public partial class TwitterSearchViewModel : INotifyPropertyChanged
{
  private TweetViewModelCollection _tweets = new TweetViewModelCollection();
 
  private IMarshalInvoke _marshalInvoke;
 
  private string _searchText = "WinRT";
 
  public TwitterSearchViewModel(IMarshalInvoke marshalInvoke)
  {
    _marshalInvoke = marshalInvoke;
  }
 
  /// <summary>
  /// Gets / sets the search term
  /// </summary>
  public string SearchText
  {
    get {  return _searchText;  }
    set
    {
      _searchText = value;
      OnPropertyChanged("SearchText");
    }
  }
 
  /// <summary>
  /// Gets the search results
  /// </summary>
  public TweetViewModelCollection Tweets
  {
    get { return _tweets; }
    set { _tweets = value; }
  }
 
  /// <summary>
  /// Gets a command that executes the search
  /// </summary>
  public ICommand ExecuteSearchCommand
  {
    get
    {
      return new DelegateCommand(() => ExecuteSearch());
    }
  }
}

#if WINRT
 
using Windows.UI.Xaml.Input;
 
#else
 
using System.Windows.Input;
 
#endif

#if WINRT
 
// used for ICommand
using Windows.UI.Xaml.Input;
 
// used for INotifyPropertyChanged
using Windows.UI.Xaml.Data;
 
#else
 
using System.ComponentModel;
using System.Windows.Input;
 
#endif

/// <summary>
/// Parses the response from our twitter request, creating a list of TweetViewModel instances
/// </summary>
private void ParseXMLResponse(string xml)
{
  var doc = XDocument.Parse(xml);
  var items = doc.Descendants(AtomConst.Entry)
                  .Select(entryElement => new TweetViewModel()
                  {
                    Title = entryElement.Descendants(AtomConst.Title).Single().Value,
                    Id = long.Parse(entryElement.Descendants(AtomConst.ID).Single().Value.Split(':')[2]),
                    ProfileImageUrl =  entryElement.Descendants(AtomConst.Link).Skip(1).First().Attribute("href").Value,
                    Timestamp = DateTime.Parse(entryElement.Descendants(AtomConst.Published).Single().Value),
                    Author = entryElement.Descendants(AtomConst.Name).Single().Value
                  });
 
  _tweets.Clear();
  foreach (var item in items)
  {
    _tweets.Add(item);
  }
}
 
/// <summary>
/// Searches for the given term
/// </summary>
private void ExecuteSearch()
{
  IsSearching = true;
 
  // perform the search
  string uri = _twitterUrl + SearchText;
  HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(new Uri(uri));
  request.BeginGetResponse(new AsyncCallback(ReadCallback), request);
}
 
/// <summary>
/// A callback that receives the search results
/// </summary>
private void ReadCallback(IAsyncResult asynchronousResult)
{
  HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
  HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asynchronousResult);
  using (StreamReader streamReader1 = new StreamReader(response.GetResponseStream()))
  {
    string resultString = streamReader1.ReadToEnd();
 
    // marshall onto the UI thread and parse
    _marshalInvoke.Invoke(() =>
      {
        Tweets.Clear();
        ParseXMLResponse(resultString);
        IsSearching = false;
      });
  }
}

#if WINRT
 
// used for ICommand
using Windows.UI.Xaml.Input;
 
#else
 
using System.Windows.Input;
 
#endif
 
namespace SLUGUK.ViewModel
{
  public class DelegateCommand : ICommand
  {
    private Action _action;
 
    public DelegateCommand(Action action)
    {
      _action = action;
    }
 
    public bool CanExecute(object parameter)
    {
      return true;
    }
 
#if WINRT
    public event Windows.UI.Xaml.EventHandler CanExecuteChanged;
#else
    public event EventHandler CanExecuteChanged;
#endif
 
    public void Execute(object parameter)
    {
      _action();
    }
  }
}

<UserControl x:Class="WinRTMetroTwitter.View.TwitterSearchView"
    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:local="using:WinRTMetroTwitter.View"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">
 
    <UserControl.Resources>
        <local:BoolToVisibilityConverter x:Key="BoolToVisibilityConverter"/>
        <local:ImageConverter x:Key="ImageConverter"/>        
    </UserControl.Resources>
 
    <Grid x:Name="LayoutRoot" Background="#FF0C0C0C">
        <Grid Margin="50"
              Width="400"
              HorizontalAlignment="Left">
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition Height="*"/>
            </Grid.RowDefinitions>
            <StackPanel Orientation="Horizontal">
                <TextBox Text="{Binding Path=SearchText, Mode=TwoWay}"
                     Width="200"/>
                <Button Command="{Binding Path=ExecuteSearchCommand}"
                    Content="Go!"/>
                <TextBlock VerticalAlignment="Center"
                     Visibility="{Binding Path=IsSearching, Converter={StaticResource BoolToVisibilityConverter}}"
                     Text="Searching ..."
                     Margin="20,0,0,0"
                     FontSize="15"/>
            </StackPanel>
 
            <!-- renders the search results -->
            <ItemsControl x:Name="itemsControl"
                          Grid.Row="2">
                <ItemsControl.ItemsPanel>
                    <ItemsPanelTemplate>
                        <StackPanel Orientation="Vertical"/>
                    </ItemsPanelTemplate>
                </ItemsControl.ItemsPanel>
                <ItemsControl.ItemTemplate>
                    <DataTemplate>
                        <StackPanel Orientation="Horizontal"
                                    Margin="5">
                           <Image Source="{Binding ProfileImageUrl, Converter={StaticResource ImageConverter}}"
                                  Width="96" Height="96"
                                  Stretch="UniformToFill"
                                  Margin="2"
                                  VerticalAlignment="Top"/>
 
                            <StackPanel Orientation="Vertical">
                                <TextBlock Text="{Binding Title}"
                                           TextWrapping="Wrap"
                                           FontSize="15"
                                           Width="300"
                                           HorizontalAlignment="Left"/>
                                <StackPanel Orientation="Horizontal">
 
                                    <TextBlock FontWeight="Bold"
                                               Text="{Binding Path=Author}"
                                               FontSize="15"/>
 
                                    <TextBlock Margin="10,0,0,0"
                                              Text="{Binding Path=Timestamp}"
                                               FontSize="15"
                                              Foreground="#333"/>
                                </StackPanel>
                            </StackPanel>
                        </StackPanel>
                    </DataTemplate>
                </ItemsControl.ItemTemplate>
            </ItemsControl>
 
            <Rectangle Fill="#FF0C0C0C"
                   Opacity="0.5"
                   Grid.Row="1"
                   Visibility="{Binding Path=IsSearching, Converter={StaticResource BoolToVisibilityConverter}}"/>
        </Grid>
    </Grid>
</UserControl>

namespace WinRTMetroTwitter.View
{
  public class BoolToVisibilityConverter : IValueConverter
  {
    public object Convert(object value, string typeName, object parameter, string language)
    {
      return (bool)value ? Visibility.Visible : Visibility.Collapsed;
    }
 
    public object ConvertBack(object value, string typeName, object parameter, string language)
    {
      throw new NotImplementedException();
    }
  }
}

public sealed partial class TwitterSearchView : UserControl
{
  private TwitterSearchViewModel feedViewModel;
 
  public TwitterSearchView()
  {
    InitializeComponent();
 
    this.Loaded += ResultsView_Loaded;
  }
 
  private void ResultsView_Loaded(object sender, RoutedEventArgs e)
  { 
    feedViewModel = this.DataContext as TwitterSearchViewModel;
 
    // detect collection changed
    feedViewModel.Tweets.CollectionChanged += FeedItems_CollectionChanged;
  }
 
 
  private void FeedItems_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
  {
    // manually 'refresh' the UI
    itemsControl.ItemsSource = null;
    itemsControl.ItemsSource = feedViewModel.Tweets;
  }
}