自由手記

 private void button1_Click(object sender, EventArgs e)
        {
            uint flags = 0x0;

            var isNetworkAvailable = InternetGetConnectedState(ref flags, 0);
            label1.Text = string.Format("Network available: {0} ({1})", isNetworkAvailable.ToString(), flags.ToString());
            
        }

        [DllImport("wininet")]
        public static extern bool InternetGetConnectedState(
            ref uint lpdwFlags,
            uint dwReserved
            );