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

For prevent or block the form closing in particular situation you can use this strategy:

private void MyForm_FormClosing(object sender, FormClosingEventArgs e)
{

    if (FLAG_CONDITION == true)
    {
        MessageBox.Show("To exit save the change!!");
        e.Cancel = true;
    }

}