Binaryworld - Set up event handlers through reflection ... [ VB.net -> Classes & Objects ]

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:

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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:

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' 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:

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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