protected void btnAddRow_Click(object sender, EventArgs e)
    {
        DataTable dt = AddElement();
        DataRow dr;

        object[] rowArray = new object[2];
        for (int i = 0; i < 10; i++)
        {
            rowArray[0] = null;
            rowArray[1] = new TextBox();
            dr = dt.NewRow();
            dr.ItemArray = rowArray;
            dt.Rows.Add(dr);
        }
        
        gvTest.DataSource = dt;
        gvTest.DataBind();
    }
    private DataTable AddElement()
    {
        DataTable table = new DataTable("table");
        DataColumn idColumn = new DataColumn("id",
            Type.GetType("System.Int32"));
        idColumn.AutoIncrement = true;
        idColumn.AutoIncrementSeed = 10;
        table.Columns.Add(idColumn);
        DataColumn firstNameColumn = new DataColumn("Item");
        table.Columns.Add(firstNameColumn);
        return table;
    }