Question

Tell me pls how to implement automatically loadable listBox. When scrolling down elements should be added to the previous one. Unfortunately the examples of such list I have not found, I saw that in the network are advised to use ObservalableCollection, but I don’t understand how to add elements to the collection. Here is my ample test application.

I need to connect to web-service and coming from the xml parsing. Here an example of work with Web service if request like this http://beta.sztls.ru/mapp/eps/?count=10 the service constructs xml with the latest ten news, on such a request http://beta.sztls.ru/mapp/eps/?count=10&skip=10, it returns the xml with the following ten news
I have a class

public class Item
    {
        public string Description { get; set; }
        public string Title { get; set; }
        public string Image { get; set; }
    }

And in code-behind

public partial class MainPage : PhoneApplicationPage
    {
        private ObservableCollection<Item> _collection;
        public ObservableCollection<Item> Collection
        {
            get
            {
                if (_collection == null)
                {
                    _collection = new ObservableCollection<Item>();
                }
                return _collection;
            }
        }

        private int endIndex = 0;

        // Конструктор
        public MainPage()
        {
            InitializeComponent();
            this._collection = new ObservableCollection<Item>();

            this.listBox1.ItemsSource = Collection;
            this.listBox1.Loaded += new RoutedEventHandler(listBox1_Loaded);

        }

        void listBox1_Loaded(object sender, RoutedEventArgs e)
        {
            try
            {
                LoadItems(10);
            }
            catch (Exception exception)
            {
                MessageBox.Show(exception.StackTrace);

            }
        }

        private void LoadItems(int count)
        {
            WebClient webClient = new WebClient();
            webClient.DownloadStringCompleted += new DownloadStringCompletedEventHandler(webClient_DownloadStringCompleted);
            webClient.DownloadStringAsync(
                new Uri(String.Format("http://beta.sztls.ru/mapp/eps/" + "?count={0}" + "&skip={1}" + "&ticks={2}",
                                      count, this.endIndex, DateTime.Now.Ticks)));
                 this.endIndex+=count
        }

        void webClient_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
        {
            if (e.Error == null)
            {
                ParseResult(e.Result);
            }
        }

        private void ParseResult(string result)
        {
            XElement element = XElement.Parse(result);



            var res = from part in element.Descendants("news")
                      select new Item
                                 {
                                     Image = part.Element("image_url").Value,
                                     Title = part.Element("title").Value,
                                     Description = part.Element("description").Value
                                 };

           //Here,as far as I understand, I need like this Collection.Add(res)
        }
    }

in Xaml

<toolkit:LongListSelector Grid.Row="1" IsFlatList="True" x:Name="listBox1">
                <toolkit:LongListSelector.ItemTemplate>
                    <DataTemplate>
                        <StackPanel Orientation="Horizontal">
                        <Image Source="{Binding Image}" Width="100" Height="100"/>
                            <StackPanel>
                                <TextBlock Text="{Binding Title}" FontSize="22" Foreground="Red"/>
                                <TextBlock Text="{Binding Decription}" FontSize="26" Foreground="Blue"/>
                            </StackPanel>
                        </StackPanel>
                    </DataTemplate>

                </toolkit:LongListSelector.ItemTemplate>
                <toolkit:LongListSelector.ListFooterTemplate>
                    <DataTemplate>
                        <TextBlock x:Name="footer"/>
                    </DataTemplate>
                </toolkit:LongListSelector.ListFooterTemplate>
            </toolkit:LongListSelector>

And how do I keep track of the time when I should send a request for load new items?

Thanks in advance for your help and sorry for my English. I have used http://www.bing.com/translator =)

Answer 1

Alright. If I understood everything correctly, you want to generate a collection of items from the xml file.
I suppose, the best option for you is to create an entity class with the fields “Image”, “Title”, “Description” e.t.c.(you’ve already done it) and in your ParseResult() method create a collection of this Entity. It will look like:

List<Entity> list = ParseResult(xdoc);

where in ParseResult you get the data from xml file with some expression, like:

return (from node in xdoc.Descendants("something") select new Entity(node.Attribute("Title").Value, node.Attribute("Image").Value,... ).ToList();

Now you’ll have a collection of items. What do you want to do with them next? I suppose, create a UI, using it. I suppose, there would be some controls, which are generated using this collection. So, if you want to update this page and add some new controls, you should check, which ones are already added to the page. In this case I would prefer to create a field in user control, which would check this. It should be unique, so let’s make it “title”.(it seems that “title” is unique in these documents) So, when you want to add a control on your page, you should check if none of the controls has the same “title” as the one, you want to add.

Hope, I understood all correct.

---

Alexandr, you just need a constructor for your item entity, like

public Item(string desc, string title, string image)
        {
            this.Description = desc;
            this.Title = title;
            this.Image = image;
        }

Then you could fill the list much easier:

List<Item> list = (from node in xdoc.Descendants("news") select new Item(node.Element("description").Value, node.Element("title").Value, node.Element("image_url").Value)).ToList();

That should work.