Object reference not set to an instance of an object. when binding datatable to datagridview in c #

I Want to save multiple value from window form to datatable and then i bind this table to Datagridview. Value are adding in Datatable but At:

dataGridViewX1.DataSource = dt.DefaultView.Table);

binding point error shows

Object reference not set to an instance of an object

How Can I solve it?

public AddOrder(string ItemName,int Qty,Double Price)
    {


        try
        {
            DataTable dt = new DataTable();
            dt.Columns.Add("id");
            dt.Columns.Add("Item Name");

            dt.Columns.Add("Qty");
            dt.Columns.Add("Unit Price");
            dt.Columns.Add("Amounts");


            DataRow dr = dt.NewRow();
            dr["id"] = a;
            a++;

            dr["Item Name"] = ItemName;
            dr["Qty"] = Qty;
            dr["Unit Price"] = Price;
            dr["Amounts"] = (Convert.ToInt32(dr["Qty"]) * Convert.ToInt32(dr["Unit Price"]));
            dt.Rows.Add(dr);

            dataGridViewX1.DataSource = dt.DefaultView.Table;

        }
        catch(Exception ee)
        {
            DevComponents.DotNetBar.MessageBoxEx.Show(ee.Message,"Error Message");
        }
    }