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The Role of System.EventArgs and System.EventHandler

System.EventHandler is one of many delegate types used within the Windows Forms (and ASP.NET)

APIs during the event-handling process. As you have seen, this delegate can only point to methods

where the first argument is of type System.Object, which is a reference to the type that sent the

event. For example, if we were to update the implementation of the mnuFileExit_Click() method

as follows:

private void mnuFileExit_Click(object sender, EventArgs e)

{

MessageBox.Show(string.Format("{0} sent this event", sender.ToString()));

Application.Exit();

}

we would be able to verify that the mnuFileExit type sent the event, as the string

"E&xit sent this event"

is displayed within the message box. You may be wondering what purpose the second argument,

System.EventArgs, serves. In reality, the System.EventArgs type brings little to the table, as it simply

extends Object and provides practically nothing by way of addition functionality:

public class EventArgs

{

public static readonly EventArgs Empty;

static EventArgs();

public EventArgs();

}

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