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Understanding Reflection

Session Code: DVP307

Tamir KhasonTechnology Consultor¹mPrest Systemshttp://blogs.microsoft.co.il/blogs/tamir

¹con·sul·tor (kən sult′ər) - one of a group of priests appointed to advise and assist a bishop

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ExecutionExecution

CompilationCompilation

CLR – compilation and execution

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Source codeSource codeLanguage Language compilercompiler

JIT compilerJIT compiler

Before installation Before installation or the first time or the first time each method is each method is

calledcalled

MSILMSIL

MetadataMetadata

CodeCode

Native codeNative code

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Reflection overview

All types in the CLR are self-describing CLR provides a reader and writer for type definitions

System.Reflection & System.Reflection.emitYou can ‘read’ programs You can map between type systems You can interrogate objects and types inside a running program

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What is “Reflection”?

“Reflection provides objects that encapsulate assemblies, modules, and types.” (MSDN)

“You can use reflection to dynamically create an instance of a type...” (MSDN)

“You can then invoke the type's methods or access its fields and properties.” (MSDN)

“Reflection.Emit namespace contains classes that allow a compiler or tool to emit metadata and Microsoft intermediate language (MSIL)” (MSDN)

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Where is “Reflection”?

System.Reflection namespace contains most Reflection classes.

System.Type is Reflection class used to access type metadata.

…more…

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How to “Reflection”?

Viewing metadata

Performing type discovery

Late binding to methods and properties (Dynamic Invocation)

Creating types at runtime (Reflection Emit)

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How to… perform type discovery

You can use reflection to explore and examine the contents of an assembly programmatically You can find

methods, fields, properties, and events associated with a typesignatures of each of the type's methods;interfaces supported by the type; type's base class.…

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What are you?

Value, Interface or Class?IsValueType, IsInterface, IsClass

Public, Private or Sealed ?IsNotPublic, IsSealed

Abstract or Implementation?IsAbstract

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What you have?

Finding and Exploring MembersMemberInfo: GetMembers(), FindMembers()

Exploring Fields and PropertiesFieldInfo: GetFields(), PropertyInfo: GetProperties()

Exploring Constructors, Methods and EventsGetConstructors(), GetMethods(), GetEvents()

Exploring attributes, determining implemented interfaces, enumerating nested types, …

Everything you may ever want to know

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MemberInfo

Base class for all "member" element descriptions

Fields, Properties, Methods, etc.

Provides member kind, name and declaring class

MemberInfo

MethodBase ParameterInfo FieldInfo EventInfo PropertyInfo

MethodInfo ConstructorInfo

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MethodInfo vs. ConstructorInfo

MethodInfoReturn type and attributesList of all parameters as ParameterInfo arrayDetail implementation information through flag-fieldCan invoke method through Reflection

ConstructorInfoSame features as MethodInfo, just for constructors

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FieldInfo vs. PropertyInfo

FieldInfoField data type and attributesStatic or Instance field, protection levelCan set value through reflection

Provides low-level, direct access with SetValueDirect()

PropertyInfoProperty type and attributesTest methods for readability, writeability"get" and "set" MethodInfoIndexer ParameterInfoCan invoke "set" and "get" through Reflection

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We can clone it…Unknown object

GetType().GetMembers()

For Each MemberFieldInfo.Copy old value to new

Object

Type kidType = oldKid.GetType();

Kid newKid = new Kid();

foreach (var m in kidType.GetProperties()) { m.SetValue(newKid ,

m.GetValue(oldKid, null), null); }

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Clone optimizationUnknown object

GetType().GetMembers()

For Each MemberCreate Code that copies members

Save as Method for later Invocation

Kid CloneKid(Kid){

newKid.Height = oldKid.Height newKid.Weight = oldKid.Weight

}

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Clone optimized

Unknown object

Has custom

method?ExecuteYesYesCopy Members NoNo

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What is… attributes

An attribute is an object that represents data you want to associate with an element in your program.

Two Kinds of Attributes:Intrinsic: Supplied as part of the Common Language Runtime (CLR)Custom: Attributes you create for your own purposes

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Code generation

Using Dynamic InvokeCreate and compile source code in runtimePersistent in diskInvoke Compiler to generate IL

Using Reflection EmitEmit IL code directlyTemporarily stored in memoryBetter performance

Kid CloneKid(Kid){

newKid.Height = oldKid.Height newKid.Weight = oldKid.Weight

}

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CodeDOMCodeEntryPointMethod start = new CodeEntryPointMethod();

CodeMethodInvokeExpression cs1 = new CodeMethodInvokeExpression( new CodeTypeReferenceExpression("System.Console"), "WriteLine", new CodePrimitiveExpression("Hello World!") );

start.Statements.Add(cs1);

public static void Main(){

System.Console.WriteLine(“Hello World!”);}

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CodeDOM

CodeArgumentReferenceExpressionCodeArrayCreateExpressionCodeArrayIndexerExpressionCodeAssignStatementCodeAttachEventStatementCodeAttributeArgumentCodeAttributeArgumentCollectionCodeAttributeDeclarationCodeAttributeDeclarationCollectionCodeBaseReferenceExpressionCodeBinaryOperatorExpressionCodeCastExpressionCodeCatchClauseCodeCatchClauseCollectionCodeCommentCodeCommentStatementCodeCommentStatementCollectionCodeCompileUnitCodeConditionStatementCodeConstructorCodeDelegateCreateExpression

CodeExpressionCollectionCodeExpressionStatementCodeFieldReferenceExpressionCodeGotoStatementCodeIndexerExpressionCodeIterationStatementCodeLabeledStatementCodeLinePragmaCodeMemberEventCodeMemberFieldCodeMemberMethodCodeMemberPropertyCodeMethodInvokeExpressionCodeMethodReferenceExpressionCodeMethodReturnStatementCodeNamespaceCodeNamespaceCollectionCodeNamespaceImportCodeNamesapceImportCollectionCodeObjectCodeObjectCreateExpression

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CodeDOM – even moreCodeCompilerCodeDomProviderCodeGeneratorCodeGeneratorOptionsCodeParserCompilerErrorCompilerErrorCollectionCompilerParametersCompilerResultsExecutorIndentedTextWriterTempFileCollection

ICodeCompilerICodeGeneratorICodeParser

CodeBinaryOperatorTypeFieldDirectionMemberAttributes

CodePropertySetValueReferenceExpressionCodeRemoveEventStatementCodeSnippetCompileUnitCodeSnippetExpressionCodeTypeMemberCollectionCodeTypeOfExpressionCodeTypeReferenceCodeTypeReferenceCollectionCodeTypeReferenceExpressionCodeVariableDeclarationStatementCodeVariableReferenceExpression

CodeCatchClauseCodeCatchClauseCollectionCodeCommentCodeCommentStatementCodeCommentStatementCollectionCodeCompileUnitCodeConditionStatementCodeConstructorCodeDelegateCreateExpressionCodeDelegateInvokeExpressionCodeDirectionExpressionCodeEntryPointMethod

CodeEventReferenceExpressionCodeExpressionCodeSnippetStatementCodeSnippetTypeMemberCodeStatementCollectionCodeThisReferenceExpressionCodeThrowExceptionStatementCodeTryCatchFinallyStatementCodeTypeConstructorCodeTypeDeclarationCodeTypeDeclarationCollectionCodeTypeDelegateCodeTypeMember

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•Dynamic Invocation with Brut force Dynamic Invocation with Brut force compilationcompilation

•Dynamic Invocation with Brut force Dynamic Invocation with Brut force CodeDOMCodeDOM•Dynamic Invocation with CodeDOMDynamic Invocation with CodeDOM

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CodeDOM – Bottom line

A lot of goodies, but very complicated yet limited

…also you can write your ownCodeDomProvider

…however, if you can generate the CodeDom, it does not mean you can generate code with it

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IL introduction

IL – The language for executionIndependent of CPU and platform

Created by Microsoft, external commercial and academic language/compiler writers

Stack based virtual machine:5 + 10 - 3 5 + 10 - 3

IL_0001: ldc.i4 5IL_0001: ldc.i4 5 IL_0002: ldc.i4 10 IL_0002: ldc.i4 10 IL_0003: addIL_0003: add IL_0004: ldc.i4 3IL_0004: ldc.i4 3 IL_0005: subIL_0005: sub Evaluation StackEvaluation Stack

0000 0050000 005

0000 00100000 0010

0000 00150000 0015

0000 00030000 0003

0000 00120000 0012

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IL introduction

IL storage opcodesLocals of a method

Fields in a class

string str = “Hello, World!”string str = “Hello, World!” IL_0001: ldstr “Hello, World!”IL_0001: ldstr “Hello, World!” IL_0002: stloc strIL_0002: stloc str IL_0003: ldloc str IL_0003: ldloc str

Foo.f = “Hello, World!”Foo.f = “Hello, World!” IL_0001: ldstr “Hello, World!”IL_0001: ldstr “Hello, World!” IL_0002: stfld string Foo::fIL_0002: stfld string Foo::f IL_0003: ldfld string Foo::fIL_0003: ldfld string Foo::f

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IL introduction

IL control flow opcodesif (b) { ... } else { ... } if (b) { ... } else { ... }

IL_0001: ldloc bIL_0001: ldloc b IL_0002: ldc.i4.1IL_0002: ldc.i4.1 IL_0003: ceqIL_0003: ceq IL_0004: brfalse IL_00020IL_0004: brfalse IL_00020 // if true statements// if true statements IL_0010: ...IL_0010: ... IL_0011: br IL_00025IL_0011: br IL_00025 // else statements// else statements IL_0020: ...IL_0020: ... // rest of method// rest of method IL_0025: ...IL_0025: ...

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Reflection.Emit

AssemblybuilderConstructorBuilderCustomAttributeBuilderEnumBuilderEventBuilderFieldBuilderILGenerator

Label LocalBuilder MethodBuilder ModuleBuilder ParameterBuilder PropertyBuilder TypeBuilder

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Code Emittingpublic class MyClass {

public static void Main() {string str = “Hello World!”;Console.WriteLine (str);

}}

AssemblyBuilderAssemblyBuilder

ModuleBuilderModuleBuilder

TypeBuilderTypeBuilder

MethodBuilderMethodBuilder

LocalBuilderLocalBuilder

ILGeneratorILGeneratorOPCodesOPCodes

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Lightweight Code Generation

DynamicMethod

Kid CloneKid(Kid){

newKid.Height = oldKid.Height newKid.Weight = oldKid.Weight

}

DynamicMethodDynamicMethodILGeneratorILGeneratorOPCodesOPCodes

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•Dynamic Invocation with EmitDynamic Invocation with Emit

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HackMe

All types in the CLR are self-describing

DynamicMethod dm =…dm.GetMethodBody().GetILAsByteArray();

MethodInfo mi = ..mi.GetMethodBody().GetILAsByteArray();

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What's new in .NET 3.5?

Lambdas.Compile() for code generation

Expression TreesParse and understand

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From delegate to LambdaDelegate void SomeDelegate(EventsArgs e);

Object.SomeEvent += new SomeDelegate(SomeMethod);

DelegateDelegate

Object.SomeEvent += delegate(EventArgs e) { //work here }

Anonymous delegate Anonymous delegate

Object.SomeEvent += (e) => { //work here };LambdaLambda

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Expression Tree

Use Expression<T>

Parse Lambdas at runtime

Compile at runtime (Expression.Compile())

Use the Expression Tree Debug Visualizerhttp://code.msdn.microsoft.com/csharpsamples

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•Parse and visualize treesParse and visualize trees •Compile LambdasCompile Lambdas

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© 2008 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS,

IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.