filling girdview on the bases of dropdownlist

 dbcon obj = new dbcon();
    protected void Page_Load(object sender, EventArgs e)
    {
        //dbcon obj = new dbcon();
        if (!IsPostBack)
        {
            string querydr = "select * from ESK_Categories";
            SqlDataReader dr = obj.fillcomb(querydr);
            DropDownList1.DataSource = dr;
            DropDownList1.DataValueField = "CategoryName";
            DropDownList1.DataBind();



        }
        if (!IsPostBack)
        {
            bind();
        }

    }
    public void bind()
    {
        string query = "SELECT ESK_Products.ProductID, ESKProducts.ProductName,ESK_Products.UnitCost ,ESK_Cateogries.CategoryName FROM ESK_Products LEFT JOIN ESK_Categories ON ESK_Products.ProductsID=ESK_Categories.CategoryID Where CategoryName='" + DropDownList1.Text + "'";  
        DataSet ds = obj.fillgrid(query);
        GridView1.DataSource = ds.Tables[0];
        GridView1.DataBind();
    }
}