Those two parameters (or variants of) are sent, by convention, with all events.
sender
: The object which has raised the event
e
an instance of EventArgs
including, in many cases, an object which inherits from EventArgs
. Contains additional information about the event, and sometimes provides ability for code handling the event to alter the event somehow.
In the case of the events you mentioned, neither parameter is particularly useful. The is only ever one page raising the events, and the EventArgs
are Empty
as there is no further information about the event.
Looking at the 2 parameters separately, here are some examples where they are useful.
sender
Say you have multiple buttons on a form. These buttons could contain a Tag
describing what clicking them should do. You could handle all the Click
events with the same handler, and depending on the sender
do something different
private void HandleButtonClick(object sender, EventArgs e)
{
Button btn = (Button)sender;
if(btn.Tag == "Hello")
MessageBox.Show("Hello")
else if(btn.Tag == "Goodbye")
Application.Exit();
// etc.
}
Disclaimer : That's a contrived example; don't do that!
e
Some events are cancelable. They send CancelEventArgs
instead of EventArgs
. This object adds a simple boolean property Cancel
on the event args. Code handling this event can cancel the event:
private void HandleCancellableEvent(object sender, CancelEventArgs e)
{
if(/* some condition*/)
{
// Cancel this event
e.Cancel = true;
}
}