ABHISHEK BISWAS

.NET ReflectionDynamically Create, Find and

Invoke Types

References

Video: https://www.youtube.com/watch?v=y8-uq6Ur7Dc

https://www.youtube.com/watch?v=-wKqwAJ-ipg

.NET Reflection

Features Create and Extend types, modules & assemblies at

runtime Read type metadata at runtime Invoke type methods at runtime Language Independent

Advantages Single location for type information and code Code is contained within type information Every .NET object can be queried for its type

Metadata Components

Reflection at Work

Assembly assm = appDomain.Load(buffer);

Type[] types = assm.GetTypes();

foreach (Type type in types)

{Console.WriteLine(type.FullName); }

MethodInfo myMethod = assm.GetType("HW3.hashKey").

GetMethod("GenHash");

object obj = Activator.CreateInstance

(assm.GetType("HW3.hashKey"));

myMethod.Invoke(obj, null);

GetType() Function Breakdown

Member of System.Object Parent of all .NET classes

Available on every .NET class & simple type

Returns System.Type object

Type Identity Types have unique identity across any assembly

Types can be compared for identity

• if ( a.GetType() == b.GetType() ) { … };

System.Type

Access to meta-data for any .NET typeAllows drilling down into all facets of a typeCategory: Simple, Enum, Struct or Class

IsValueType, IsInterface, IsClass IsNotPublic, IsSealed IsAbstract

Methods and Constructors, Parameters and Return MemberInfo: GetMembers(), FindMembers() FieldInfo: GetFields(), PropertyInfo: GetProperties() GetConstructors(), GetMethods(), GetEvents()

Fields and Properties, Arguments and AttributesEvents, Delegates and Namespaces

Invoking Methods

Dynamic Invocation through Reflection

Support for late binding

MethodInfo.Invoke()

FieldInfo.SetValue()

PropertyInfo.SetValue()

Creating a New Type/Module/Assembly

Namespace “System.Reflection.Emit”Dim aName As New AssemblyName("DynamicAssemblyExample")

Dim ab As AssemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(aName, AssemblyBuilderAccess.RunAndSave)

Dim mb As ModuleBuilder = ab.DefineDynamicModule(aName.Name, aName.Name & ".dll")

Dim tb As TypeBuilder = mb.DefineType("MyDynamicType", TypeAttributes.Public)

Adding Field and Constructor

Dim fbNumber As FieldBuilder = tb.DefineField("m_number“, GetType(Integer), FieldAttributes.Private)

Dim parameterTypes() As Type = { GetType(Integer) }

Dim ctor1 As ConstructorBuilder = tb.DefineConstructor( MethodAttributes.Public, CallingConventions.Standard, parameterTypes)

Dim ctor1IL As ILGenerator = ctor1.GetILGenerator()ctor1IL.Emit(OpCodes.Ldarg_0) ctor1IL.Emit(OpCodes.Call,GetType(Object).GetConstructor(Type.EmptyT

ypes)) ctor1IL.Emit(OpCodes.Ldarg_0) ctor1IL.Emit(OpCodes.Ldarg_1)ctor1IL.Emit(OpCodes.Stfld, fbNumber) ctor1IL.Emit(OpCodes.Ret)

Adding Method

Dim meth As MethodBuilder = tb.DefineMethod("MyMethod", MethodAttributes.Public,

GetType(Integer), New Type(){GetType(Integer)})

Dim methIL As ILGenerator = meth.GetILGenerator()methIL.Emit(OpCodes.Ldarg_0)methIL.Emit(OpCodes.Ldfld, fbNumber) methIL.Emit(OpCodes.Ldarg_1) methIL.Emit(OpCodes.Mul) methIL.Emit(OpCodes.Ret)

Finishing

Dim t As Type = tb.CreateType()

ab.Save(aName.Name & ".dll")

Dim mi As MethodInfo = t.GetMethod("MyMethod")

Dim pi As PropertyInfo = t.GetProperty("Number")

Why?

Build classes dynamically from script-like code ASP.NET, Regular Expressions do just that !

Generate code from visual development tools e.g. build interfaces, base classes from UML

Create dynamic wrappers for existing codeTransfer code-chunks to remote machines

Distributed processing scenarios

References

http://www.dcl.hpi.uni-potsdam.de/teaching/componentVl05/slides/Net_VL2_02_Reflection.pdf

http://msdn.microsoft.com/en-us/library/system.reflection.emit.assemblybuilder%28v=VS.100%29.asp