Reflection makes it easy to invoke a method (or assign a field or a
property) by its name. For example, suppose you have the following classes:
Class Person
Event PropertyChanged(ByVal propertyName As String, ByVal newValue As Object)
Dim m_Name As String
Property Name() As String
Get
Return m_Name
End Get
Set(ByVal Value As String)
If Value <> m_Name Then
m_Name = Value
RaiseEvent PropertyChanged("Name", m_Name)
End If
End Set
End Property
End Class
Here's how you can assign a Person's Name and a Car's Color through
reflection:
' this code assumes the following statement
' Imports System.Reflection
' create a Person object
Dim pe As New Person()
' note how you can create the array of arguments on the fly
pe.GetType.InvokeMember("Name", BindingFlags.SetProperty, Nothing, pe, _
New Object() {"John"})
However, setting up an event handler for an event of which you know just the
name isn't as immediate. These are the steps you need to follow:
1. Create an event handler that reflects the event syntax
2. Get the EventInfo object corresponding to the event in question
3. Create a delegate to local event handler by means of the Delegate.CreateDelegate method
4. call the EventInfo.AddEventHandler method to establish the connection
Remember to remove the event handler when you don't need to receive events
any longer. Here's a complete example that uses the Person class, but it can
be easily adapted to other classes:
Module MainModule
Sub Main
' create a Person object
Dim pe As New Person()
' get a reference to the EventInfo for this object
Dim peEv As EventInfo = pe.GetType.GetEvent("PropertyChanged")
' create a delegate to the local procedure
Dim peDel As [Delegate] = [Delegate].CreateDelegate(peEv.EventHandlerType, _
Me, "PropertyChanged")
' make the local procedure a handler for the event
peEv.AddEventHandler(pe, peDel)
' prove that it works
pe.Name = "John"
' (always remove event handlers)
peEv.RemoveEventHandler(pe, peDel)
End Sub
Private Sub PropertyChanged(ByVal propertyName As String, _
ByVal newValue As Object)
Console.WriteLine("Property {0} has changed. The new value is {1}", _
propertyName, newValue)
End Sub
End Module