asp.net listbox绑定问题

我一个页面里有添加，还有就是listbox,listbox我已经绑定好了, 就是我点击添加之后就是不会绑定到listbox里，要刷新之后才可以看的到我添加的内容，这是怎么一回事。代码如下：
public void bind()
{
string strCon = "PROVIDER=Microsoft.Jet.OLEDB.4.0;DATA Source=" + System.Web.HttpContext.Current.Server.MapPath("../database/data.mdb");
string sqlstr = "select distinct productname from proCategory";
OleDbConnection sqlcon = new OleDbConnection(strCon);
sqlcon.Open();
OleDbDataAdapter myda = new OleDbDataAdapter(sqlstr, sqlcon);
DataSet myds = new DataSet();

myda.Fill(myds, "proCategory");
this.ListBox1.DataSource = myds;
//this.ListBox1.DataKeyNames = new string[] { "id" };//主键
// this.ListBox1.DataBind();
// ListBox1.DataTextField = "productname";
// ListBox1.DataValueField = "id";
ListBox1.DataBind();
sqlcon.Close();
}
protected void Page_Load(object sender, EventArgs e)
{
if (!this.IsPostBack)
{
this.bind();
}

}