Runtime Type Information (Reflection) in VB.NET
In this article I will explain you about Runtime Type Information (Reflection) in VB.NET.
Reflection is the sole mechanism of discovering class information at runtime. You can create instances of classes on the fly at runtime using Reflection namespace members.
The ability to list a type's members is a great way to quickly discover which elements are available. It is an important tool for reporting on your system as well as assisting in the development of user documentation. Using the Reflection namespace, you can control what kind of members you want to show to your users, as well as other information (such as the visibility of a particular method). You can also get information on all of the members in a class or specify only certain subsets (such as methods or fields). Also you can use this neat feature when documenting class hierarchy.
Example of Reflection
' example object creation factory
Imports System.Reflection
' simple class
Class [MyClass]
Public Shared x As Integer = 0
Public Sub prompt(ByVal param1 As String)
Console.WriteLine("MyClass… " & param1)
End Sub
Public Shared Sub prompt2()
Console.WriteLine("Here is a message from prompt2.")
End Sub
End Class
Class TheApp
Shared Sub Main()
' create the Type object
Dim type1 As Type = GetType([MyClass])
'or
' Type type1 = Type.GetType("MyClass");
' create an instance of that type
Dim o As [Object] = Activator.CreateInstance(type1)
DirectCast(o, [MyClass]).prompt("hello1")
' declare and populate the arrays to hold the information...
Dim fi As FieldInfo() = type1.GetFields(BindingFlags.[Default] Or BindingFlags.[Static] Or BindingFlags.NonPublic Or BindingFlags.[Public])
' fields
Dim mi As MethodInfo() = type1.GetMethods(BindingFlags.[Default] Or BindingFlags.[Static] Or BindingFlags.NonPublic Or BindingFlags.[Public])
' methods
' iterate through all the method members
For Each m As MethodInfo In mi
Console.WriteLine(m)
Next
' iterate through all the field members
For Each f As FieldInfo In fi
Console.WriteLine(f)
Next
Dim argValues As Object() = New Object() {"Hello2"}
Dim argNames As [String]() = New [String]() {"param1"}
' call the requested method with filled parameters
type1.InvokeMember("prompt", BindingFlags.[Default] Or BindingFlags.InvokeMethod, Nothing, o, argValues, Nothing, _
Nothing, argNames)
Console.ReadLine()
End Sub
End Class
Screen Output Generated from the above example is:
The reflection mechanism is also useful when developing applications that use third-party COM+ components at your site or in the market because you can use Reflection to accomplish late binding to COM objects via the IDispatch interface.
Conclusion
Hope this article would have helped you in understanding Runtime Type Information (Reflection) in VB.NET.