Silverlight 2 Beta 2 - Doing Data Part IV: Browser / Cookie Interaction

As you travel in your Silverlight oddysey, you will discover that there is often a need for persisting simple state and interacting with the underlying browser DOM. Fortunately, Silverlight's System.Windows.Browser namespace makes this easy. We create a Silverlight Twitter Search widget using the Twitter API. We'll save searches in a cookie, navigate to selected Tweets using the browser, and when the Back button is pressed, we'll recapture the last search via the cookie and redisplay it.

This app uses the Twitter REST API to perform a search and return RSS like so: 

http://search.twitter.com/search.rss?lang=en&rpp=100&q=searchterm

If you check  http://search.twitter.com/crossdomain.xml you'll see that our kind friends at Twitter are enabling cross-domain access for us.

When the Silverlight Page class initializes, I check for a cookie called "search". If it isn't null, I execute my asynchronous MakeRequest call which then databinds the ListBox that is used to show the results. When you click on a result, we grab the Url and use the System.Windows.Browser.HtmlPage.Window.Navigate method to make the browser - not the Silverlight app - request the selected page. Having saved the search in a cookie, when the user clicks their browser's Back button, our Silverlight app reads the cookie, and re-issues the request, redisplaying the results of the last search. If we wanted, we could actually use the retrieved cookie value to load the previous results from IsolatedStorage, a technique which I've covered in a previous article.  Since all of the business logic is included in the Page.Xaml.cs class, I present it here:

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Net;
using System.ServiceModel.Syndication;
using System.Text.RegularExpressions;
using System.Threading;
using System.Windows;
using System.Windows.Browser;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Xml;

namespace SLTwitterSearch
{
    public partial class Page : UserControl
    {
            SynchronizationContext uiThread;
            string searchUrl = "http://search.twitter.com/search.rss?lang=en&rpp=100&q=";

            public Page()
            {
                InitializeComponent();
                // Grab a reference to the UI thread
                uiThread = SynchronizationContext.Current;
                string cookval = GetCookie("search");
                if(cookval!=null)
                {
                    this.feedAddress.Text = cookval;
                    MakeRequest();

                }
            }

            private string GetCookie(string key)
            {
                string[] cookies = HtmlPage.Document.Cookies.Split(';');
                foreach (string cookie in cookies)
                {
                    string[] keyValue = cookie.Split('=');
                    if (keyValue.Length == 2)
                    {
                        if (keyValue[0].ToString() == key)
                            return keyValue[1];
                    }
                }
                return null;
            }

            private void Button_Click(object sender, RoutedEventArgs e)
            {
                itemsList.Visibility = Visibility.Collapsed;
                MakeRequest();
            }


        void MakeRequest ()
        {
             // save this search in a cookie for later retrieval
            this.SetCookie("search", feedAddress.Text);
            // Begin HTTP request to get feed
            HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(new Uri(searchUrl + feedAddress.Text));
            request.BeginGetResponse(new AsyncCallback(responseHandler), request);
        }

            void responseHandler(IAsyncResult asyncResult)
            {
                // Get HTTP response
                HttpWebRequest request = (HttpWebRequest)asyncResult.AsyncState;
                HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asyncResult);
                // Load feed into SyndicationFeed object
                XmlReader reader = XmlReader.Create(response.GetResponseStream());
                SyndicationFeed feed = SyndicationFeed.Load(reader);
                // invoke the databinding method on the UI thread
                uiThread.Post(setItemsListDataContext, feed);
            }

            void setItemsListDataContext(object feed)
            {
                // Set up databinding
                itemsList.DataContext = (feed as SyndicationFeed).Items;
                itemsList.Visibility = Visibility.Visible;
            }

            private void itemsList_SelectionChanged(object sender, SelectionChangedEventArgs e)
            {
                SyndicationItem itm = (sender as ListBox).SelectedItem as SyndicationItem;
               // Twitter puts the Url to the Tweet in the "Id" field:
               System.Windows.Browser.HtmlPage.Window.Navigate(new Uri(itm.Id.ToString()));
            }


        private void SetCookie(string key, string value)
        {    
            // Expire in 7 days   
            DateTime expireDate = DateTime.Now + TimeSpan.FromDays(7);   
            string newCookie = key + "=" + value + ";expires=" + expireDate.ToString("R");    
            HtmlPage.Document.SetProperty("cookie", newCookie);
        }

   }

    // Helper classes to clean up and shape received data for UI databinding
        public class HtmlSanitizer : IValueConverter
        {
            public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
            {
                // Remove HTML tags and empty newlines and spaces
                string returnString = Regex.Replace(value as string, "<.*?>", "");
                returnString = Regex.Replace(returnString, @"\n+\s+", "\n\n");
                // Decode HTML entities
                returnString = HttpUtility.HtmlDecode(returnString);
                return returnString;
            }

            public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
            {
                throw new NotImplementedException();
            }
        }

        public class LinkFormatter : IValueConverter
        {
            public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
            {
                // Get the first link - that's the link to the post
                return ((Collection)value)[0].Uri;
            }

            public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
            {
                throw new NotImplementedException();
            }
        }
    }