Silverlight and RX: Why I have to resize the Browser to update the UI?

Silverlight and RX: Why I have to resize the Browser to update the UI?

Let's start from the beginning:

I'm writing an algorithm for a Silverlight application, which has to do go through a lot different combinations of a high complexity to find an optimum. To give the algorithm the possibility to use all given resources on the client, I decided to do provide a parallel version.

Firstly I wrote my own async event-orientated scheduler class with a wait handle and a blocking object to limit the amount of parallel threads and to wait for all threads at the end, until I fired the final CalculationCompletedEvent (by the way: I was using Backgroundworkers to perform the multithreading). But something there wasn't thread safe, and the amount of returning elements in the result list wasn't constant. I considered not to spend more time in searching for the leak after a colleague pointed me on the Reactive Extensions (rx).

To get an idea of how to use this, I combined an consumer-producer example with some advices on how to use rx (example1 and example2).

This works great, but what I don't understand is: Why do I have to resize the browser to have the listbox updated and show the containing elements of "_receivedStrings"? Once again a tiny stupid neglect?

By the way: If you wouldn't recommend using the rx, give a shot and tell me why and what to use else.

XAML:

<UserControl x:Class="ReactiveTest.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"     mc:Ignorable="d"     d:DesignHeight="300" d:DesignWidth="400">      <Grid x:Name="LayoutRoot" Background="White">         <Grid.RowDefinitions>             <RowDefinition/>             <RowDefinition Height="Auto"/>         </Grid.RowDefinitions>         <ListBox HorizontalAlignment="Stretch" Name="listBox1"                   VerticalAlignment="Stretch" ItemsSource="{Binding}"/>         <Button Grid.Row="1" Content="Klick me!" Width="Auto" Height="Auto"                  HorizontalAlignment="Center" Click="Button_Click"/>     </Grid> </UserControl> 

Codebehind:

using System; using System.Collections.Generic; using System.Linq; using System.Net; using System.Windows; using System.Windows.Controls; using System.Windows.Documents; using System.Windows.Input; using System.Windows.Media; using System.Windows.Media.Animation; using System.Windows.Shapes; using System.IO; using System.Reactive.Linq;  namespace ReactiveTest {     public partial class MainPage : UserControl     {         private int _parallelThreadsAmount;          public IList<String> receivedStrings;          public MainPage()         {             InitializeComponent();             receivedStrings =                  new List<String>();             this._parallelThreadsAmount = 10;              this.listBox1.DataContext = receivedStrings;         }          private void Button_Click(object sender, RoutedEventArgs e)         {             IList<IObservable<String>> obsCollection =                  new List<IObservable<String>>();              foreach (var item in forums)             {                 obsCollection.Add(Calculate(item));             }             DateTime start = DateTime.Now;              obsCollection.Merge(this._parallelThreadsAmount)                 .Subscribe(                     y =>                     {                         receivedStrings.Add(                             String.Format("{0} - Received: {1}", receivedStrings.Count, y));                     },                     () =>                     {                         DateTime end = DateTime.Now;                         TimeSpan elapsed = end - start;                         this.receivedStrings.Add(                             String.Format(                                 "{0}/{1} done in {2} ms.",                                  receivedStrings.Count,                                  forums.Count(),                                  elapsed.TotalSeconds)                             );                     }                 );         }          IObservable<String> Calculate(String source)         {             Random rand = new Random();             return Observable.Defer(() => Observable.Start(() =>             {                 // simulate some work, taking different time,                  // to get the threads end in an other order than they've been started                                 System.Threading.Thread.Sleep(rand.Next(500, 2000));                 return source;             }));         }           static readonly String[] forums = new string[]         {             "announce",             "whatforum",             "reportabug",             "suggest",             "Offtopic",             "msdnsandbox",             "netfxsetup",             "netfxbcl",             "wpf",             "regexp",             "msbuild",             "netfxjscript",             "clr",             "netfxtoolsdev",             "asmxandxml",             "netfx64bit",             "netfxremoting",             "netfxnetcom",             "MEFramework",             "ncl",             "wcf",             "Geneva",             "MSWinWebChart",             "dublin",             "oslo",             // … some more elements         };     } } 

Answers & Comments...

Answer: 1

Ignoreing the lack of MVVM, IoC, Testability etc... You dont implement INotifyPropertyChanged, you are not using ObservableCollection(of T). 1. Change your public field to a pubilc readonly property 2. Use ObservableCollection instead of IList

//public IList<String> receivedStrings;  private readonly ObservableCollection<string> _receivedStrings = new ObservableCollection<string>(); public ObservableCollection<string> ReceivedStrings {     get { return _receivedStrings;} } 

you may also have to use the ObserveOnDispatcher() to ensure that you are called back on the Dispatcher, as you cant update the UI (even via Binding) on a thread that is not the Dispatcher's thread.

obsCollection.Merge(this._parallelThreadsAmount)                    .ObserveOn(Scheduler.Dispatcher)   //-or-.ObserveOnDispatcher()   //-or even better -.ObserveOn(_schedulerProvider.Dispatcher)   .Subscribe( 

by : Lee Campbellhttp://stackoverflow.com/users/393615

Answer: 2

Somehow I'm tempted to say that you are a bit confused with Rx, which is quite normal to be honest :)

As Lee Campbell writes there is a few things for starters, the resizing issue is not related to Rx at all as I see it but it's the ObservableCollection stuff.

Besides that I have modified your code a bit to handle some of the things I see, I'm not sure if it is exactly what you want since you have a specific assignment of how parallel you want stuff, but I'm gonna be bold and say it's not your concern (and hopefully I'm not being a smartass here).

private void Button_Click(object sender, RoutedEventArgs e) {     //extension method in Rx for wrapping     var obsCollection = forums.ToObservable();      //Observing on the dispatcher to prevent x-thread exceptions     obsCollection.Select( Calculate ).ObserverOnDispatcher().Subscribe(         receivedString => {                  receivedStrings.Add( String.Format("{0} - Received: {1}", receivedStrings.Count, y) );             },             ()=>{                 DateTime end = DateTime.Now;                 TimeSpan elapsed = end - start;                 this.receivedStrings.Add(                     String.Format( "{0}/{1} done in {2} ms.", receivedStrings.Count, forums.Count(), elapsed.TotalSeconds)                 );             }     ); }  Random rand = new Random(); IObservable<string> Calculate(string inputString) {     //launching the "calculation" on the taskpool...can be changed to other schedulers     return Observable.Start(         ()=>{             Thread.Sleep(rand.Next(150,250));              return inputString;             }, Scheduler.ThreadPool         ); } 

by : cyberzedhttp://stackoverflow.com/users/94302

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