monodroid CustomAdapter NotifyDataSetChanged not working
===

My problem is. ((BaseAdapter)listAdapter).NotifyDataSetChanged(); doesn't work. 
what would be a problem?

[Activity (Label = "SportNews")]			
	public class SportNews : Activity
	{
		RssFeedItemAdapter listAdapter;
		JavaList<FeedItem> items = new JavaList<FeedItem>();
		protected override void OnCreate (Bundle bundle)
		{
			base.OnCreate (bundle);
			
			SetContentView(Resource.Layout.list_view);
			
			items = RssHelper.Instance.SportNews();
			
			//ListAdapter = new ArrayAdapter<string> (this, Resource.Layout.list_item, items);
			listAdapter = new RssFeedItemAdapter(this,items);
			
			ListView listView = FindViewById<ListView>(Resource.Id.listView);
			
			listView.Adapter = listAdapter;
			
			((BaseAdapter)listAdapter).NotifyDataSetChanged();
    		
    		listView.ItemClick += new EventHandler<AdapterView.ItemClickEventArgs>(listView_ItemClick);
			
			Timer timer = new Timer(PushNews, null, TimeSpan.Zero, TimeSpan.FromMinutes(15)); // get time from user preferences...
		}
		private void PushNews(object state)
		{
			items = RssHelper.Instance.SportNews();
			JavaList<FeedItem> feeds = new JavaList<FeedItem>();
			feeds.Add(new FeedItem()
			{
			 NewsPicture = "http://www.website.com/pic/test.jpg",
			 NewsTitle = "Test news",
			 NewsUrl = "http://www.google.com",
			});
			listAdapter = new RssFeedItemAdapter(this,feeds);
			((BaseAdapter)this.listAdapter).NotifyDataSetChanged();
		}
		
		void listView_ItemClick(object sender, Android.Widget.AdapterView.ItemClickEventArgs e)
		{
			//Get our item from the list adapter
			var item = this.listAdapter.GetItemAtPosition(e.Position);

			var intent = new Intent();
            intent.SetClass(this, typeof(NewsView));
            intent.PutExtra("Url", item.NewsUrl);
            StartActivity(intent);
		}
	}