วิธี Connect Database SQL Server 2008 ของ C# ผ่าน App.Config มือใหม่ขอความรู้หน่อยคับ

 private void button1_Click(object sender, EventArgs e) {
            string connectiongstring = null;
            SqlConnection cnn;
            connectiongstring = "Data Source=192.168.2.111;Initial Catalog=test;Persist Security Info=True;integrated security=SSPI";
            cnn =new SqlConnection(connectiongstring);
            try
            {
                cnn.Open();
                MessageBox.Show("Connection Open !","Connection Database");
                cnn.Close();
            }
            catch(Exception ex)
            {
                MessageBox.Show("Not Connection Open !","Connection Database");
            }

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
	<appSettings>
		<!-- Connection string -->
		<add key="SqlConnectionString" value="PWD=;UID=sa;Data Source=192.168.0.105;Provider=SQLOLEDB;Initial Catalog=myDatabase" />

	</appSettings>
</configuration>

            SqlConnection cnn;
            string connectiongstring = ConfigurationSettings.AppSettings["SqlConnectionString"];
            cnn = new SqlConnection(connectiongstring);