currencymanager AddNew（）方法c＃

Question

我正在尝试使用currencymanager addnew方法向我的数据库添加新记录，但它没有更新数据库，这里是完整的代码。

namespace currencyManager
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        SqlConnection con;
        SqlCommand cmd;
        SqlDataAdapter da;
        DataTable dt;
        CurrencyManager cm;

        private void Form1_Load(object sender, EventArgs e)
        {
            con = new SqlConnection("data source=COUNTER16-PC,initial catalog=myDatabase;integrated security=true");
            con.Open();
            cmd = new SqlCommand("Select * from Students", con);
            da = new SqlDataAdapter();
            da.SelectCommand = cmd;
            dt = new DataTable();
            da.Fill(dt);
            cm = (CurrencyManager)BindingContext[dt];
            txtID.DataBindings.Add("text",dt,"ID");
            txtFname.DataBindings.Add("text", dt, "FirstName");
            txtLname.DataBindings.Add("text", dt, "LASTNAME");
            txtState.DataBindings.Add("text", dt, "STATE");
            txtPhone.DataBindings.Add("text", dt, "PHONE");
            txtEmail.DataBindings.Add("text", dt, "EMAIL");
            txtGrade.DataBindings.Add("text", dt, "GRADEYEAR");
            txtGrade.DataBindings.Add("text", dt, "GPA");
            txtProgram.DataBindings.Add("text", dt, "PROGRAM");
            txtNews.DataBindings.Add("text", dt, "NEWLETTER");

        }

        private void btn_first_Click(object sender, EventArgs e)
        {
            cm.Position = 0;
        }

        private void btn_prev_Click(object sender, EventArgs e)
        {
            cm.Position--;
        }

        private void btn_next_Click(object sender, EventArgs e)
        {
            cm.Position++;
        }

        private void btn_last_Click(object sender, EventArgs e)
        {
            cm.Position = cm.Count - 1;
        }

        private void btn_add_Click(object sender, EventArgs e)
        {
            cm.AddNew();
        }

        private void btn_save_Click(object sender, EventArgs e)
        {
            cm.EndCurrentEdit();
        }

        private void btn_update_Click(object sender, EventArgs e)
        {

        }

        private void btn_delete_Click(object sender, EventArgs e)
        {
            cm.RemoveAt(cm.Position);
        }
    }
}

提前谢谢