What are events?

As compared to delegates events works with source and listener methodology. So listeners who are interested in receiving some events they subscribe to the source. Once this subscription is done the source raises events to its entire listener when needed. One source can have multiple listeners.

In sample given below class "ClsWithEvents" is a event source class, which has a event "EventAddString()". Now the listeners who are interested in receiving this events they can subscribe to this event. In class "FrmWithEvents" you can see they handle clause which is associated with the "mobjClsWithEvents" objects.

Public Class ClsWithEvents
Event EventAddString(ByVal Value As String)
Public Sub AddString()
RaiseEvent EventAddString("String added by Event")
End Sub
End Class
Public Class FrmWithEvents
Inherits System.Windows.Forms.Form
Private WithEvents mobjClsWithEvents As New ClsWithEvents()
Private Sub FrmWithEvents_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
End Sub
Private Sub mobjClsWithEvents_EventAddString(ByVal Value As String) Handles mobjClsWithEvents.EventAddString
LstData.Items.Add(Value)
End Sub
Private Sub CmdRunEvents_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CmdRunEvents.Click
mobjClsWithEvents.AddString()
End Sub
End Class