3 Silverlight Architecture Tips with Brad Himelstein

Recently, I dove back into XAML-based development to create some Silverlight plugins for a large web application. Most of my experience in XAML came from writing a WPF application from 2008 to 2009, so I had much to learn about the asynchronous data retrieval paradigm used in Silverlight. I had questions about UI Design Patterns, Service-Oriented Architecture (SOA), and how to reuse class libraries, so I asked Brad Himelstein, from CinCom, if I could pick his brain while we hit a few golf balls. Brad has continued working with Silverlight and WPF for a few years, since we worked together on the aforementioned WPF application.

Below is a summary of his tips as well as some quotes from our conversation.

 

Tip #1: Use Model View ViewModel (MVVM)

Me: “Do you ever use any sort of patterns for the UI?”

Brad: “MVVM

Me: “I am just now getting introduced to that. What are the benefits?”

Brad: “It is great, because you just setup the data context and do all your databinding, and it just magically works. Two-way binding works as well.”

 

Brad identified additional benefits during other parts of the conversation. MVVM’s primary purpose is to separate the concern of the behavior of an application from that of the user-interface design. It is a practical implementation that is cleaner to understand and easier to pass back and forth between designers and developers versus the default approach of placing logic in code-behind files. He provides sample MVVM source code here.

 

Tip #2 Extend Proxy Classes with Shared Custom Code

In my application, I use WCF RIA Services to query server objects and return them to the Silverlight client. This technique simplifies the process of retrieving service data and populating local objects because a local proxy object is created and populated automatically. In Brad’s words, “If the web service returns an object of class ‘Foo’, we don’t need to redefine ‘Foo’ in the Silverlight app.”

Unfortunately, I had a great deal of logic included with the retrieved classes that I also wanted to be able to use in the client. I asked Brad how to elegantly work around this limitation of Service-Oriented Architecture.

Me: “What I was hoping to get with RIA Services was, say I’ve got some class I’m returning from the service. I can load it with data easily but I have additional calculation properties on this class, such as FullName, which is just a property that returns FirstName and LastName concatenated. A local proxy object is created automatically for use in Silverlight, with data populated for FirstName and LastName, but the proxy does not retain calculation logic. Since I have a server-side object that has calculation properties defined, how can I share that code for use with the Silverlight client and the proxy object?”

Brad: “If you know you’re going to use FullName, then just create another string called FullName and set the property on the server so it is passed down to the client in the object, because it is not going to take those calculated properties and bring them down.”

Me: “But then that FullName would have a state when it returns.”

Brad: “Remember, you can extend everything. So on the client side, you can alternatively have your own Foo class, which can be used to extend the partial Foo class that is returned from the server.”

Brad’s suggestion was enough to help me come to a solution that fit my needs.

 

Partial Class Extensions

Let’s use the sample Class “User” to continue our example from above. In such a class, I can place fields of the User, such as FirstName and LastName in one file named User.cs. User class should be defined as a partial class, so we can combine definitions of the class from 2 separate files. Hence, in another file, named UserCalcs.cs, we should define calculated properties, such as FullName. At this point, the server behavior will work as it always would have if we had just implemented all properties and fields in the one file. However, the Silverlight client would not yet know about the FullName property.

 

Shared Files

An important limitation of Silverlight is that it can only reference projects that are compiled as Silverlight projects. In other words, Silverlight cannot natively reuse definitions from standard .NET class libraries. What it can do is recompile normal .cs files into a Silverlight assembly.

To do this, right-click on the Silverlight project in your Visual Studio solution and click Add Existing Item. Navigate to the file that contains the calculated properties, UserCalcs.cs. Click the file, and then click the down arrow next to the Add button. Choose Add As Link.

The Silverlight project will now compile this partial class definition. It will extend the proxy class as well as the server side class from the same file. Therefore, maintenance of those calculated properties can be shared between the client and the server side code from one file.

 

Tip #3 Learn HTML 5

Ok, Brad didn’t actually say this so bluntly, but it was a recurring theme of our discussion. Based on recent information about upcoming Windows (8) releases, Silverlight’s future is unclear. From what I have heard, Microsoft is committed to version 5 of Silverlight (current release is 4) but has made no guarantees beyond that. Windows 8 will have 2 versions of its Internet Explorer 10 browser: tablet and desktop. The tablet version will not allow plugins, like Flash and Silverlight. Some have summarized the decision by stating that from Microsoft’s standpoint, Silverlight is “no longer strategic.”

Still, the death of Silverlight development, especially in corporate environments, is distant. Here is a great Microsoft client decision workflow about the correct technology to leverage based on your needs. I believe it reinforces the idea that even after Windows 8 is released, new Silverlight applications will have their place.

Lastly, even though Windows 8 tablets will not allow Silverlight plugins to be loaded within its browsers, native Windows 8 tablet apps will be developed using WinRT. As Brad informs us, this gives us Silverlight developers hope, as WinRT is still “just C# and XAML.”

 

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How to Query the Yahoo Fantasy Football API in .NET

The Coveted League TrophyAs technical co-commissioner of my Keeper Fantasy Football league, I perform a good deal of administrative duties during the offseason. I have to sort through all the player transactions from the season to determine which NFL players are eligible to be kept within our league rules. One year, at the end of the 2010 season, I waited too long to gather this data. I normally click through the Yahoo Website to see all the historical transaction data necessary. However, after a certain point in the year, Yahoo removes access to the year’s information.

Luckily, in late 2009, Yahoo opened up their Fantasy Football API. Therefore, I was able to implement a .NET solution to retrieve the data I needed. Below are the steps I took.

The goal of our solution will be to create a simple ASP.NET Web Forms application that authenticates to Yahoo and then enables us to query the API.

Perhaps the most difficult hurdle to overcome is authentication. Yahoo uses a web standard called OAuth, which is a “simple, secure, and quick way to publish and access protected data”. You can find out more about it here, as I do not plan to delve into the low-level details of this protocol. The difficulty I found was that there are not many examples of .NET applications using this technology on the web.

To help us authenticate, we will leverage a .NET library called DevDefined OAuth.

  • Create a new Web Forms solution and add a reference to this project or compiled dll.

In our next step, we will create a simple button (named AuthenticateButton) in the Default.aspx page to kick off the authentication process.

  • Create a click event handler for your button. Enter the following code in the code-behind:

string requestUrl = https://api.login.yahoo.com/oauth/v2/get_request_token”;
        string userAuthorizeUrl = https://api.login.yahoo.com/oauth/v2/request_auth”;
        string accessUrl = https://api.login.yahoo.com/oauth/v2/get_token”;
        string callBackUrl = http://domain.com/Query.aspx”;

         protected void AuthenticateButton_Click(object sender, EventArgs e)
        {
            var consumerContext = new OAuthConsumerContext
            {
                ConsumerKey = “[provided by yahoo]”,
                SignatureMethod = SignatureMethod.HmacSha1,
                ConsumerSecret = “[provided by yahoo]”
            };

             var session = new OAuthSession(consumerContext, requestUrl, userAuthorizeUrl, accessUrl, callBackUrl);

             // get a request token from the provider
            IToken requestToken = session.GetRequestToken();

            // generate a user authorize url for this token (which you can use in a redirect from the current site)
            string authorizationLink = session.GetUserAuthorizationUrlForToken(requestToken, callBackUrl);

             Session[“oAuthSession”] = session;
            Session[“oAuthToken”] = requestToken;

             Response.Redirect(authorizationLink);
        }

 

To obtain your ConsumerKey and ConsumerSecret strings to place into the above code, go Yahoo’s Developer Projects Site and create a project. When creating your project, enter the Application URL (e.g. http://domain.com) and App Domain (e.g. domain.com) of the deployed location of your web site. Also, make sure to enable access to the Yahoo Fantasy Football API.

Take a look at the value in the callBackUrl string above. This needs to be edited to be an address on your web site. As part of the authentication process, Yahoo calls back to a URL on your site and therefore requires your site to be accessible from the public web.

  • Add a new web page to your project named “Query.aspx”
  • Place the below code in your Page_Load event handler

        protected void Page_Load(object sender, EventArgs e)
        {
            OAuthSession session = (OAuthSession)Session[“oAuthSession”];
            IToken requestToken = (IToken)Session[“oAuthToken”];

             // exchange a request token for an access token
            string oauth_verifier = Request.QueryString[“oauth_verifier”];
            if (!String.IsNullOrEmpty(oauth_verifier))
            {
                IToken accessToken = session.ExchangeRequestTokenForAccessToken(requestToken, oauth_verifier);
                Session[“oAuthSession”] = session;
            }
        }

 

Now that we are finished implementing the authentication code we can write the query submission logic.

  • Add a textbox (named QueryTextBox), a label (named ResultsLabel), and a button (named QueryButton) to the Query.aspx page
  • Add a click event handler for your button. Enter the following code in the code-behind:

        protected void QueryButton_Click(object sender, EventArgs e)
        {
            string query = QueryTextBox.Text;
            IConsumerRequest responseText = ((OAuthSession)Session[“oAuthSession”]).Request().Get().ForUrl(http://fantasysports.yahooapis.com/fantasy/v2/” + query);
            ResultsLabel.Text = responseText.ToString();
        }

 

You are now ready to query the Yahoo Fantasy Football API. Here is how you use it.

  1. Load the page by navigating to http://domain.com (replace “domain” with your website domain name).
  2. Click the Authenticate button

  1. Yahoo’s site will guide you through the steps to login to your Fantasy Football account and redirect to your site when finished.
  2. Enter an API Query into the text box and click “Submit Query.”

 

There are definitely improvements that can be made to our sample application. For instance, the results output from our query are not easily readable, but they can be simply output to an xml document or some other format for reading.

The amount of data that can be extracted from the API is huge and can be leveraged for some very creative purposes. For more information about the query syntax as well as available data, see the Fantasy Sports API Documentation.

You can download the code for the sample application.

 

Lastly, below are some resourceful links:

http://github.com/buildmaster/oauth-mvc.net

http://oauth.net/code/

http://oauth.googlecode.com/svn/code/csharp/

http://blog.techcle.com/2010/03/20/simple-oauth-integration-for-twitter-in-asp-net-mvc/

http://www.codeproject.com/KB/cs/Delicious-OAuth-API.aspx

http://code.google.com/p/devdefined-tools/w/list

http://developer.yahoo.com/fantasysports/

http://developer.yahoo.net/forum/index.php?showforum=122

 

5 Things I Hate about my Favorite Programming Language: C#

In episode 73 of the StackOverflow podcast , Jeff Atwood mentions one of his favorite questions to ask developers, “What are 5 things that you hate about your favorite programming language?”

It got me thinking. I definitely like some of the language features of C#, especially when developing within Visual Studio. Some of my favorites are Generics, Intellisense, and Short-Circuited conditionals. However, there are other pains that I encounter repeatedly when it comes to language syntax.

 

  1. In C#, there is the nifty syntax of following a variable with “??” allowing the developer to specify a replacement value in the case of the variable being null. In theory this is a great feature. However, I never end up getting to use this and I imagine that is the case for most developers. I find I usually end up using the “?” and “:” syntax because I typically want to use a member of the null object like “user.Identity.ToString()” but I have to check if “user” is null or I will get an object reference error.
  2. Why do I always have to lookup how to format a DateTime object in code without the minutes?
  3. If “ToString()” is a member of every object, why should I have to explicitly call it when setting the value of a string variable from another non-string variable? As an example, why can’t a string value be inferred from my int variable by just calling “ToString()” when there would otherwise be a type issue?


    int i = 0;

    string j = String.Empty;

    j = i;

  4. The compiler considers the use of “=” valid within an if condition. This can be confusing and often causes accidental issues where “==” is the intended code. As a solution, I use a coding standard of typing the constant value to be compared first because it cannot be assigned to (i.e. “if (0 == count)”).
  5. Nullable types seem like a great idea but they are not always intuitive. In the example below, the code seems like it should work. However, I receive a compiler error on the second line.


    int? i = null;

    i = (sender != null) ? sender.GetHashCode() : null;

 

Most of the above complaints were compiled off the top of my head. If you have found a better way to leverage the C# language so that you do not run into these issues, please share them with me in the comments. Perhaps it is my mis-use of the language features that has caused my agony.

I Heart Karnaugh Maps

Have you ever found yourself writing a long Boolean condition in your code like the line below?


if ((policy.Type == PolicyType.AutoInsurance && policy.PolicyHolder.PriorAccidents == 0) || (policyPaidInFull && policy.Type == PolicyType.AutoInsurance || policy.IsPremium) || (policy.Type == PolicyType.AutoInsurance && policy.PolicyHolder.PriorAccidents == 0 && policy.IsPremium))

 

I Heart Karnaugh MapsPerhaps that line of code above is the first and easiest way you thought about all the conditions that have to occur in your application’s business logic. You write that line of code, test it in many different scenarios and it works so you think you have done a good job. Well, there are ways to improve upon that line of code by removing logically equivalent Boolean expressions, not to mention some style improvements that might make it more understandable.

We owe gratitude to our dear friends the Electrical Engineers for developing a clever tool, named Karnaugh Maps, to help with this dilemma, usually for cases of no more than 6 variable conditions. Karnaugh Maps (pronounced “car-no” and often simply called “K-Maps”) are a system for reducing Boolean expressions into a more simplistic form. They originated from the need to reduce electrical wiring gates, or circuit minimization, but they are still useful for the high-level software developer.

 

Benefits of reduced Boolean expressions

  1. Increased program performance
  2. Increased readability of code
  3. Less code results in easier to change code

Reducing our example expression

The 1st step is to let letters represent each of the conditions in our expression. In our case:

  • a :     policy.Type == PolicyType.AutoInsurance
  • b :     policyPaidInFull
  • c :     policy.PolicyHolder.PriorAccidents == 0
  • d :     policy.IsPremium

Then, draw a graphical square like the one pictured below. This represents each possible combination of our Boolean conditions. The boxes are blank because we have not yet entered what Boolean results we want in our resultant expression.

Blank Karnaugh Map

Let’s take the first, simplified condition in parentheses, if (a && c), and put it into the map. The result would look like the below image, because we only need to fill in the boxes where a and c are both 1.

Sample Karnaugh Map

Following this example, we can use the entire Boolean expression to fill out the whole map. The completed Karnaugh Map is pictured below.

Completed Karnaugh Map

Now circle any square or straight line of boxes since they correspond to an expression that differs by only two bits.

Circled Karnaugh Map

Because of the way we have arranged our variables around the outside of the map, we can eliminate variables based on boxes filled with 1s being adjacent to each other. In our example, the vertical “circle” exhibits a scenario where the expression should always be true as long as both the a bit and the b bit are 1, hence the condition ( a && b ). Likewise, the square “circle” exhibits true cases whenever the c bit is 1 and the a bit is 1. Because the b bit and d bit are true no matter if their values are 0 or 1, they can be deleted from the resulting simplified expression, which would be || ( a && c ). We use a similar rule to find the final d condition.

In one sentence, this rule can be summarized as “the circled boxes can be grouped together and the two variables that differ can be discarded.”

The resulting Boolean expression is:

if ( ( a && b ) || ( d ) || ( a && c ) )

which, using Boolean algebra, can be further reduced to:

if ( ( a && ( b || c ) ) || ( d ) )

We were not able to completely remove any variables, but we did simplify the expression quite a bit. The original Boolean conditions can be substituted for our letter variables, and we can rewrite the original expression as below:


bool policyIsAuto = ( PolicyType.AutoInsurance == policy.Type );
bool zeroPriorAccidents = ( 0 == policy.PolicyHolder.PriorAccidents );
if ( policyIsAuto && ( policyPaidInFull || zeroPriorAccidents ) || policy.IsPremium )

Seems easy, right? It is. And I am sorry if my steps went too fast for you. My intention is not to teach how to use Karnaugh Maps for all circumstances but instead to show you how easy and useful it is to simplify your Boolean logic.

For help with different scenarios, find the book Bebop to the Boolean Boogie – an Unconventional Guide to Electronics at your local library, check out this Wikipedia link, or you can even download software to perform the rules for you.

Happy Karnaugh Mapping!

In the mean time, I hope I was able to show you how fun and easy using a system like this can be. Feel free to post questions in the comments.

 

– Karnaugh Map Images taken from Bebop to the Boolean Boogie – an Unconventional Guide to Electronics

– Digital Logic image created by Garrett Crawford

My First Experience with Microsoft Windows Azure

This week I received my Microsoft Windows Azure invitation token, so I began integrating it into a project of mine.  I wanted to use just the Blob Storage to upload and download large media files to the cloud.

At first, I was trying to follow this link as much as possible to get up and running.  The walk-through seemed simple and helped me to quickly understand how to use Blob Storage.  However, once I created the new Azure service in my existing solution I was quickly led to make decisions that influenced the web project I had already created:

  1. In order to get the Azure processes to run in the background while my web application ran, I had to set the Cloud Service project as the startup project. Set As Startup Project
  2. A Cloud Service project cannot just run by itselt, it requires a web role.  The simplest thing to do seemed to be to set this to my pre-existing web project.
  3. This all worked well at first.  My web project recognized my local azure service and worked normally.  However, once I tried to upload files to my local Blob Storage I received errors.  It behaved as if there was an issue with the Trust Level that the web role runs under.

Since Azure is still in CTP (meaning free) and I have a brand new account (meaning no pre-existing files have been uploaded), my solution was to test my web upload with a deployed, in “production”, Blob Storage service.  I updated my web.config file and fairly quickly was able to upload and download files from blob storage.  I was somewhat impressed with how easy it was to do.

Unfortunately, this created a whole new set of concerns.  Since I am forced to use my production account for Blob Storage, how can I test in my local environment going forward?  Once Azure is launched (reportedly on 02/01/2010), any testing I do will begin to incur significant costs and it will also interfere with production data.

After some deep thinking, some more research and stumbling across this MSDN link, I believe I backed my way into the solution that Microsoft imagined in the first place.

Microsoft has allocated a specific development shared key for local blob storage.  Therefore, one only has to use these standard configuration settings in the local Blob Storage service (ServiceConfiguration.cscfg file).

<ConfigurationSettings>
<Setting name=”AccountName” value=”devstoreaccount1″ />
<Setting name=”AccountSharedKey” value=”Eby8vdM02xNOcqFlqUwJPLlmEtlCDXJ1OUzFT50uSRZ6IFsuFq2UVErCz4I6tq/K1SZFPTOtr/KBHBeksoGMGw==” />
<Setting name=”BlobStorageEndpoint” value=”http://127.0.0.1:10000/&#8221; />
</ConfigurationSettings>

The piece of the puzzle that I was missing is that this Blob Storage service must run from outside my main solution.  Therefore, I put the Blob Storage service project in its own solution and attached it to a dummy web role.  When I run it, it starts the development Azure services and runs in the background.

Attaching to the Blob Storage service from my web project is easy.  I just make sure that I have the below configuration set in my web.config file.

<configuration>
<appSettings>
<add key = “AccountName” value=”devstoreaccount1″/>
<add key = “AccountSharedKey” value=”Eby8vdM02xNOcqFlqUwJPLlmEtlCDXJ1OUzFT50uSRZ6IFsuFq2UVErCz4I6tq/K1SZFPTOtr/KBHBeksoGMGw==”/>
<add key=”BlobStorageEndpoint” value=”http://127.0.0.1:10000″/&gt;
</appSettings>
<configuration>

Now I can test uploads and downloads on my local machine.

Special Note:  The Windows Azure development environment uses a different URI format to access files.  In production, files stored in public containers can be accessed via this format:

http://<account-name&gt;.blob.core.windows.net/<resource-path>

However, in the development environment, a different format is used:

http://<local-machine-address&gt;:<port>/<account-name>/<resource-path>

See this MSDN Article for more information.