Windows Phone, a great dev platform: adding leaderboards to 4th & Mayor in 30 minutes

Posted 20 March 2011  

It’s just amazing how efficient the Windows Phone (powered by Silverlight) dev environment can be. I’m a little biased here (yeah yeah I work on the team), but wanted to start of my app development series with a short example of just how quickly the platform can enable rapid changes and innovation.

At SXSW a little over a week ago, foursquare introduced the new ‘fsq3’ version of their apps for iPhone, Android, and I believe eventually Blackberry, too, though not initially. Foursquare has always been about a fun time, exploring the city as part of a massive, worldwide-game, and so they did some nice work in version 3 to bring in a little more fun: every time you check-in to a place, there’s a leaderboard (relative to all of your friends) that appears, showing your latest scores and your close competition.

It took about 30 minutes to add this feature to my foursquare app, sadly this blog post will probably take 60 minutes to prepare.

The steps really are:

  • Parsing the JSON of the added data
  • Creating a new data/model item
  • Designing and creating new XAML templates for presenting the data
  • Updating the data template selector for the added notification type
  • Binding the data and making the magic happen

Here’s what it looks like on an iPhone – the new “Leaderboard” section is of interest. Interestingly, the Android app for foursquare is pretty much a clone of the iPhone app… so no need to really highlight that.

The way that this is implemented on the foursquare service side is a simple new “notification” type that comes in after a check-in or other action. When working with services like this, as a developer it’s more important than ever to be resilient against “invalid” or unknown data and types – lots of null checks, default handling clauses, etc. So foursquare added a new leaderboard notification type to the others (such as mayor status, a recommended tip at a place, etc.)

The code I wrote to handle notifications started with a simple set of parsing methods. Notifications can actually come from any foursquare web request, but typically it’s just when you check-in. I use (and absolute love!) JSON.NET by James Newton-King - the LINQ to JSON stuff is nice, and it’s a lot better than the JSON stuff built into the platform.

// Notifications is a List<Notification>

public static Notifications ParseJson(JToken json, string venueId)

{

    var ns = new Notifications();



    foreach (var notif in json)

    {

        Notification notification = Notification.ParseJson(notif, venueId);

        if (notification != null)

        {

            ns.Add(notification);

        }

    }



    return ns;

}





public static Notification ParseJson(JToken notification, string venueId)

{

    Notification n = null;



    string type = Checkin.TryGetJsonProperty(notification, "type");

    var item = notification["item"];

    if (item != null)

    {

        switch (type)

        {

            case "message":

                n = new MessageNotification(item);

                break;



            case "badge":

                n = new BadgeNotification(item);

                break;



            case "mayorship":

                n = new MayorshipNotification(item);

                break;



            case "tip":

                n = new RecommendedTipNotification(item);

                break;



            case "leaderboard":

                n = new LeaderboardNotification(item);

                break;



            case "special":

                n = new SpecialNotification(item, venueId);

                break;



            case "score":

                n = new ScoreNotification(item);

                break;



            default:

                var hasMessage = item["message"];

                if (hasMessage != null)

                {

                    n = new MessageNotification(item);

                }



                break;

        }

    }



    return n;

}



namespace JeffWilcox.FourthAndMayor.Model

{

    public class LeaderboardNotification : Notification

    {

        public string Message { get; private set; }



        public List<LeaderboardItem> Leaderboard { get; private set; }



        public LeaderboardNotification(JToken item)

        {

            Message = Checkin.SanitizeString(Checkin.TryGetJsonProperty(item, "message"));



            var leaders = new List<LeaderboardItem>();

            var lj = item["leaderboard"];

            if (lj != null)

            {

                foreach (var victor in lj)

                {

                    var wolverine = LeaderboardItem.ParseJson(victor);

                    if (wolverine != null)

                    {

                        leaders.Add(wolverine);

                    }

                }

            }



            Leaderboard = leaders;

        }

    }

}

And then a switch to handle known notification types and create data model objects from that. This yields a nice strongly typed data object – I personally prefer this to just storing the JSON tree live, or using a property bag, but everyone has their own opinions. Strong typing makes data binding in Silverlight super easy.

The JSON from foursquare looks a lot like this:

{

"type": "mayorship",

"item": {

  "type": "nochange",

  "checkins": 27,

  "message": "You're still the Mayor of Boka Kitchen & Bar! (27 check-ins in the past two months)",

  "image": "http://foursquare.com/img/crown.png"

}

},

{

"type": "leaderboard",

"item": {

  "leaderboard": [

	{

	  "user": {

		"id": "4052351",

		"firstName": "Gilles",

		"lastName": "K",

		"photo": "https://playfoursquare.s3.amazonaws.com/userpix_thumbs/FXM5YX5ABXZARAR1.png",

		"gender": "male",

		"homeCity": "WA",

		"relationship": "friend"

	  },

	  "scores": {

		"recent": 120,

		"max": 127,

		"checkinsCount": 31

	  },

	  "rank": 1

	},

	{

	  "user": {

		"id": "20057",

		"firstName": "Jeff",

		"lastName": "W",

		"photo": "https://playfoursquare.s3.amazonaws.com/userpix_thumbs/RRJIFN1NATUHRN4J.jpg",

		"gender": "male",

		"homeCity": "Seattle, WA",

		"relationship": "self"

	  },

	  "scores": {

		"recent": 117,

		"max": 124,

		"checkinsCount": 49

	  },

	  "rank": 2

	},

	{

	  "user": {

		"id": "130986",

		"firstName": "Tim",

		"lastName": "H",

		"photo": "https://playfoursquare.s3.amazonaws.com/userpix_thumbs/4A52T22PCNGR11EM.jpg",

		"gender": "male",

		"homeCity": "WA",

		"relationship": "friend"

	  },

	  "scores": {

		"recent": 116,

		"max": 125,

		"checkinsCount": 41

	  },

	  "rank": 3

	}

  ],

  "message": "You jumped ahead of Tim!",

  "scores": [

	{

	  "points": 3,

	  "icon": "https://playfoursquare.s3.amazonaws.com/static/img/points/mayor.png",

	  "message": "You're the Mayor!"

	}

  ],

  "total": 3

}

},

And so at runtime, when you check-in, you’ll end up with this return result being stored. Since I’ve already coded in my app simple parsing methods for CompactUsers, it’s easy to work with this rich hierarchical data.

In my checkin (“what’s new”) window of 4th & Mayor I’ve a very simple items control that is used to expand at runtime the data objects into a nice visual presentation. Now in Silverlight 3 (the version that was forked for Windows Phone initially) there isn’t a way to have implicit “data templates” that key off of type, so I did have to do a little hacking. But this is super easy.

Here’s my data template selector that I wrote as a value converter. I expose public properties of type DataTemplate:

namespace JeffWilcox.FourthAndMayor.Converters

{

    public class NotificationDataTemplateSelector : IValueConverter

    {

        public DataTemplate MessageTemplate { get; set; }

        public DataTemplate MayorTemplate { get; set; }

        public DataTemplate BadgeTemplate { get; set; }

        public DataTemplate TipTemplate { get; set; }

        public DataTemplate ScoreTemplate { get; set; }

        public DataTemplate SpecialTemplate { get; set; }

        public DataTemplate LeaderboardTemplate { get; set; }



        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)

        {

            ScoreNotification sn = value as ScoreNotification;

            if (sn != null)

            {

                return ScoreTemplate;

            }



            BadgeNotification bn = value as BadgeNotification;

            if (bn != null)

            {

                return BadgeTemplate;

            }



            MayorshipNotification mn = value as MayorshipNotification;

            if (mn != null)

            {

                return MayorTemplate;

            }



            LeaderboardNotification ln = value as LeaderboardNotification;

            if (ln != null)

            {

                return LeaderboardTemplate;

            }



            RecommendedTipNotification tip = value as RecommendedTipNotification;

            if (tip != null)

            {

                return TipTemplate;

            }



            MessageNotification msg = value as MessageNotification;

            if (msg != null)

            {

                return MessageTemplate;

            }



            var special = value as SpecialNotification;

            if (special != null)

            {

                return SpecialTemplate;

            }



            return null;

        }



        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)

        {

            throw new NotImplementedException();

        }

    }

}

And then on my check-in page, in the page’s resources, I define the individual data templates that I would like different notification data objects to appear as. XAML is pretty verbose but wow, powerful. I hand-edited many of my data templates. And I’m picky, I prefer one attribute per line in most situations – it makes diffs in source control a lot easier to understand and work with, especially while integrating.

<DataTemplate x:Key="Leaderboard">

    <StackPanel>

		<ContentPresenter Content="Leaderboard"

		                  ContentTemplate="{StaticResource GroupHeader}"/>

        <TextBlock

            Text="{Binding Message}"

            TextWrapping="Wrap"

            Margin="0,0,0,12"

            Style="{StaticResource PhoneTextNormalStyle}"/>

        <ItemsControl ItemsSource="{Binding Leaderboard}">

            <ItemsControl.ItemTemplate>

                <DataTemplate>

                    <HyperlinkButton Style="{StaticResource NoHyperlink}"

                                HorizontalAlignment="Stretch"

                                HorizontalContentAlignment="Stretch"

                                NavigateUri="{Binding User.UserUri}">

                        <Grid Margin="0,0,0,12">

                            <Grid.ColumnDefinitions>

                                <ColumnDefinition Width="72"/>

                                <ColumnDefinition />

                                <ColumnDefinition Width="88"/>

                            </Grid.ColumnDefinitions>

                            <Grid Grid.Column="0">

                                <Grid 

                                    Width="72" 

                                    Height="72" 

                                    Background="{StaticResource PhoneChromeBrush}">

                                    <Image

                                        jw:AwesomeImage.UriSource="{Binding User.Photo}"

                                        Tag="clear"/>

                                </Grid>

                                <Grid

                                    Background="{StaticResource PhoneAccentBrush}"

                                    Width="12"

                                    HorizontalAlignment="Left"

                                    VerticalAlignment="Stretch"

                                    Visibility="{Binding IsSelf, Converter={StaticResource Vis}}">

                                    <Grid.RenderTransform>

                                        <TranslateTransform X="-24"/>

                                    </Grid.RenderTransform>

                                </Grid>

                            </Grid>

                            <StackPanel 

                                Grid.Column="1"

                                Orientation="Horizontal">

                                <TextBlock

                                    Style="{StaticResource PhoneTextLargeStyle}"

                                    FontFamily="{StaticResource PhoneFontFamilySemiBold}"

                                    VerticalAlignment="Center"

                                    Text="{Binding Rank}"/>

                                <TextBlock

                                    VerticalAlignment="Center"

                                    Margin="0"

                                    Text="{Binding User}"

                                    Style="{StaticResource PhoneTextLargeStyle}"/>

                            </StackPanel>

                            <TextBlock

                                Text="{Binding Scores.Recent}"

                                HorizontalAlignment="Left"

                                VerticalAlignment="Center"

                                Grid.Column="2"

                                Style="{StaticResource PhoneTextLargeStyle}"

                                FontFamily="{StaticResource PhoneFontFamilySemiLight}"/>

                        </Grid>

                    </HyperlinkButton>

                </DataTemplate>

            </ItemsControl.ItemTemplate>

        </ItemsControl>

    </StackPanel>

</DataTemplate>

So next I add an instance of the converter and give it a name. This is designed to associate the XAML data templates with the way to show specific notification object types when the items control expands after binding.

<Converters:NotificationDataTemplateSelector 

    MessageTemplate="{StaticResource Message}"

    BadgeTemplate="{StaticResource Badge}"

    MayorTemplate="{StaticResource Mayor}"

    TipTemplate="{StaticResource PopularTip}"

    ScoreTemplate="{StaticResource Score}"

    LeaderboardTemplate="{StaticResource Leaderboard}"

    SpecialTemplate="{StaticResource Special}"

    x:Key="DataTemplateSelector"/>

And now here’s the items control. Here I bind the ItemsSource to my list of notifications, then use this syntax to use the data template selector:

<jw:AwesomeScrollViewer>

    <StackPanel Margin="12,0,12,12">

        <TextBlock 

            Text="what's new" 

            Margin="9,-7,0,16" 

            Style="{StaticResource PhoneTextTitle1Style}"/>

        <ItemsControl ItemsSource="{Binding}"

                        Margin="0,0,0,24">

            <ItemsControl.ItemTemplate>

                <DataTemplate>

                    <Grid Margin="12,0">

                        <ContentControl

                        HorizontalContentAlignment="Stretch"

                        Content="{Binding}"

                        ContentTemplate="{Binding Converter={StaticResource DataTemplateSelector}}"/>

                    </Grid>

                </DataTemplate>

            </ItemsControl.ItemTemplate>

        </ItemsControl>

    </StackPanel>

</jw:AwesomeScrollViewer>

And at runtime we end up with this great output, now including the new v3 leaderboard feature in under 30 minutes! Building on all the other components in my app, and the rich Silverlight visual tree, I’m able to add features like this really quickly, without worry.

Another nice thing about XAML and data templates: typically there is very little required testing, especially if you’re in the habit of going through code reviews or at least reviewing source control diffs first – if you don’t change the shape of your data, you’re in a pretty good place.

There are a lot of amazing efficiencies possible thanks to XAML. For instance, I have just a few instances in my app of data templates for check-ins, places, tips, etc. Then, whenever I add a new page, I can refer to the existing tip template, so there’s a central places for any visual tweaks or fixes that I make.

Leaderboards to the next level

So there’s also a leaderboard endpoint on the foursquare v2 web service that lets you grab the complete leaderboard of your friends. I was able to add this to the app in another 15 minutes – but that’s for another blog post. At a high level for that,

  • I defined a new model item base that exposes a small list hierarchy – leaderboard items, leaderboard scores, and a leaderboard collection. (5 minutes)
  • Added a data loader class for the ‘leaderboard’ endpoint, powered by AgFx (5 minutes)
  • Added a new pivot item to the current users’ profile page, re-used the exact same “leaderboard” data template from the notifications window done above (5 minutes)

Hope this helps. Oh, and if you’re noticing, these objects are not implementing INotifyPropertyChanged… in my app this sort of data doesn’t change at runtime. You only get a check-in report once for a check-in, with static data. Easy that way.

Jeff Wilcox is a Principal SDE Architect at Microsoft on the Azure team.

Jeff lives in Seattle and is an alumnus of the University of Michigan with a degree in Computer Science.

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