Question

When using the FormClosing event, why does the code e.Cancel = true; work, but new CancelEventArgs().Cancel = true; does not work?

private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
    e.Cancel = true;

    new CancelEventArgs().Cancel = true;
}

Answer 1

The event is raised by the Winforms plumbing code. The only way it can see that the custom event handler wants to alter the default behavior is through the e object. Creating a new CancelEventArgs object has no side-effects that the plumbing can detect.

There’s something else wrong, events are raised for the benefit of external code, letting it know what’s going on and giving it an option to alter behavior. There is no external code here, the event handler is actually part of the same class that raises the event. In other words, the form is listening to its own events. There’s a much better way to deal with that, you override the method that raises the event. Like this:

    protected override void OnFormClosing(FormClosingEventArgs e) {
        e.Cancel = true;
        base.OnFormClosing(e);
    }

Now external code can override the default behavior, events are raised after the OnXxxx method runs. And you have a choice, if you do not want the external code to override the behavior, simply swap the two statements.