tutorial pt. 2

IInfiniteScrollingItemsSource.cs

namespace InfiniteScroll
{
    public interface IInfiniteScrollingItemsSource
    {
        void GetMoreItems(int count = 10);

    }
}

MainPage.xaml

<UserControl x:Class="InfiniteScroll.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:clr="clr-namespace:InfiniteScroll"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="440">

    <Grid x:Name="LayoutRoot" Background="White" Loaded="LayoutRoot_Loaded">
        <clr:InfiniteScrollingListBox x:Name="ScrollingListBox" Width="400" Height="200" >
        </clr:InfiniteScrollingListBox>
    </Grid>
</UserControl>

MainPage.xaml.cs

using System.Windows;
using System.Windows.Controls;

namespace InfiniteScroll
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
        }

        private void LayoutRoot_Loaded(object sender, RoutedEventArgs e)
        {
            ScrollingListBox.ItemsSource = new ScrollingObservableItemsSource {Username = "notch"};
            ScrollingListBox.LoadItems();
        }
    }
}

ScrolllingObservableItemsSource.cs

using System;
using System.Linq;
using System.Net;
using System.Collections.ObjectModel;
using System.Xml.Linq;

namespace InfiniteScroll
{
    public class ScrollingObservableItemsSource : ObservableCollection<TumblrPost>, IInfiniteScrollingItemsSource
    {
        private const string BASE_URL = "http://{0}.tumblr.com/api/read";
        public string Username { get; set; }
        private WebClient _webClient;
        private bool _fetching = false;


        public ScrollingObservableItemsSource()
        {
            _webClient = new WebClient();
            _webClient.DownloadStringCompleted += _webClient_DownloadStringCompleted;
        }

        void _webClient_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
        {
            _fetching = false;
            // run xml through factory
            if (e.Error != null)
                throw e.Error;

            XDocument doc = XDocument.Parse(e.Result);
            var posts = from XElement elm in doc.Root.Element("posts").Elements()
                        where elm.Attribute("type").Value == "regular"
                         select new TumblrPost(elm.Element("regular-title"));

            foreach (var tumblrPost in posts)
            {
                if (!this.Any(x => x.Equals(tumblrPost)))
                {
                    Add(tumblrPost);   
                }
            }
        }

        public void GetMoreItems(int count)
        {
            if (_fetching) return;
            _webClient.DownloadStringAsync(MakeUrl(count,Count));
            _fetching = true;
        }

        private Uri MakeUrl(int count = 10,int start = 0)
        {
            UriBuilder builder = new UriBuilder(String.Format(BASE_URL,Username));
            builder.Query = "num=" + count.ToString();
            builder.Query += "&start=" + start.ToString();
            return builder.Uri;
        }
    }
}

TumblrPost.cs

using System.Xml.Linq;

namespace InfiniteScroll
{
    public class TumblrPost
    {
        public string Title { get; set; }

        public TumblrPost(XElement title)
        {
            if (title == null)
                Title = "No Title";
            else
                Title = title.Value;
        }

        public override string ToString()
        {
            return Title;
        }

        public bool Equals(TumblrPost other)
        {
            if (ReferenceEquals(null, other)) return false;
            if (ReferenceEquals(this, other)) return true;
            return Equals(other.Title, Title);
        }

        public override int GetHashCode()
        {
            return (Title != null ? Title.GetHashCode() : 0);
        }
    }
}