLine("aPoint is type {0}.", aPoint.GetType())
' Finally, let's reflect on the instance of our new type - aPoint - and
' make sure everything proceeded according to plan.
Console.WriteLine("aPoint.x = {0}", myDynamicType.InvokeMember("GetX", BindingFlags.InvokeMethod, Nothing, aPoint, New Object() {}))
Console.WriteLine("aPoint.y = {0}", myDynamicType.InvokeMember("GetY", BindingFlags.InvokeMethod, Nothing, aPoint, New Object() {}))
Console.WriteLine("aPoint.z = {0}", myDynamicType.InvokeMember("GetZ", BindingFlags.InvokeMethod, Nothing, aPoint, New Object() {}))
End Sub 'Main
End Class 'TestCtorBuilder
' +++ OUTPUT +++
' Some information about my new Type 'Point':
' Assembly: 'MyDynamicAssembly, Version=0.0.0.0'
' Attributes: 'AutoLayout, AnsiClass, NotPublic, Public'
' Module: 'PointModule'
' Members:
' -- Field x;
' -- Field y;
' -- Field z;
' -- Method GetHashCode;
' -- Method Equals;
' -- Method ToString;
' -- Method GetType;
' -- Constructor .ctor;
' ---
' Constructor: Void .ctor(Int32, Int32, Int32);
' ---
' aPoint is type Point.
' aPoint.x = 4
' aPoint.y = 5
' aPoint.z = 6