Question

While going through the checkBox I found there is written

CheckBox checkbox = (CheckBox)sender

on checkBox1_CheckedChanged event.

Please explain what it means?

Answer 1

The line simply casts sender to a CheckBox.

Why?

The event handler signature for the CheckedChanged event is:

CheckChanged(object sender, EventArgs e)

So, you need to cast sender back to a CheckBox if you want to use any CheckBox specific functionality – object doesn’t have much that you can use…

This way the checkbox variable can be used to get the checkbox Id and operate on the checkbox.