All types in the CLR are self-describing

1
Reflection Overview

• All types in the CLR are self-describing
• CLR provides a reader and writer for type
  definitions
• System.Reflection System.Reflection.emit
• You can read programs
• You can map between type systems
• You can interrogate objects and types inside a
  running program

2
Execution model
VB
Cobol
C
C
.NET languages
Language compilers
CIL code ( metadata)
Loader/verifier
JIT compiler
Uncompiled method call
Managed Code
Execution
3
Reflection Core Concepts

• Metadata
• Single location for type information and code
• Code is literally contained within type
  information
• Every .NET object can be queried for its type
• Type metadata can be explored with Reflection
• Dynamic Type System
• Highly dynamic and language independent
• Types may be extended and built at run time
• Allows on-the-fly creation of assemblies
• See my CodeDom tutorial http//www.codeproject.co
  m/KB/dotnet/CodeDomDelegates.aspx

4
Metadata uses

• Allows type developed in a PL to be used by code
  in other PL
• GC uses to traverse objects
• Serialization (essential for Web Services)
• IDE (e.g. IntelliSense)

5
Exploring Metadata

• Who are you?
• What are you?
• Anything special about you?
• Now tell me what you have!
• Types and Instances

6
System.Type

• Access to meta-data for any .NET type
• Returned by System.Object.GetType()
• Allows drilling down into all facets of a type
• Category Simple, Enum, Struct or Class
• Methods and Constructors, Parameters and Return
• Fields and Properties, Arguments and Attributes
• Events, Delegates and Namespaces
• C also has the, typeof(), is and as operators.

7
What are you?

• Value, Interface or Class?
• IsValueType, IsInterface, IsClass
• Public, Private or Sealed ?
• IsNotPublic, IsSealed
• Abstract or Implementation?
• IsAbstract
• Covers all possible properties of a managed type
• Very intuitive API, no "Parameter Hell"

8
Type Reflection
Savings.BaseType Account Savings.BaseType.BaseTy
pe Object ITransfer.BaseType
null Account.IsSubClassof(IEnquire)
false Savings.IsSubClassof(Account)
true Savings.GetInterfaces() IPrint,
ITransfer, IEnquire IEnquire.IsAssignableFrom(S
avings) true

Object
9
Reflection and the CLR type system
System.Object
ParameterInfo
MemberInfo
Module
Assembly
EventInfo
PropertyInfo
FieldInfo
MethodBase
System.Type
MethodInfo
ConstructorInfo
10
MetaData Type Info at Runtime
serializablepublic class Person
public event OnSaveChange onsv public Date
DOB public string FirstName public
string LastName public string Name
get return FirstName " "
LastName public
Person(string First,string Last)
FirstNameFirstLastNameLast public
bool Save() System.Type t
this.GetType() foreach( FieldInfo f in
t.GetFields() ) ...
System.Type
Attributes
Events
Fields
Properties
Constructors
Parameters
Methods
11
Reflection MetaData Samples

• // Test sample classpublic class Test
• private int n
• public Test(int a) na
• public void Foo(float a, object b, string c)
  
• //Retrieve the Type object
• public static int Main(string args)
• Type type1 typeof(Test)
• Test t1 new Test(0)
• Type type2 t1.GetType()
• Console.WriteLine(type of t1 is 0, type2)
• return 0

Note type1type2 ReferenceEquals(type1, type2)
true
12
ReflectionType and Instances

• Type Safety First! Type checking at run time
• if (o is Customer)
• Dynamic Invocation through Reflection
• Support for late binding
• MethodInfo.Invoke()
• FieldInfo.SetValue()

13
ReflectionGetMethods Example

• //Get a list of methods supported by a class
• public static int Main(string args)
• Type type1 typeof(Test)
• MethodInfo minf type1.GetMethods()
• foreach (MethodInfo m in minf)
• //Print out the method name and whether it is
  public
• Console.WriteLine(Name m.Name ,
• ((m.IsPublic) ? public )
  ((m.IsVirtual) ? virtual )
• //Get the list of parameters
• ParameterInfo pi m.GetParameters()
• foreach (ParameterInfo p in pi)
• Console.WriteLine( p.ParameterType
  p.Name)
• return 0

Name Foo, public System.Single a
System.Object b System.String c Name
GetType, public Name ToString, public
virtual Name Equals, public virtual
System.Object obj Name GetHashCode, public
virtual Press any key to continue . . .
14
ReflectionMemberInfo

• 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
15
Anything special about you?

• Special Memory Layout?
• IsAutoLayout
• IsExplicitLayout
• IsLayoutSequential
• COM Objects?
• IsCOMObject
• More
• IsUnicodeClass
• IsSpecialName, etc.

16
Now tell me what you have!

• Finding and Exploring Members
• MemberInfo GetMembers(), FindMembers()
• Exploring Fields and Properties
• FieldInfo GetFields(), PropertyInfo
  GetProperties()
• Exploring Constructors, Methods and Events
• GetConstructors(), GetMethods(), GetEvents()
• Exploring attributes, determining implemented
  interfaces, enumerating nested types,
• Summary Everything you may ever want to know

17
Type and Instances

• Type Safety First! Type checking at runtime
• C if (o is Customer)
• VB If TypeOf o Is Customer Then End If
• Dynamic Invocation through Reflection
• Support for late binding
• MethodInfo.Invoke()
• FieldInfo.SetValue()
• PropertyInfo.SetValue()

18
Reflection Dynamic Creation Example

• You can use CreateInstance and other methods to
  create instances at run-time and call their
  methods and properties.
• See the example here for more info.
• http//www.csharp-examples.net/reflection-examples
  /

19
ReflectionThe Bigger Picture

• Types know their module modules know their types
• Modules know their assembly and vice versa
• Code can browse and search its entire context

Assembly
Module
Module
Module
Struct
Delegate
Class
Constructor
Class
Class
Method
Interface
Interface
Method
Field
Interface
Class
20
Traverse every element in an assembly
Using System.Reflection public static void
WalkAssembly(String assemblyName) Assembly
assembly Assembly.Load (assemblyName)
foreach (Module module in assembly.GetModules())
foreach (Type type in module.GetTypes())
foreach (MemberInfo member in
type.GetMembers()) Console.WriteLine
(0.1, type, member.Name
21
Object Creation

• OK, now see my CodeDom tutorial
  http//www.codeproject.com/KB/dotnet/CodeDomDeleg
  ates.aspx

22
Serialization

• Save state of an object on disk or send to a
  stream (we will cover this more later)
• public class Point
• public double x
• public double y
• public double length // computed from x, y

23
Solutions

• Inherit from a base type
• class Point Serializable
• but
• base type does not know derived type
• requires multiple inheritance
• Java solution
• class Point implements Serializable
• but
• method granularity
• customization requires full rewrite of
  WriteObject, ReadObject

24
Solution Attributes

• Serializable
• public class Point
• public double x
• public double y
• NonSerialized
• public double length // computed from x, y

25
ReflectionSummary

• Reflection System.Type GetType()
• Explore type information at runtime
• Enables attribute-driven programming
• Bottom line Fully self-contained structural
  model
• Used extensively in Visual Studio

26
VisualStudio.NET and Reflection
Toolbox
Component Class
Description
Properties Window
DefaultValue
Help
Localizable
Designers
ReadOnly
Help
ComponentModel Attributes
27
System.AddIn

• There is a new set of classes in the System.AddIn
  namespace for aiding in plug-in architectures.
• I have not had a chance to look at this closely,
  but it appears to be more for creating Adapters
  (see the Adapter design pattern) and creating a
  common interface (called an IContract). In other
  words allowing a plug-in that did not support
  your interface in the first place.
• See http//blogs.microsoft.co.il/blogs/bursteg/arc
  hive/2007/08/13/Build-AddIns-with-System-AddIn.asp
  x.