Page Load [RESOLVED]

[StrangerInBeijing]

I'm not sure if this is a question even worth asking here, but coming from Window's Forms apps, to Web applications is a bit strange....

I got a LoadBorderStyles method, that loop through all the members in the BorderStyle (TreeView) enumeration, convert each member to string and pop it into a listbox. Obviously I only want this method to run once.

Then I got a Treeview, and apply the borderstyle the user click in the listbox to the treeview (covert the sting back to enumeration member).

This all work fine, but each time I click a borderstyle, it is applied correctly, but the the LoadBorderStyles method, which I call from the Page_Load is excecuted again.

When I add the following line to the LoadBorderStyles method : lstBorderStyles.Items.Clear(); i get a "Object reference not set to an instance of an object" error

Here is my code

public partial class TestWhosTreeView17 : System.Web.UI.Page
{
  protected void Page_Load(object sender, EventArgs e)
  {
    myTreeView.TreeNodeSrc = "xml/treenode.xml";
    myTreeView.DataBind();

    myTreeView.Height = lstBorderStyles.Height;
    myTreeView.Width = lstBorderStyles.Width;

    LoadBorderStyles();

  }

  private void LoadBorderStyles()
  {

    lstBorderStyles.Items.Clear();
    //loop through all the borderstyle enumeration members, convert to
    //string and add to listbox
      foreach (string s in Enum.GetNames(typeof(System.Web.UI.WebControls.BorderStyle)))
      {
        lstBorderStyles.Items.Add(s);
    }
  }

  protected void lstBorderStyles_SelectedIndexChanged(object sender, EventArgs e)
  {
      //convert the selected item's text to a borderstyle enumeration member
      //apply the borderstyle member to the treeview's borderstyle property
      myTreeView.BorderStyle = (BorderStyle)Enum.Parse(typeof(BorderStyle), lstBorderStyles.SelectedItem.Text);
    
  }
}