Semantic zoom – beyond the stock behaviour – #windev #winrt

Update: Download a sample implementation from skydrive

Last year I was working on Cineworld app for Windows 8. Having use LongListSelector I wanted to ensure that I can transfer the look and feel. However I was fighting multiple battles – the first one is that while LongListSelector is a single control, SemanticZoom control itself contains ZoomInView and ZoomedOutView. These are independent of each other and most examples then to show settings data to zoomed in view and then zoomed out view referring to zoomed in view. It gets messy – maybe I am just slow but it was not intuitive and took me ages.

While mucking around, I came across this post and from there, kept trying till I got what I wanted.

 

 

<Page.Resources>
    <CollectionViewSource x:Name="cvsFilms" IsSourceGrouped="true" />

    <!-- Zoomed out templates and selectors -->
    <DataTemplate x:Key="GroupTemplate">
        <Border Margin="6" Width="75" Height="75" Background="Black" >
            <TextBlock Text="{Binding Name}" Foreground="White" FontSize="32" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center" />
        </Border>
    </DataTemplate>
    <DataTemplate x:Key="EmptyGroupTemplate">
        <Border Margin="6" Width="75" Height="75" BorderBrush="Black" BorderThickness="1" Background="LightGray">
            <TextBlock Text="{Binding Name}" Foreground="Black" FontSize="32" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center" />
        </Border>
    </DataTemplate>
    <local:EmptyOrFullSelector
            x:Key="FilmGroupEmptyOrFullSelector"
            Empty="{StaticResource EmptyGroupTemplate}"
            Full="{StaticResource GroupTemplate}" />
    <DataTemplate x:Key="GroupHeaderTemplate">
        <Border Margin="20, 20, 0, 0" Width="75" Height="75" Background="Black" Tapped="Grid_Tapped">
            <TextBlock Text="{Binding Key}" Foreground="White" FontSize="32" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center" />
        </Border>
    </DataTemplate>
    <DataTemplate x:Key="GroupItemTemplate">
        <Border Margin="14, 20, 0, 0">
            <Grid Height="350" Width="185" Margin="0">
                <Grid.RowDefinitions>
                    <RowDefinition Height="Auto" />
                    <RowDefinition Height="*" />
                </Grid.RowDefinitions>
                <Image  Source="{Binding PosterUrl}" Height="278" Width="185" VerticalAlignment="Top" HorizontalAlignment="Left" Stretch="UniformToFill"/>
                <TextBlock Grid.Row="1" TextWrapping="Wrap" VerticalAlignment="Top" Text="{Binding Title}" HorizontalAlignment="Center" FontFamily="Segoe UI" />
            </Grid>
        </Border>
    </DataTemplate>
</Page.Resources>

<SemanticZoom x:Name="semanticZoom" Background="White" HorizontalAlignment="Stretch" Grid.Row="1" VerticalAlignment="Stretch">
    <SemanticZoom.ZoomedOutView>
        <GridView ScrollViewer.IsHorizontalScrollChainingEnabled="False" HorizontalAlignment="Center" ItemTemplateSelector="{StaticResource FilmGroupEmptyOrFullSelector}" >
            <GridView.ItemsPanel>
                <ItemsPanelTemplate>
                    <WrapGrid Background="LightGray" MaximumRowsOrColumns="9" VerticalChildrenAlignment="Center" Orientation="Horizontal"/>
                </ItemsPanelTemplate>
            </GridView.ItemsPanel>
        </GridView>
    </SemanticZoom.ZoomedOutView>
    <SemanticZoom.ZoomedInView>
        <GridView x:Name="gvZoomedInFilms" ItemsSource="{Binding Source={StaticResource cvsFilms}}" IsSwipeEnabled="True" ScrollViewer.IsHorizontalScrollChainingEnabled="False" ItemTemplate="{StaticResource GroupItemTemplate}">
            <GridView.ItemsPanel>
                <ItemsPanelTemplate>
                    <VirtualizingStackPanel Orientation="Horizontal"/>
                </ItemsPanelTemplate>
            </GridView.ItemsPanel>
            <GridView.GroupStyle>
                <GroupStyle HeaderTemplate="{StaticResource GroupHeaderTemplate}">
                    <GroupStyle.Panel>
                        <ItemsPanelTemplate>
                            <VariableSizedWrapGrid Orientation="Vertical" Margin="0,0,50,0"/>
                        </ItemsPanelTemplate>
                    </GroupStyle.Panel>
                </GroupStyle>
            </GridView.GroupStyle>
        </GridView>
    </SemanticZoom.ZoomedInView>
</SemanticZoom>

List<GroupInfoList<object>> dataLetter = null;

public ListFilms()
{
    this.InitializeComponent();

    FilmData cd = new FilmData(App.Films);

    dataLetter = cd.GroupsByLetter; 
    cvsFilms.Source = dataLetter;
    gvZoomedInFilms.SelectionChanged -= gvZoomedIn_SelectionChanged;
    gvZoomedInFilms.SelectedItem = null;
    (semanticZoom.ZoomedOutView as ListViewBase).ItemsSource = cd.FilmHeaders;     gvZoomedInFilms.SelectionChanged += gvZoomedIn_SelectionChanged;

    semanticZoom.ViewChangeStarted -= semanticZoom_ViewChangeStarted;
    semanticZoom.ViewChangeStarted += semanticZoom_ViewChangeStarted;
}

void semanticZoom_ViewChangeStarted(object sender, SemanticZoomViewChangedEventArgs e)
{
    if (e.SourceItem == null)
        return;

    if (e.SourceItem.Item.GetType() == typeof(HeaderItem))
    {
        HeaderItem hi = (HeaderItem)e.SourceItem.Item;

        var group = dataLetter.Find(d => ((char)d.Key) == hi.Name);
        if (group != null)
            e.DestinationItem = new SemanticZoomLocation() { Item = group };
    }
}

// FilmData looks like this
private List<GroupInfoList<object>> groupsByLetter = null;

public List<GroupInfoList<object>> GroupsByLetter
{
    get
    {
        if (groupsByLetter == null)
        {
            groupsByLetter = new List<GroupInfoList<object>>();

            var query = from item in Collection
                        orderby ((FilmInfo)item).Title
                        group item by ((FilmInfo)item).HeaderChar into g
                        select new { GroupName = g.Key, Items = g };

            foreach (var g in query)
            {
                GroupInfoList<object> info = new GroupInfoList<object>();
                info.Key = g.GroupName;
                foreach (var item in g.Items)
                {
                    info.Add(item);
                }
                groupsByLetter.Add(info);
            }
        }

        return groupsByLetter;
    }
}

List<HeaderItem> filmHeaders = null;
public List<HeaderItem> FilmHeaders
{
    get
    {
        if (filmHeaders == null)
        {
            filmHeaders = new List<HeaderItem>();

            char c = '#';

            filmHeaders.Add(new HeaderItem() { Name = '#', IsEnabled = this.GroupsByLetter.Exists(k => ((char)k.Key) == c) });
                    
            for (int i = 65; i <= 90; i++)
            {
                c = (char)i;

                if (this.GroupsByLetter.Exists(k => ((char)k.Key) == c))
                    filmHeaders.Add(new HeaderItem() { Name = c, IsEnabled = true });
                else
                    filmHeaders.Add(new HeaderItem() { Name = c, IsEnabled = false });
            }                    
         }

        return filmHeaders;
    }
}

I think that’s about it. Its been 6 months now and I think I am going to change how it looks some stuff will remain as it is, others will have to change

Geolocator and MovementThreshold #wpdev #win8dev

Last few months, I have had too much on my plate. Been doing lot to Windows 8 and Phone development. Surprisingly Microsoft UK is keeping tabs on phone developers who aren’t adapting to #WP8 and seemingly, I was invited to a dev event targeting the likes of me

Sure I am going and in anticipation of the event, I decided to port Cineworld app to WP8. Its been a challenging task. Reworking a few bits of LongListSelector, Visual Studio / Blend disliking all the xaml and of course a button style causing xaml exception. If that wasn’t enough:

Having used Geolocator in Windows 8 app, I decided to use the same for WP8 as its usually a lot faster than GeoCoordinateWatcher. I moved the code to be more like Win8 and noticed that the location detection was flaky at best. Now I did the stupid thing and like in WP7 version, I decided to set both DesiredAccuracy to High and MovementThreshold to 0 thinking absolutely nothing.

Of course that didn’t help it, it made matters worse, instead of flaky behaviour, it decided to call it quits.

var pos = await locator.GetGeopositionAsync(TimeSpan.FromMinutes(5), TimeSpan.FromSeconds(2));

instead of timing out, it started to hang. In desperation, I started looking at other events exposed by this class and tried hooking into StatusChanged event. Now things were bad, I noticed that it was getting operation aborted exception and decided that something was seriously wrong and that I should take a nap instead

Of course the problem was still there when I woke up the next day its only later that I decided to search on Geolocation and operation aborted and realised that I wasn’t the only one and it was all my fault – causality of me setting the MovementThreshold to 0. I set it to 10 instead and bingo.. it all works.

While I didn’t find it, I hope this post helps people like an earlier post helped me.

MVVM and me – Part 3

Today is continuation of yesterday’s post.

Yesterday my goal was to find out how one goes about setting static page strings in MVVM. There are many ways.

1. Hard code it directly in xaml
2. Define resources in App.xaml
3. Use Resource Dictionary

I have used ResourceDictionary a lot in past when dealing with Localization and I think that is the only right way to set xaml strings. That takes care of present and future need without being too bulky

By default my WP8 project added support for Localisation, It created Resource folder with AppResources.resx, LocalizedString class that exposes the resources and finally set it as a resource in App.xaml.

All you then do is set the strings like this

<TextBlock Text="{Binding LocalizedResources.MainViewChoiceText, Source={StaticResource LocalizedStrings}}" Margin="12, 0"/>

All sorted. And in case you decide to localise your apps, all you need to do is add more resx files.

MVVM and me – Part 2

I could have done this post yesterday but that would have been a long essay. Today we are going to look at displaying static data on XAML pages.

In C# when you have data that does not change, one tends to use const or static readonly. const causes compiler to replace all occurrences of variable usage with the actual data at compile time. That means you assemblies has no lookups at run-time. Static read-only is a static variable that can also be set in constructor – is read-only otherwise.

Now based on my previous experience doing WinForms and Webforms, normally I tend to set those directly in XAML. Say you want to content of a button or a textblock text (label). So the ideal way would be.

1. Take View Model
2. Define consts
3. Set bindings to consts
4. Compile and reload

Eureka.. there’s nothing..

Well XAML bindings make a big fuss of INotifyPropertyChanged interface. From sample I know that it works with properties so could it be that ?

Lets start:

1. Take View Model
2. Define consts
3. Define properties
4. Set property in the constructor to consts
5. Set bindings to properties
6. Compile and reload

There.. much better..

Lesson, const and compiler time optimisations are no good.. you need to define properties and additionally call PropertyChanged events and what not including set the properties at VM Creation in order to display data the proper MVVM way. A Single task of setting a text to a textblock or a button is translated into a handful tasks..

Update 1:
My friend @Scottisafool … suggested an alternative approach that he tends to use

1. Define resources in App.xaml
2. Set bindings to resources
3. Compile and reload

This also works.. sure it means that all your strings are in one place but that’s still not MVVM
So it turns out there is not right way but there is a wrong way!! Everything else but code-behind as the last resource is the pukka MVVM way. Wrap up for today I think.

Update 2:
More messages suggesting that the mechanism to declare labels is to either hard code those or use Resources. That’s all fine.. I could use ResourceDictionary just in case the future me might want to localise the app.

That however still leaves the need to support of real consts impossible. There isn’t any support for those in bindings wrt View Model

Background Audio #win8dev #winrt

In this post I am going to detail some of the work I have been doing on Background Audio. But before I get onto it, let me say that the last few months have been crazy / busy, not highly motivational for personal dev etc. I have done a few updates over the last few months but no new development until this month.

About 2 weeks back I started work on Porting Slydr code to WPF control and that was a breeze. Infact last night I saw something about a simple app being tested.. makes me think on whether I should beat them to it or not.

Now back to Background Audio. With Windows Phone, one had to create a Background Audio Player which the app and system would then communicate with. The app could kick the Background Audio Player off and then exit and the audio would keep on playing. I have talked about this before and will saying it again. WPDev 7x provided many ways of playing audio. With Windows 8 and #WinRT your options are restricted. I have gotten used to giving MediaElement more usage and credit for what it does.

<MediaElement x:Name="mePlayer" />

All you need to do is set the Source property and then call Play(). The audio starts playing. If the app gets suspended, the music stops playing. To enable background audio there are a number of things you need to do.
* Firstly set MediaElement‘s AudioCategory to BackgroundCapableMedia. This still doesn’t activate the Background Audio as its only the first step

* Now open package.appmanifest file. Open the Declarations tab and add Background Tasks. While you are there set the Supported task types property to Audio and Control Channel. You will also need to set the Start page in App settings. Of course now that you have done this, you will have to create a Badge logo before you can save the changes to appmanifest.

* Now back to codebehind of your page and add event handlers for MediaControl‘s PlayPressed, PausePressed, StopPressed and PlayPauseTogglePressed events

In my app I also support Previous Track / Next Track so I additionally added support for PreviousTrackPressed and NextTrackPressed events.

MediaControl.PlayPressed += MediaControl_PlayPressed;
MediaControl.PausePressed += MediaControl_StopPressed;
MediaControl.StopPressed += MediaControl_StopPressed;
MediaControl.PlayPauseTogglePressed += MediaControl_PlayPauseTogglePressed;
MediaControl.NextTrackPressed += MediaControl_NextTrackPressed;
MediaControl.PreviousTrackPressed += MediaControl_PreviousTrackPressed;

and

void MediaControl_PreviousTrackPressed(object sender, object e)
{
    this.Previous();
}

void MediaControl_NextTrackPressed(object sender, object e)
{
    this.Next();
}

void MediaControl_PlayPauseTogglePressed(object sender, object e)
{
    if (MediaControl.IsPlaying)
        this.Stop();
    else
        this.Play();
}

void MediaControl_StopPressed(object sender, object e)
{
    this.Stop();
}

void MediaControl_PlayPressed(object sender, object e)
{
    this.Play();
}

Now when you run the app, initiate the audio playback and navigate away from the app.. Bingo. the audio is still playing.

Slides and Sample Code from Async Task talk

I have uploaded sample from from my async task talk I did last week on github.
https://github.com/hermitdave/AsyncTask

Here is the slide from the talk – Async Programming.

I started by talking about Event based async.. how framework converted sync WCF methods into event driven async methods when one adds a reference for Silverlight or Winddows Phone or Windows 8 projects. I further explained that if you had multiple dependent calls and how async task might actually help.

Next up for a very simple explanation of async task. how async task code creates a dynamic structure which is used to execute the actual code. I mentioned how async task is run on the same thread the current execution is suspended. This raised many questions.. I tried to unsatisfactorily explain the mechanism (by the looks of it). The idea was to talk through individual samples. So next I fired up App and VS and talked individual samples.

There was a hairy project moment when I was trying to show multi-threading using async task.

I think it was okay.. maybe I should have chosen an easier subject ? maybe I just need to sound more convincing next time. I am also going to have comparable async event samples side by side. There were some comments. 1st one was the same day.. very critical comment suggesting that I knew nothing (as I said async does not result in creation of new threads for execution of the said code). The chap further critisied my samples are overly simple.. and finally my projector skills (issues during the last part of event).

Oh well.. Should I continue talking on the subject ?

Why would you ever use async void

Suppose you have a method that uses async task mechanism. Simplest example would be say displaying MessageDialog. Example I will use is using Launcher class to launch browser with a Url.

string BingMapsUri = String.Format("http://www.bing.com/maps/default.aspx?cp={0}~{1}&lvl=18&style=u", latitude, longitute);
 Uri uri = new Uri(BingMapsUri, UriKind.Absolute);
 await Launcher.LaunchUriAsync(uri);

this will launch the default browser with the uri above. Suppose you had an appbar button and you wanted to use click or tapped event to execute above code. The click event handler by default looks like this

private void btnViewOnMap_Click(object sender, RoutedEventArgs e)
{
}

one way would be to declare btnViewOnMap_Click to return Task and declare it async.

private async Task btnViewOnMap_Click(object sender, RoutedEventArgs e)
{
}

However event handlers do not like this and will refuse to work. In my early Win8 dev days I was stumped by this… what the heck was I supposed to do ? The answer was simple.

private async void btnViewOnMap_Click(object sender, RoutedEventArgs e)
{
}

just add async declaration to the event handler. this just informs the framework that this method will make and await async tasks. the event handler would look like this

private async void btnViewOnMap_Click(object sender, RoutedEventArgs e)
{
    string BingMapsUri = String.Format("http://www.bing.com/maps/default.aspx?cp={0}~{1}&lvl=18&style=u", latitude, longitute);
    Uri uri = new Uri(BingMapsUri, UriKind.Absolute);
    await Launcher.LaunchUriAsync(uri);
}

That is the only use of async void. In all other circumstances, you should use async Task

Quirk: App invocation from secondary tile with app currently running #win8dev

My cineworld app for Windows 8 is now in Store and thanks to many of my dev friends, I am getting bug reports and feature requests.

Anthony Wieser just found another bug for me. The app is running and you have two cinemas in pinned state: Enfield and Cambridge. Hit Start and open one of the pinned cinema, the app shows the view you left it at. No navigation to desired cinema.

To resolve this issue, I set the app to debug and then opened App.xaml.cs and as I was putting a break point in OnActivatedMethod, I saw this

// Do not repeat app initialization when already running, just ensure that
// the window is active
if (args.PreviousExecutionState == ApplicationExecutionState.Running)
{
   Window.Current.Activate();
   return;
}

var rootFrame = new Frame();
SuspensionManager.RegisterFrame(rootFrame, "AppFrame");

if (rootFrame.Content == null)
{
... // so on and so forth
}

this is the culprit. What I should be doing is checking params passed and then showing the correct xaml page. time to fix it now.

Update: Fixed. here’s what I have done

if (args.PreviousExecutionState == ApplicationExecutionState.Running)
{
    if (iCin == int.MinValue)
    {
        Window.Current.Activate();
        return;
    }
    else
        rootFrame = (Frame)Window.Current.Content;
}
else
{
    // Create a Frame to act as the navigation context and associate it with
    // a SuspensionManager key
    rootFrame = new Frame();
    SuspensionManager.RegisterFrame(rootFrame, "AppFrame");
}

if (rootFrame.Content == null || iCin != int.MinValue) // the iCin contain value passed in activation param
{
... // so on and so forth
}

once you do this, you can handle navigation params and navigate to correct xaml page.

Implement Search Contract the easy way #win8dev

Most apps contain some sort of data that you as a developer would like exposed. That’s were the Search Contract comes into play. Say the user is on the start screen and wishes to search your app, they could just start typing and select your app from the list. If you implemented Search contract, your app will be listed in the app list and the user could just type away and hit enter to see results. That would be nice wouldn’t it ?

Lets get on with it and add search contract in a simple / easy way.
Right click on the Win8 project and select Search Contract. Name it whatever you wish and hit enter.

This does two things:

• Adds override for OnSearchActivated in your App.xaml.cs
• Adds required page for search and display of results.

This is what the OnSearchActivated looks like

protected async override void OnSearchActivated(Windows.ApplicationModel.Activation.SearchActivatedEventArgs args)
{
    // TODO: Register the Windows.ApplicationModel.Search.SearchPane.GetForCurrentView().QuerySubmitted

    // event in OnWindowCreated to speed up searches once the application is already running

    // If the Window isn't already using Frame navigation, insert our own Frame
    var previousContent = Window.Current.Content;
    var frame = previousContent as Frame;

    // If the app does not contain a top-level frame, it is possible that this 
    // is the initial launch of the app. Typically this method and OnLaunched 
    // in App.xaml.cs can call a common method.
    if (frame == null)
    {
        // Create a Frame to act as the navigation context and associate it with
        // a SuspensionManager key
        frame = new Frame();
        Cineworld.Common.SuspensionManager.RegisterFrame(frame, "AppFrame");

        if (args.PreviousExecutionState == ApplicationExecutionState.Terminated)
        {
            // Restore the saved session state only when appropriate
            try
            {
                await Cineworld.Common.SuspensionManager.RestoreAsync();
            }
            catch //(Cineworld.Common.SuspensionManagerException)
            {
                //Something went wrong restoring state.
                //Assume there is no state and continue
            }
        }
    }

    frame.Navigate(typeof(SearchResults), args.QueryText);
    Window.Current.Content = frame;

    // Ensure the current window is active
    Window.Current.Activate();
}

as you can see it is passing the search query to the Search Results page while navigating.
Now lets look at the code-behind in SearchResults.xaml.
FYI, I am loading my dataset if required in the OnNavigatedTo method. This page is a simple results display page. It contains GridView / ListView to display results. Lets look at the LoadState method

protected override void LoadState(Object navigationParameter, Dictionary<String, Object> pageState)
{
    var queryText = navigationParameter as String;

    List<SearchResult> matches = new List<SearchResult>();

    foreach (var f in App.Films.Values)
    {
        IEnumerable<CastInfo> casts = from cast in f.FilmCast
                                        where cast.Name.StartsWith(queryText, StringComparison.CurrentCultureIgnoreCase)
                                        select cast;

        foreach (var c in casts)
        {
            //searchCinemas.Add(c.Name, c);
            matches.Add(new SearchResult() { Name = c.Name, Subtitle = String.Format("{0} in {1}", c.Character, f.Title), SearchObject = f, Image = c.ProfilePath });
        }
    }

    IEnumerable<FilmInfo> films = from film in App.Films.Values
                                    where film.Title.StartsWith(queryText, StringComparison.CurrentCultureIgnoreCase)
                                    select film;

    searchFilms.Clear();
    searchCinemas.Clear();

    foreach (var f in films)
    {
        searchFilms.Add(f.Title, f);
        matches.Add(new SearchResult() { Name = f.Title, Image = f.PosterUrl, SearchObject = f });
    }

    IEnumerable<CinemaInfo> cinemas = from cinema in App.Cinemas.Values
                                        where cinema.Name.StartsWith(queryText, StringComparison.CurrentCultureIgnoreCase)
                                        select cinema;

    foreach (var c in cinemas)
    {
        searchCinemas.Add(c.Name, c);
        matches.Add(new SearchResult() { Name = c.Name, SearchObject = c, Image = new Uri("ms-appx:///Assets/Background.png") });
    }
            
    // TODO: Application-specific searching logic.  The search process is responsible for
    //       creating a list of user-selectable result categories:
    //
    //       filterList.Add(new Filter("<filter name>", <result count>));
    //
    //       Only the first filter, typically "All", should pass true as a third argument in
    //       order to start in an active state.  Results for the active filter are provided
    //       in Filter_SelectionChanged below.

    // Communicate results through the view model
    this.DefaultViewModel["QueryText"] = '\u201c' + queryText + '\u201d';

    bAllowNav = false;

    this.DefaultViewModel["Results"] = matches;

    bAllowNav = true;

    var filterList = new List<Filter>();
    filterList.Add(new Filter("All", 0, true));

    //this.DefaultViewModel["Filters"] = filterList;
    //this.DefaultViewModel["ShowFilters"] = filterList.Count > 1;
}

I added code to search my dataset and to add results to DefaultViewModel. I don’t use MVVM but the default code implemented basic binding etc and I thought I’d leave it at that. I accumulate the results and save them and let bindings do the rest. Let me show you how it looks
Say I got to start screen, type I ben and select my app, this is what I get.

Now you have a nice list of matched entries. Now suppose I wanted to let users click on a matched entry and to navigate them to details page ? I implemented GridView ItemClick event (SelectionChanged doesn’t work for some reason)

private void resultsGridView_ItemClick(object sender, ItemClickEventArgs e)
{
    if (e.ClickedItem != null && bAllowNav)
    {
        SearchResult res = (SearchResult)e.ClickedItem;
        if (res.SearchObject is FilmInfo)
        {
            FilmDetails.SelectedFilm = (res.SearchObject as FilmInfo);
            this.Frame.Navigate(typeof(FilmDetails));
        }
        else if (res.SearchObject is CinemaInfo)
        {
            CinemaDetails.SelectedCinema = (res.SearchObject as CinemaInfo);
            this.Frame.Navigate(typeof(CinemaDetails));
        }
    }
}

Hope this post is helpful to others looking to implement the search contract. Happy coding!

#async task and the for loop bug

I have used various flavours of async task implementation.
* WP7 / async CTP / v3 VS 2010
* Win8 / VS 2012
* Azure / VS 2012
* SL / async targetting pack / VS 2012

I blogged about how i had issues with #async on #aszure and funnily enough i wasn’t the only one. As discussed in http://invokeit.wordpress.com/2012/11/07/windows-azure-and-async-task-mechanism-async/ if you use something like this

AsyncDataSourceObj aeo = new AsyncDataSourceObj();

protected async Task BuildFilmDataSet()
{
    Films films = await aeo.GetFilmData();
    foreach(var film in films)
    {
        Cinemas cinemas = await aeo.GetCinemaData(film);

        // do things

        // do more things 
    }
}

It doesn’t work and a little investigation showed me that i wasn’t doing anything wrong.

The moment await aeo.GetCinemaData(film); gets called, the execution instead of awaiting moves to the next iteration of for loop. Why in the world you would want that ? I am sure if you wanted that one would have used Parallel.For instead.

For some reason, the creators thought that we clever people wouldn’t ever want to do a async call in for loop. I mean its not like its the most common loop usage etc…

The suggestion is to use Task.Yield() (or TaskEx.Yield) within for loop

It however doesn’t always work. I have tried it with my last Silverlight + Async Targetting pack and its still the same. Infact I had to revert to event based async in that case.

Here’s a screen of azure sample in action