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Leaderboard for Windows Phone 7 XNA Game

, 27 Feb 2012
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Solution for creating a Leaderboard for a Windows Phone 7 (WP7) XNA game

336116/highscore.gif

Old School High Score Table borrowed from Coding Horror

Introduction

This article discusses a solution for creating an active Leaderboard for a Windows Phone 7 (WP7) XNA game so that game scores can be posted to a back-end repository and a Leaderboard of the top ten scores can be displayed within the game.

Background

I am working on developing a series of casual puzzle games for WP7. One of the features that I want to implement in these games is an active Leaderboard or High Score Table. When a player completes a game, the game will post the score to a web page. The mobile device can also request the Leaderboard from the web page.

As I want my Leaderboard functionality to work with my existing website, I want to implement a simple web page that will accept requests for the current Leaderboard and accept new game scores from WP7 devices.

Using the code

Database

As my Internet host provider uses SQL Server as a back-end database, I will use the same for this article so that I can plug this solution into my current web site.

To get started with the database, I created a new database in Microsoft SQL Server Management Studio called "Leaderboard". Within this "Leaderboard" database, I created a new table also called "Leaderboard" with the following scheme:

     CREATE TABLE [dbo].[Leaderboard](
    [RowId] [int] IDENTITY(1,1) NOT NULL,
    [GameId] [int] NOT NULL,
    [PlayerId] [int] NOT NULL,
    [Score] [int] NOT NULL,
    [Moves] [int] NOT NULL,
    [TimestampUTC] [datetime] NOT NULL,
    [TimestampServer] [datetime] NOT NULL,
    [TimestampDevice] [datetime] NULL,
    [IPAddress] [nvarchar](50) NULL,
    [CountryCode] [nvarchar](50) NULL,
    [CountryName] [nvarchar](50) NULL,
    [RegionName] [nvarchar](50) NULL,
    [CityName] [nvarchar](50) NULL,
    [ZipPostalCode] [nvarchar](50) NULL,
    [Latitude] [nvarchar](50) NULL,
    [Longitude] [nvarchar](50) NULL,
    [GmtOffset] [nvarchar](50) NULL
) ON [PRIMARY]

RowId is an INT Identity field. TimestampUTC defaults to GETUTCDATE() and TimestampServer defaults to GETDATE().

You should have an additional table with player information that you can create a relationship to on the PlayerId, but to keep this article simple, I am just displaying the PlayerId in the Leaderboard.

ASP.NET

The service can be written in a few different ways.

One way is to create a web page that will accept a query string which it parses to get the relevant data and then writes that data to the database. The same page can also return the existing Leaderboard with the correct parameters in the query string.

Another way is to create a web service to handle the Leaderboard requests.

Posting High Scores

GEO Location Information

In the ASP.NET code, I am using the IP address reported by the WP7 device to get additional GEO Location information. I was thinking I could use this information in a future GEO Location game feature. If you want to use this feature, you will need to get a free API key from IPInfoDB. Otherwise, if you’re not interested in this functionality, just comment out this whole try/catch block of code.

try
{
    // Get your own API key at http://ipinfodb.com
    string ApiKey = "xxxx you'll need to get your own api key xxxx";
    string ApiUrlFormat = "http://api.ipinfodb.com/v3/ip-city/?key={0}&ip={1}";

    string reqUrl = string.Format(ApiUrlFormat, ApiKey, IpAddress);
    HttpWebRequest httpReq = (HttpWebRequest) HttpWebRequest.Create(reqUrl);
    string webResponseString = string.Empty;
    HttpWebResponse webResponse = (HttpWebResponse) httpReq.GetResponse();

    using (StreamReader reader = new StreamReader(webResponse.GetResponseStream()))
    {
        webResponseString = reader.ReadToEnd();
    }

    string[] webResponseArray = webResponseString.Split(';');

    if (webResponseArray.Length > 0)
    {
        apiStatus = webResponseArray[0];
        apiIp = webResponseArray[2];
        apiCountryCode = webResponseArray[3];
        apiCountyName = webResponseArray[4];
        apiRegionName = webResponseArray[5];
        apiCityName = webResponseArray[6];
        apiZipPostalCode = webResponseArray[7];
        apiLatitude = webResponseArray[8];
        apiLongitude = webResponseArray[9];
        apiGmtOffset = webResponseArray[10];
    }
}

Requesting Leaderboard

When the Leaderboard is requested by a WP7 device, the web page queries the database for the relevant information. Once the requested data is in a DataTable, the DataTable's WriteXml() method is called to write the data and data structure out to a string with XML formatting. This block of XML is sent to the requesting WP7 device.

dataTable = dataSet.Tables[0];
using (StringWriter stringWriter = new StringWriter())
{
    dataTable.WriteXml(stringWriter);
    result = stringWriter.ToString().Trim();
}
    

For testing purposes, I had to set the Response object Cache to expire after one second, otherwise I could not see quick updates on the WP7 device. This setting should be moved to the web.config so that it can be changed later if needed.

Response.Cache.SetExpires(DateTime.Now.AddSeconds(1));
        

Windows Phone 7

The WP7 project is a bare minimum XNA project.

User Interface

The WP7 User Interface simply includes two buttons. The "Post Score" button posts a random game score to the web page. The "Get Scores" button requests the Leaderboard from the web page and displays it on the WP7 screen.

Posting A Score

To get the IP address of the WP7 device, an asynchronous call is made to http://whatismyip.org.

Uri uri = new Uri("http://whatismyip.org");
WebClient webClient = new WebClient();
webClient.DownloadStringCompleted += new DownloadStringCompletedEventHandler(Address_DownloadStringCompleted);
webClient.DownloadStringAsync(uri); 
           

Once the IP address of the WP7 device is known, the score is posted to the web page

string IpAddress = e.Result;

string GameId = "1";
string PlayerId = "21";
string Score = new Random().Next(999).ToString();
string Moves = new Random().Next(100).ToString();

string PostFormat = "post={0}|{1}|{2}|{3}|{4}";
string Post = String.Format(PostFormat, GameId, PlayerId, Score, Moves, IpAddress);

Uri uri = new Uri("http://localhost:45291/Leaderboard.aspx?" + Post);
WebClient webClient = new WebClient();
webClient.DownloadStringCompleted += new DownloadStringCompletedEventHandler(PostScore_DownloadStringCompleted);
webClient.DownloadStringAsync(uri);
        

Here, the GameId is the ID of the current game being played. The GameId is passed so that the Leaderboard can maintain High Scores for different games. Sounds good in theory, but might not work well in practice if different games keep scores in different ways.

The PlayerId is the player ID of the current player. Some kind of registration system should be implemented so that players can register. But, for now, that is beyond the scope of this article.

The current URL is set for testing.

Requesting the Leaderboard

The Leaderboard is requested by passing the GameId to the web page in an asynchronous call. The current URL is set for testing.

Uri uri = new Uri("http://localhost:45291/Leaderboard.aspx?request=1");
WebClient webClient = new WebClient();
webClient.DownloadStringCompleted += new DownloadStringCompletedEventHandler(Leaderboard_DownloadStringCompleted);
webClient.DownloadStringAsync(uri);             
        
Regular Expression

Regular Expression is used to make sure we only get the XML block between the <Leaderboard> tags, inclusive. The rest of the response object is ignored.

result = result.Replace(System.Environment.NewLine, string.Empty);
result = result.Trim();
string xml_block = string.Empty;
System.Text.RegularExpressions.MatchCollection matchCollectionTitle = System.Text.RegularExpressions.Regex.Matches(result, @"
<leaderboard>(.*?)</Leaderboard>");
if (matchCollectionTitle.Count == 1)
{
    xml_block = matchCollectionTitle[0].Value;
}
        
Converting the XML block to an XML Document

Now that we have our cleaned up XML block, it is converted to an XML document for processing. The xml block string is converted to a byte array. From there it is converted to a memory stream. The memory stream is then converted to a stream reader. Finally we have the xml block in a format that can be loaded into an XML document.

byte[] byteArray = Encoding.UTF8.GetBytes(xml_block);
MemoryStream stream = new MemoryStream(byteArray);

StreamReader streamReader = new StreamReader(stream);

XDocument doc = XDocument.Load(streamReader);     
        
LINQ and Anonymous Objects

Once the XML document is created, the magic of LINQ and Anonymous objects is used to parse the XML document and populate the Leaderboard.

var xmlLeaderboardEntries = from xmlLeaderboardEntry in doc.Descendants("Table")
                select new
                    {
                        PlayerId = xmlLeaderboardEntry.Element("PlayerId").Value,
                        Score = xmlLeaderboardEntry.Element("Score").Value,
                        Moves = xmlLeaderboardEntry.Element("Moves").Value,
                        TimestampUTC = xmlLeaderboardEntry.Element("TimestampUTC").Value,
                    };

leaderboard.Clear();
foreach (var xmlLeaderboardEntry in xmlLeaderboardEntries)
{
    LeaderboardEntry leaderboardEntry = new LeaderboardEntry();
    leaderboardEntry.PlayerId = xmlLeaderboardEntry.PlayerId;
    leaderboardEntry.Score = xmlLeaderboardEntry.Score;
    leaderboardEntry.Moves = xmlLeaderboardEntry.Moves;
    leaderboardEntry.TimestampUTC = xmlLeaderboardEntry.TimestampUTC;
    leaderboard.Add(leaderboardEntry);
}      
        

Testing

To test the solution, load and execute the web project in one instance of Visual Studio 2010 (VS2010). Load the WP7 project in a second instance of VS2010. Run the WP7 project in the WP7 emulator.

On the WP7 emulator, click "Post Score" to post some random score data.

Click "Get Scores" to retrieve the current Leaderboard.

336116/wp7_1.png 336116/wp7_2.png

Points of Interest

One issue that I ran into was that when I was repeatedly attempting to update the Leaderboard from within the WP7 project, the Leaderboard did not change. The WP7 project kept getting a cached copy of the response. After some research I found a few solutions for this issue.

I added a line to the ASP.NET code to cause the response object cache to expire after one second.

Alternatively, you can add an additional field to the query string in the WP7 project to include a random number or perhaps a datetime stamp. This will cause the server to always send fresh data rather than a cached copy.

Still To Do

The functionality for the solution described in this article is really a proof of concept. I need to deploy solution to my website, implement the Leaderboard code with in one of my Windows Phone 7 games and give it a test drive. I plan on implementing some additional features before moving the solution to my web host:

  • Move connection string and other hardcoded configuration settings to web.config file<
  • Move SQL code from C# to stored procedures in the database itself
  • Encrypt the data sent to and from the mobile device
  • Implement some kind of authentication between mobile device and ASP.NET

Summary

Let me know what you think of this article and the solution. Any questions, concerns and critics are welcome.

References

Links

  • http://ipinfodb.com

History

2012-02-26 Initial Article

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

BillLange1968
Software Developer Citrix
United States United States
Bill is a senior software engineer. He designs and developments cloud based, web accessible on-demand provisioning system used for provisioning Citrix-based training and demo environments in Visual Studio 2010, .NET Framework, C# and SQL Server 2008. He resides in NJ with his wife Lucy and their dog Yoda.
 
Prior to web development, he spent seven years in the mobile enterprise space working at companies such as Peak Technologies, Countermind, and Blue Dot Solutions in the Denver, Colorado metropolitan area building enterprise solutions in the .Net Compact Framework, XML and SQL. He also has significant experience in the telecommunication space with various roles at AT&T Bell Laboratories, Lucent Technologies and Avaya where he worked on development and localization of the AUDIX platform and other voice messaging technologies.
 
Having spend his salad days playing around with his Atari 400, in his spare time, he likes to tinker with game programming, 8-bit computers and the classic arcade machines of his youth.
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GeneralMy vote of 5 PinmvpKanasz Robert21-Sep-12 1:34 
GeneralMy vote of 5 PinmemberCaio.Lib27-Jul-12 8:29 
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