public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
　　　　 // 自定义关机和logoff的事件
        Microsoft.Win32.SystemEvents.SessionEnding += SessionEndingEvent;
    }

    // 在此事件中决定是否关机或logoff
    private void SessionEndingEvent(object sender, SessionEndingEventArgs e)
    {
        SessionEndReasons endReasons = e.Reason;

        if (MessageBox.Show("Do you want to logoff or shutdown?", "is logoff or shutdown?", MessageBoxButtons.YesNo)
            == System.Windows.Forms.DialogResult.Yes)
        {
　　　　　　　// 会关机或logoff
            e.Cancel = false;
        }
        else
        {
        　　// 不会关机或logoff
            e.Cancel = true;
        }

        switch (endReasons)
        {
            case SessionEndReasons.Logoff:
                MessageBox.Show("logoff......");
                break;

            case SessionEndReasons.SystemShutdown:
                MessageBox.Show("shutdown......");
                break;

            default:
                break;
        }
    }
}