How to prevent or block closing a WinForms window?

Question

How can I prevent window closing by showing a MessageBox? (Technology:WinForms with C#)

When the close event occurs I want the

Answer 1

private void addFile_FormClosing( object sender, FormClosingEventArgs e ) {
var closeMsg = MessageBox.Show( "Do you really want to close?", "Warning", MessageBoxButtons.YesNo, MessageBoxIcon.Question );

if (closeMsg == DialogResult.Yes) {
    e.Cancel = false;
} else {
    e.Cancel = true;
}

e.Cancel is to enable or disable form closing event. For example, e.Cancel = true will disable you closing.