Brendan Enrick

Daily Software Development

Silverlight Web Analytics: First Look

Anyone who has ever run a web site or a blog has probably taken a look at analytics packages to see who is visiting. I’ve recently been working on a very exciting project with Telerik, developing an application to provide this valuable information to bloggers and content creators.

To get things started we decided to tackle some of the basics first by asking these few questions:

  • “How many people are visiting my site?”
  • “Which locations drive the most traffic to my site?”
  • “What is my most popular content?”
  • “Who are the people visiting my site?”

From these simple questions we were able to start the application and get the cool demo set up that we were showing at the Telerik booth during PDC 2009.

The application is based around answering these four fundamental questions which are used to present the information to the users.

VisitorDashboard

Site Visit Information

RegionsDashboard

Regional Information

FavoritesDashboard

Most Trafficked Portions

ReferralsDashboard

Referring Locations

I had a great opportunity to speak with Todd Anglin about the project at PDC last month. My discussion of the Silverlight Web Analytics Application is available for viewing on Telerik TV. This demo of the application is a great way to see what we’re working on and give you an idea of what is coming soon.

Subscribe to my RSS feed and come back to read more as I will be posting about the architecture and some of the design decisions we made about the application.

A Quick Answer About Reference Types

Reference types were created to make dealing with pointers a little bit easier. They hide away the details of the pointers, so that the programmer need not think about them. In many ways I think they’re awesome, because they really achieve that goal. The problem is that by abstracting away the details of the pointers they’re sometimes difficult to work with, because they can be a little bit confusing.

I received a comment about this topic on one of my ASP Alliance articles explaining value types and reference types in C#.

First of all the article is excellent.
But why the following program produces output as:: abc:xyz
it should produce xyz:xyz.
I am confused...Plz help
The Code:
string myName = "abc";
string authorName = null;
authorName = myName;
authorName = "xyz";
Console.WriteLine("{0}:{1}",myName,authorName);
Console.ReadLine();
The Actual Output:
abc:xyz
The Expected Output:
xyz:xyz
as it's areference type only one copy is shared between references.

How about if we take this step by step looking at the variables and their values, and I’ll be able to explain why the behavior is as you’ve found. First here is the code we’ll be looking at.

string myName = "Brendan";
string authorName = null;
authorName = myName;
authorName = "Enrick";
Console.WriteLine("{0}:{1}",myName,authorName);
Console.ReadLine();

We are expecting it to print out “Brendan:Enrick”.

Red is for the variables and orange is for referenced values for those variables.

ReferenceTypes1

Notice that when we set a variable equal to a literal string value we get a new location in memory, but when we set it equal to another variable all we are doing is copying the pointer to that memory location. However, when we then set that variable equal to a new literal value it doesn’t replace the old one for both since they each had a pointer. It just creates a new location in memory with that value and assigns a pointer to that variable.

The type of behavior that the writer of this code was trying to achieve could be handled by pointers very easily, but reference types take away control of pointers. Loss of freedom for the sake of safety one might say. Now that I’ve said that everyone will switch back to using c++ to get their pointers back.

Thank you for asking the questions saurabh. I hope this thoroughly answers your question. If you have any more, please feel free to ask them as well.

Expression Blend Issue with Abstract Base Classes

Earlier, I wrote a post about using inheritance with Silverlight UserControls. The post shows really quickly how one can have their UserControl inherit from another class. One tip I’ll mention is that the base class can be abstract, but not if you plan on using Expression Blend. Generally if you have a class which shouldn’t ever be instantiate, you should make it abstract.

The issue is one that I discovered, much to my annoyance, the hard way. As it turns out Expression Blend is currently unable to give a preview of a UserControl that is inheriting from an abstract base class. When you open one of these in Blend you’ll get the Red Box of Death and in it is a message stating, “Exception: Cannot create an instance of “MyClass”.

Not exactly very helpful, but it does at least point you to the fact that there is something wrong with your base class. If you run into this make sure you know that you cannot use a base class. I believe that Blend requires a default constructor, and an abstract class has no constructors.

Solution 1

If you have control of the abstract class, you probably just want to make it a concrete class and hope no one is dumb enough to use it as a concrete class. This is actually a good place for a comment so you have a reminder of why the class is not abstract. Otherwise you might make it abstract again. The comment will also tip someone off that they can make it abstract if Blend ever supports this.

Solution 2

If you don’t have control of the abstract class, perhaps because it is in a class library you’re referencing, you will want to place a concrete class between your class and the abstract. This new class will be the one you specify in your XAML and is thus used by Expression Blend. This one adds an extra layer which really adds nothing and could cause confusion, so I would lean towards the other solution.

Silverlight UserControl Inheritance

One way in which we object-oriented developers try to achieve code reuse is by using inheritance. This allows us to have shared functionality in one place. Awesome we all know how to do this and it’s easy right? Try it in Silverlight for your UserControls. It is a little bit more challenging.

The problem we have is that we’re working with partial classes and these classes are trying to make things difficult for us. One of them is the noticeably declared one in the code behind file. The other one is created from the XAML file. The XAML file declares the base class it is inheriting from. In this instance it is the UserControl class.

Here are the steps required to use a different base class for your UserControls in Silverlight.

1. Create a class inheriting from UserControl and add your desired extras to the class.

2. Create a normal UserControl class and change the base class in the XAML file. You will need to declare an xml namespace for the namespace your base class is in, and use that namespace when declaring the base class.

<UI:MyBaseClass x:Class="MyProject.UI.UserControls.ConcreteImplementation"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:UI="clr-namespace:MyProject.UI" 
    Width="400" Height="300">
    <Grid x:Name="LayoutRoot" Background="White">
 
    </Grid>
</UI:MyBaseClass>

3. Change the inheritance in the code behind (.cs or .vb) file so that it is using the new base class. [Optional – Because of the way partials work you don’t need to declare this one as inheriting from the base class, but it does make things more obvious for someone using the code.]

Enjoy using your base class in Silverlight.

Working with Interfaces - Practical Uses

Expanding on an article I wrote a couple of years ago where I explained interfaces in C#, I’d like to explain why people should use interfaces. I received an email from a reader of my ASP Alliance article. He understands how interfaces work, but he’s trying to see why so many people are raving wildly about their greatness. His questioning of them is great, because it really is not obvious why interfaces are useful. Anyone who says otherwise is just trying to brag.

A couple of years ago, you wrote an article for ASP Alliance called "Understanding Interfaces." Once again, I saw how the code works, once again, I failed to see how it will benefit me.

Here's where everything breaks down for me: You create an interface with just method, property and event signatures. Then you inherit them in a class, recreate these same signatures and write the code to implement these methods and properties.

So I’ll start by mentioning that nearly all patterns, practices, principles, etc. in software development are based on code reuse. One of the most important reasons for code reuse is change. Developers are always responding to and creating changes. We must mitigate the risks of change, identify where changes will occur, and we must make changes.

Right about now you might be thinking, “but interfaces don’t reuse code. They just force you to implement new code. Using inheritance would be the way to achieve code reuse.” You ate technically correct. You understand how interfaces work, but you’re not seeing why we use interfaces. Interfaces themselves do not give us code reuse at all, however, they enable us to achieve code reuse.

Remember that I said that we must identify where changes will occur. Making this identification allows us to isolate changes thus mitigating the risks of changes and allowing us to make changes. Isolating the places that change also allow us the reuse the code which does not change, so by keeping some parts separate we can reuse others. The interfaces are for the places we can’t reuse the code.

Interfaces are “places of change”. Each implementation of the interface is a variation on how that required piece of the puzzle could have been implemented. This is contrary to how you’ll see a lot of interfaces used. It is sometimes difficult to see this as the behavior of interfaces, because people overuse interfaces.

As I see it, I could have saved a whole lot of time by not creating the interface in the first place! I mean, it's not doing any work. I still have to create the signatures in the class. Why on Earth do people praise these things and call them the answer to multiple inheritence? They don't do anything!

It is mostly true that interfaces don’t do anything. As far as being executable code is concerned an interface is basically just a worthless extra step, so why would we use them? Declaring an interface is like saying, “there is more than one way that this behavior could be implemented, but interactions with this behavior should be done this way only.” Having that common “interface” allows us to use any of these implementations interchangeably.

When to Use Interfaces

Some people would recommend that interfaces should be used everywhere. I’ve heard people say that no variable should be declared with a concrete type if it can be avoided. That may be a valid point, but if you’re just learning how interfaces can be useful that is a bad approach. If you don’t see value in interfaces, you will certainly not see the value of them when people use them everywhere. This washes them out and obfuscates their purpose.

Interfaces are used for logic which will have multiple or changing implementations. This means that we should use them in places where we will out of necessity have duplicate logic. Using the interface is what allows us to do this. Take a look at this code for composing a letter.

public string ComposeLetter(string recipientName, 
string messageBody, bool isFormal)
{
string messageText = string.Empty;
if (isFormal)
{
messageText += GetFormalGreeting(recipientName);
}
else
{
messageText += GetCasualGreeting(recipientName);
}

messageText += messageBody;

if (isFormal)
{
messageText += GetFormalSignature();
}
else
{
messageText += GetCasualSignature();
}

return messageText;
}

Notice how we have these flow control operators dictating how the code will execute. What will happen if we need to have a third option for greetings and signatures for family members? We might add another else-if or we might use a switch. Either way this code gets larger and changed every time.

However, if we identify the aspects of the code that are changing we can isolate them and mitigate the risks of changing the code by keeping separate the logic which has multiple implementations. Notice we have already used one form of encapsulation by keeping each of those pieces of logic in separate methods. The logic we haven’t encapsulated is the flow control.

We can create an interface for it. The best name I’ve got for now is IFormalityGenerator, which is not a great name, but it will do for now. I’ll create that interface with two methods: GetGreeting and GetSignature. Very simple interface. Now we can rewrite our method to look like this.

public string ComposeLetter(string recipientName, string messageBody, 
IFormalityGenerator formalityGenerator)
{
string messageText = string.Empty;

messageText += formalityGenerator.GetGreeting(recipientName);

messageText += GetMessageBody();

messageText += formalityGenerator.GetSignature();

return messageText;
}

We now just make the decision sooner and only once which implementation we are using. If this is a formal letter we will use the FormalFormalityGenerator. If it is casual we will use the CasualFormalityGenerator. Down the road when we create one for family members we can just go and create an implementation for the FamilyFormalityGenerator. We’ve made it so we create new code each time instead of going and changing the existing code in this method.

The power of an interface is in its ability to encapsulate the volatile aspects of a program and isolate that which can be reused more easily.

Users Don't Read Your Text

A few days ago Jeff Atwood wrote a great post about users. This is my post adding to his.

I also develop applications, and user interfaces is a common topic of discussion. The interface of an application is one of the most important aspects of it. What a lot of people seem not to realize and Jeff nicely highlights is that users don’t read anything. Trust me. I use a lot of applications, and I avoid reading anything that is more than six or seven letters long.

If I have to read something to use an application you’re probably going to lose me. I am not here to learn your application I am here to use your application. Jeff shows this image as what a user sees on Stack Overflow when writing a question.

su-ask-what-the-user-sees

I think he is a little bit off here. Why? Oh I don’t know, because he includes the preview. I might look at the preview, but only if I am concerned about how something is formatted. If I don’t think I did anything complicated I don’t bother checking the preview. I figure I should be able to use this page while only really reading this section.

su-ask-what-the-user-really-sees

When I need to reference something I will find it on the page. However, the 90% case is going to be this. I’ll make a decision if I need to look elsewhere, and I’ll be annoyed when I have to.

I use Stack Overflow and I think the interface is great Jeff. You support standard keyboard shortcuts, so I can learn what they do and how to format them by only observing the editor and occasionally the preview section. When I need a list I know to use the buttons at the top. Anything that is a standard convention I will follow. You give me a toolbar of choices and keyboard shortcuts and I’m set.

I think it is most important to follow common practice if you want things right. I am not sure why people have such trouble with Stack Overflow’s editor.

Working with the Default Layout of Silverlight RadCharts

The default layout for a RadChart works for most situations. It has a ChartArea, a ChartLegend, and a ChartTitle. These are easy to work with, and if you want you can break from the norm and create your own custom Silverlight Rad Chart layout. If you’re sticking with the default you almost certainly have some settings and properties to which you will want to make adjustments. In order to do that you might define these in the XAML.

<UserControl x:Class="MyApplication.UI.Charts.SuperSweetChart"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:telerikChart="clr-namespace:Telerik.Windows.Controls;assembly=Telerik.Windows.Controls.Charting" 
    xmlns:chart="clr-namespace:Telerik.Windows.Controls.Charting;assembly=Telerik.Windows.Controls.Charting" 
    Width="400" Height="300">
    <Grid x:Name="LayoutRoot" Background="White">
        <telerikChart:RadChart x:Name="Chart1" 
                               Loaded="Chart1_Loaded">
            <telerikChart:RadChart.DefaultView>
                <chart:ChartDefaultView>
                    <chart:ChartDefaultView.ChartArea>
                        <chart:ChartArea LegendName="CustomLegend" NoDataString="">
                            <chart:ChartArea.DataSeries>
                                <chart:DataSeries x:Name="DataSeries1" >
                                    <chart:DataSeries.Definition>
                                        <chart:PieSeriesDefinition 
                                            LabelOffset="0.6d" 
                                            ShowItemToolTips="True" 
                                            ItemToolTipFormat = "#XCAT" 
                                            DefaultLabelFormat = "#%{p0}" />
                                    </chart:DataSeries.Definition>
                                    <chart:DataPoint YValue="35" />
                                    <chart:DataPoint YValue="15" />
                                    <chart:DataPoint YValue="55" />
                                </chart:DataSeries>
                            </chart:ChartArea.DataSeries>
                        </chart:ChartArea>
                    </chart:ChartDefaultView.ChartArea>
                    
                    <chart:ChartDefaultView.ChartLegend>
                        <chart:ChartLegend x:Name="CustomLegend" 
                                           UseAutoGeneratedItems="True" />
                    </chart:ChartDefaultView.ChartLegend>
                    
                    <chart:ChartDefaultView.ChartTitle>
                        <chart:ChartTitle>
                            <TextBlock Text="Traffic Sources"/>
                        </chart:ChartTitle>
                    </chart:ChartDefaultView.ChartTitle>
                    
                </chart:ChartDefaultView>
            </telerikChart:RadChart.DefaultView>
        </telerikChart:RadChart>
    </Grid>

Notice the three parts are the ChartArea, the ChartLegend, and the ChartTitle. Use the properties of these to make your adjustments. If you don’t want to change these in the XAML then don’t include them. If you’re going to work from the code behind it doesn’t hurt to have these here, but it can be useful.

You can access these in the code behind by either declaring their x:Name property or by referencing them from the RadChart’s x:Name like this. Chart1.DefaultView.ChartArea.

Plus keeping things in here keeps designers happy, and we design-challenged people really appreciate happy designers willing to assist us.

Implementing IEnumerable and IEnumerator

Working with a foreach loop is the primary reason to implement the IEnumerable and IEnumerator interfaces. You’ll want one of each of these to work with the loop.

I am going to do an example DateRange class which will implement IEnumerable<DateTime> and will allow us to iterate through a non-existent collection of DateTime objects.

Note: I am aware of the fact that I could achieve the same result with a for loop. I find the foreach loop more readable.

First we need to create a basic DateRange class. A range can be defined as a StartDate and an EndDate, so I’ll start there.

public class DateRange
{
    public DateRange(DateTime startDate, DateTime endDate)
    {
        StartDate = startDate;
        EndDate = endDate;
    }
 
    public DateTime StartDate { get; set; }
    public DateTime EndDate { get; set; }
}

So this DateRange could be useful on its own, but we want to be able to iterate this collection using a foreach. So to start we need to implement the IEnumerable<DateTime> interface.

public class DateRange : IEnumerable<DateTime>
{
    public DateRange(DateTime startDate, DateTime endDate)
    {
        StartDate = startDate;
        EndDate = endDate;
    }
 
    public DateTime StartDate { get; set; }
    public DateTime EndDate { get; set; }
 
    public IEnumerator<DateTime> GetEnumerator()
    {
        return new DateRangeEnumerator(this);
    }
 
    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

 

Notice here that we now need to get the IEnumerator<DateTime> object in the GetEnumerator() method. I jumped the gun a bit and I’ve called a class that doesn’t exist yet. I’ll make another class and implement the required methods for the IEnumerator interface.

public class DateRangeEnumerator : IEnumerator<DateTime>
{
    private int _index = -1;
    private readonly DateRange _dateRange;
 
    public DateRangeEnumerator(DateRange dateRange)
    {
        _dateRange = dateRange;
    }
 
    public void Dispose()
    {
    }
 
    public bool MoveNext()
    {
        _index++;
        if (_index > (_dateRange.EndDate - _dateRange.StartDate).Days)
            return false;
        return true;
    }
 
    public void Reset()
    {
        _index = -1;
    }
 
    public DateTime Current
    {
        get { return _dateRange.StartDate.AddDays(_index); }
    }
 
    object IEnumerator.Current
    {
        get { return Current; }
    }
}

 

These are the handful of methods we implement for the IEnumerator<DateTime> interface. These are all about moving to the next object and getting the current object. Resetting and Disposal of the object are less important, so make sure you read MoveNext and Current.

Keep in mind here that I could have used a collection for this, but I didn’t because I don’t need one. The calculation to get the items was easy enough.

var dateRange = new DateRange(DateTime.Today.AddDays(-6), DateTime.Today);
foreach (DateTime date in dateRange)
{
    Console.WriteLine(date.ToShortDateString());
}

Output:

10/20/2009
10/21/2009
10/22/2009
10/23/2009
10/24/2009
10/25/2009
10/26/2009

Visual Studio 2010 Beta 2 is Here

As of today Visual Studio Beta 2 is available to the general public. There is a VS 2010 Beta 2 iso available for download. It has some really nifty features. I’ve been playing around with it.

First off I will say that it actually looks very cool.

StartPage

I think they did well. The new start page here is also a lot cleaner. I’ll be looking to see how to customize it a little.

Creating new projects is a lot better. Far less intimidating in this new default view. If they can keep the clutter down on this I will be very happy.

NewProject

So I created an “Empty ASP.NET Web Application”. I noticed one crazy thing about it. I don’t think there are enough references here? Maybe we need more. C’mon guys. Seriously. Who wants to start with all of these in there? I chose the “Empty” one so I wouldn’t have all of this clutter.

StandardReferences

But wait! They did remove the clutter. Guthrie had mentioned they were doing this. I am just now seeing the web.config and it is AWESOME!

DefaultWebConfig

There is barely anything in the web.config. Yipee! Hooray!

“Navigate To” is a nice feature. I already use ReSharper, so the wow factor is gone. I am glad to have it integrated though.

NavigateTo

We were able to move the editor window around in previous versions of Visual Studio, but this feels a lot nicer, and anyway it’s still useful. Grab an editor window and decide where to put it. Much more freedom for splitting the screen this way.

 

MoveEditorWindow

You can do stuff like this. And have three editors open at once (you better have a lot of screen real estate before you try this).

TiledWindows

Or if you actually use the designer in Visual Studio you can split it along with the code behind file. Getting you the Design, Source, and Code Behind.

TileWithSplitView

This looks like a pretty nice thing they’ve build here. I figured with the big changes they were making that this version of VS would be lacking in too many upgrades. It seems they’ve managed to pull off some nice stuff here.

I am sure I’ll discover more new stuff at some point. Luckily the same feel is here, so just need to learn all of the little changes and additions.

When Should You Comment Your Code

Comment your code when it is hard to understand or determine your intent, because your code is crap. Yep, that is pretty much the best time to comment your code. When I was in college I was told to make sure that I commented my code. I always wondered why. Now I know. Comments really tended to clutter things and make it less clear what I was trying to achieve. I’ve written plenty of comments, but I know that when I use a comment that it means my code sucks.

Comments take time to write, they take up valuable space, they add clutter, and they’re often out of date. So why do we write them? We write them because there is something confusing about some code. Or something that we need to tell future readers about the code.

I very much enjoy being reassured of the way I do things by the books I read. I’ve been reading Code Complete, and it makes me glad they I blatantly disagreed with the people who told me to comment my code. Why? Because the author of the book tells me the exact opposite. I’ve often used the phrase, “code should be self-documenting.” I am not sure from whom or from where I first heard that, but it also affirmed my belief about comments.

The proper use of comments is to compensate for our failure to express ourself in code. Note that I used the word failure. I meant it. Comments are always failures. We must have them because we cannot always figure out how to express ourselves without them, but their use is not a cause for celebration.

Aside from the misuse of the English language, that is an excellent paragraph. I’ve never liked writing comments, and I doubt I ever will. It is interesting how some programmers swear by them. I think they are the same programmers who use single-letter variables, magic numbers, and hundred line methods.

I highly recommend reading through the best comments in source code question on StackOverflow.

Remember kids, anytime you feel the need to write a comment, fix your code instead. You’ll thank yourself down the road. You might be the future developer maintaining the code.

A few steps to follow. (These are the easy ones. Harder ones take more than a bullet point to explain and justify.)

  • Rename variables to more expressive names.
  • Extract methods so people know what you’re doing.
  • Extract classes to handle each responsibility.