Introduction to .NET Reflection
Reflection is ability to find information about types contained in an
assembly at run time. Prior to .NET languages like C++ provided such
ability in a limited sense. .NET provides a whole new set of APIs to introspect
assemblies and objects. All the APIs related to reflection are located under
System.Reflection namespace. .NET reflection is a powerful mechanism which not
only allows you to inspect type information but also allows you to invoke
methods on those types at runtime. Certain reflection APIs also allow creating
of assembly in memory dynamically and use it in your code. In this article we
will examine the basic and most commonly used features of reflection. Reflection
APIs can be used to develop applications like class browsers, add-ons for
development IDEs and inelegant editors.
Assemblies are the building blocks of any .NET
application. All functionality of .NET application is exposed via assemblies.
Assemblies form a unit of deployment and versioning. Assemblies contain modules
which in turn contain various types (classes, structures, enumerations etc.).
The first thing you should do while using reflection
classes is to include System.Reflection namespace.
Loading an assembly
Before obtaining any information about types contained in
an assembly we must first load the assembly.
Assembly myassembly = Assembly.LoadFrom("employee.dll");
This statement loads an assembly called employee.dll. You
can substitute your own path here. Assembly class has a static method called
LoadFrom that loads the specified assembly in memory. The method returns an
instance of assembly class itself.
obtaining details about types from the assembly
The next step is to obtain a list of various types
contained in the assembly.
Types mytypes = myassembly.GetTypes();
There are two methods to get type information . The
method GetTypes returns an array of System.Type objects. The method GetType
returns a type object having details of specified object. Note that in our
example Company is the namespace. In case your assembly do not contain any
namespace you will simply write the type name.
Obtaining type details
The Type class has following properties that gives details
about the type under consideration :
Name : Gives name of the type
FullName : Give fully qualified name of the type
Namespace : Gives namespace name
IsCOMObject : Indicates if the type is a COM object
All the property names are self-explanatory and need no
obtaining details about methods, properties and fields
Each type may have fields (member variables), properties
and methods. The details about each of these types are obtained by following
methods of the Type object.
GetMembers() : Gives array of MemberInfo
GetFields() : Gives array of FieldInfo
GetProperties() : Gives array of PropertyInfo
GetMethods() : Gives array of MethodInfo
Note that you can also get information about specific
method, property or field using GetMethod("mymethod"), GetProperty("myprop") or
MethodInfo mymethods= mytype.GetMethods();
MethodInfo mymethod = mytype.GetMethod("GetSalary");
Following paragraphs list commonly used properties and
methods of above objects. The property and method names are self explanatory.
You can refer MSDN for more details.
Properties and methods of MethodInfo Object
Properties and methods of PropertyInfo Object
Properties and methods of FieldInfo Object
Invoking a method on a type
We have seen how to get information about various types
from an assembly. Reflection also allows us to create instances of these types
and invoke methods on them. Following code fragment shows just that.
object p=new object;
object p=new object;
Here, we first obtained type of employee class.
We then created an instance of it using Activator.CreateInstance()
method. There are two forms of Invoke() method :
If your method is not returning any value then you
may use following form
Invoke ( obj , obj)
If your method is returning some value and you want to
trap it use following form :
obj = Invoke ( obj , bindingflag,
binder , parameters, cultureflag )
For both the forms you pass instance of object on which
the method will be called and array of objects that contains
The second method shown here is with most commonly used
values for BindingFlags, Binder and Culture. For more detailed information on the second syntax of
Invoke method please refer MSDN.
Reflection allows a powerful mechanism to
introspect your types. The reflection APIs can be found in System.Reflection
namespace. The APIs allow you to inspect types as well as create types on the
fly and invoke methods on them.
Bipin Joshi is an author and IT trainer who writes about apparently unrelated topics - yoga & technology! Bipin has been programming since 1995 and is working with .NET framework ever since its inception. He is an internationally published author and has authored or co-authored more than half a dozen books and numerous articles on .NET technologies. Bipin was also a Microsoft MVP for six consecutive years. Bipin conducts professional training programs helping individuals learn Microsoft technologies better and faster. You can read more about him here. To know more about his training programs go here.
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