Objective C: what is a “(id) sender”?

Question

In some IBAction I saw:

- (IBAction)pushButton:(id)sender;

This (id)sender when do I use it?

Answer 1

(id)sender is the object which sent the message to that selector.

Code example:

- (IBAction)submitButton:(id)sender {
    UIButton *button = (UIButton *)sender;
    [button setEnabled:NO];
    [button setTitle:@"foo" forState:UIControlStateDisabled];
}