Reload Longlistselector in WP8

Question

I had about 6 Longlistselectors in my Panorama App for Wp8. And when the app start running, they load data from a XML file into 6 ObservableCollection list then apply it to longlistselector item source.(this working well)

I have a background worker method which is download data from the internet then update them to the XML file and then save it.

I tried many things, spent a lot of hours to reload that new info from XML to Longlistselector but failed :( Its seem like I cant reload XML after save it. Anyone can help me with this? Tks so much. If u need any code, just tell me, I will provide them all. Sry for my bad english.

private async void BwDoWork(object sender, DoWorkEventArgs e)
    {
        var xdoc = XDocument.Load("APPSDATA.xml");
        var listnode = from c in xdoc.Descendants("Ungdung") select c;
        var xElements = listnode as IList<XElement> ?? listnode.ToList();

        for (int i = 0; i < xElements.Count; i++)
        {
            var element = xElements[i].Element("Id");
            if (element != null)
            {
                var appId = element.Value;
                var appVersion = await GetAppsVersion(appId);
                xElements[i].SetElementValue("Version", appVersion.ToString());
            }
            if (i != xElements.Count - 1) continue;
            var file = new FileStream("APPSDATA.xml", FileMode.Open);
            xdoc.Save(file);                
        }
    }