Question: What's reflection, and how have you used it to solve a problem?

Answer: Reflection is a way to look at assembly metadata and look in and see what is contained. It also allows you to use late binding and call methods within those assembles.

For the second part, a simple explanation is all you need to show that you understand how it is used.

So what if you've enver used reflection? First, shame on you (kidding!). It DOES serve a very important purpose and allows for some great solutions, especially at an architectural level. If you've never used it, I recommend immediately trying it out, and you'll find many, many uses. Here's a tutorial I found that looks decent. That way, when asked this question (and I get this one a lot) you can answer how you *might* really use it. Honestly, you've probably used it and didn't realize it if you've added certain attributes to your code.

I have used reflection for everything from identifying certain classes and functions. For example, for a coding sample, I used LINQ for Reflection and attributes to identify classes which supported certain calculations. By doing this, I could add more functions dynamically and the UI would pick it without changing code. Since LINQ for Reflection is not discussed much, I'll post some about that later.

There are some costs associated with Reflection though. Speed! Late Binding is slower by it's nature, as well as all the processing looking for methods, so plan and use wisely!

As a full time developer, I search the web... a lot. If you are writing a lot of new code without at least searching to see what exists, you're either getting paid by the hour (or line of code), stubborn or a glutton for punishment. Even if I don't use it, I can get some guidance on what someone else tried, and how it worked out before I start coding. Granted, it usually requires a lot of refactoring the code to my standards or needs, but it's a great start.

As I was thinking of things I wanted to put on my site, I realized it would be nice to share my "favorites"...sort of. If I found something useful, I wanted to be able to show what it was, how I found it useful and where someone else can find it. In a way, I am also helping to promote someone else's hard work and improving their search engine visibility to return the favor of their sharing their work.

Out of this, I came up with an idea for a "Useful Links" section. I wanted to be able to add links and commentary, and also add it to my Activity Aggregator to show help show the content of the site has changed. Later, as I was using Bing, I got the idea to add some webthumbs to enhance the page graphically, so the reader would know what the site looked like before going there. I also needed to add an admin page for creating the useful links (and ultimately maintaining them -- which is on my TODO list). I'll also leave out the icon creation part, although I really need to farm out for a new cool looking icon, which is also on my list of things to do.

I'll skip the admin section, as it's just data entry fields. The process for creating the entries does change a bit, as I needed to do a few extra steps.

1. Save the UsefulLink class
2. Default the webthumb image to a default "safety" image in case we can't get a webthumb
3. Make a request to get a webthumb image of the target site
4. Once the image is retrieved, update the UsefulLink record to point to the new webthumb
5. Update the Activity Aggregator to show we have a new useful link.

Step 3 is where things get tricky. How in all getout do we get webthumb images? There are controls out there you can get, and they are reasonably priced as well. But I decided to keep searching so I could write this one on my own, as it seems like an interesting challenge.

My next thought was to create my own service to do this. There's plenty of code out there, but the easiest way to do this would require some WinForms programming. Don't get me wrong, I LOVE programming WinForms. The problem is I don't want to have to install it everywhere I am at, as I need a service. I could possibly create a Web and Windows service to do this as well, but that seemed overly complex. So I did a search, and I found this, which is a service which does it for you. What's even nicer is that they expose a nice API to use. As of now, the first 100 images a month are free, and after that, the fees are very reasonable. Even though I doubt I will go over 100 images per month, I am so impressed I may pay just to keep the service going.

I was also able to find some c# code to make learning the API fast. I did end up changing it some, but in general it worked very well. You can find it here.

So when the service returns with my image (I used the medium size), I save it to a thumbs directory (had to add write permissions to the directory, or I got an obscure GDI+ error), and call a method on my UsefulLink class to update the record with the thumbnail image. I name the image with the current date and time so that the names will be unique as well.

Finally, once I have downloaded the image and updated the UsefulLink record, I add a call to my Activity class which creates an entry for the Activity Aggregator. As I add more items to throw into the Activity Aggregator, I am considering refactoring things to do some delegate multicasting for all the updates, or perhaps creating a factory where you provide class (should be easy since my business objects share the same base class) or interface, and it knows how to create the activity record instead of making individual calls. That's on my list down the road. :)

Here's what the Activity Aggrgator looks like, with a special Useful Link icon():

And here's what the Useful Link section (which has the webthumbs) looks like. I will only be showing 10 at a time to save web page real estate. But I also don't want to lose older links off the page. I am debating now whether to use paging, or just have a smaller hyperlink-only section below the most recent links. I am leaning towards paging, as I have a very neat service I want to implement which makes paging and sorting incredibly fast and easy (more on that someday.. I need to upgrade it to user .Net 3.5 functionality before I post it).

I've been doing technical interviews for about 5 years now for .Net, and hired a lot of developers in that time. As a result, I have become proficient at quickly assessing a level of technical expertise as well as how a developer may fit within an organization. I will blog another time about what characteristics I look for in a candidate, but for now, I will go through some of the technical questions I ask, answer them, and explain why I ask the question.

Question: What's the difference between an abstract class and an interface

Answer: They have some similarities in that they both define abstract members which have to be implemented. An interface is really just a contract where you are stating "if I implement this interface, I will implement these methods". However, an abstract class can have an implementation, where an interface cannot. An abstract class can also have constructors and field data.

One advantage of an interface is that you can implement more than one interface per class, but you can only inherit from one class.

Note there's a lot more you could talk about with them both (and you don't want to overtalk any question), but the above will demonstrate you have a good knowledge of OOP design, which is what I was looking for. It's surprising how many developers cannot get this question right.

To learn more, here's a good article which discusses them in more detail (more than you'd need to answer the question for sure, but good knowledge to have!)

Decided to look at my web stats, and when I was looking at the search criteria people were using to find my site, I had to laugh at this one: hate llblgen

I wonder if someone else was at the point of frustration I was. All I can say is this -- don't blog about it!! :) I really ought to categorize this as a "Trick or Tip".

I needed to use LINQ to XML to grab some RSS feed information into a BusinessObject I created to save to a database. Here's what I needed:

I have to get some landscape rock put out before my home owner's association has a cow, but I decided to do some more work on my activity aggregator. Today, I decided to integrate my blog feed into it, so when I post here, it will automatically update this activity on my home page (and soon to be in my developer's area).

Here's what the end result looks (for now).

Doing it was fairly easy with the design I implemented in my last post. My BlogFeed class inherits the BaseFeed class, which means I need to implement the ParseFeed() method. Since the RSS feed from my blog is XML, I was easily able to adapt the same code from my TwitterFeed class to work for this RSS feed (which should actually work for any RSS feed I pass in).

I also created another Extension method (for practice) to convert the RSS feed date time to a C# DateTime object. I will post that code as "Tip of the Day" but I have to give Dan Wahlin credit for it, as I adapted some sample code he provided.

Here's how the RSS feed (aka BlogFeed) uses LINQ to XML for creating my activity object.

Tonight was a very enjoyable night of coding. I created the first phase of my "activity aggregator". I actually had a more clever name for it, but being tired, it slips my mind right now.

Currently, I post several places.. short updates for on Twitter. Longer discussions end up on here, my blog. I have some other sources I plan on integrating over time, such as links I found useful (similar to Digg, but also where I can place why I found it useful). That means growth, and when it comes to design, it's best to design change into it up front.

The first thing I needed to do was create my table and business object to collect these activities. In my table, I store ActivityDate, what type of activity it was (foreign key to another table -- ActivityType), a brief summary of the activity text, and finally the url someone interested could click on to get more information. The internal members of my activity class look like this:

Tonight I didn't get as much time to work on the site as I would have liked, so I focused on getting the admin pages up on the production server so I could do some "behind-the-scenes" work remotely. This required some security, which I started last night, but the data migration for that was a bit more daunting, so I needed to finish it tonight. While the authentication providers and controls do handle a LOT, it has an interesting learning-curve, and deployment can be a challenge as well. All-in-all, it sure beats writing all that code by myself.

I tried to use a lot of caching and cached settings to help improve the performance on certain pages, especially my client list. On my admin pages, I made sure to create a means to reset that cache without having to do a complete server reset. Actually, the same approach I took would work well for high availability sites, as the method I used to complete this would not require a server reset to re-load systems. When I was int he banking industry, high-availability was a huge issue, and simple config changes meant waiting for a scheduled system outage or worse, an emergency outage. When I redesigned that site, that was one of the top priorities I had.

It occurred to me how much time it takes to set up the infrastructure of a site: master pages, common libraries, configuration files, CSS, etc. Once those are done, if done properly, the rest of the site should go fast. One thing I have found to speed that up was the use of Visual Studio Project Templates. Combined with code generation like CodeSmith, you can really generate web sites extremely fast, and get on to coding the "fun" items. I will write about both of those in the future (CodeSmith and Project Templates) once the site is stabilized.

Tomorrow night may not have a lot of development, as my parents will be in town. Later this week, I will be coding my next control: the activity feed. When posts and feeds are made or read, this control will snag it, and place a brief "teaser" on the home page.

I finally managed to get my client list online today. From a technological standpoint, it was pretty straight forward. I store the information in the database, and use my CodeSmith templates to create a class for extracting the data, and then use a Repeater to present the information in a table format. I still need to make some changes to it, but all in all, it works well. Since the data won't be changing often, I did cache the data to make it come back faster.

I started working on security for my Administration pages. I need to get that set up before I can activate the admin pages, but I have run into some issues getting it all configured. I ran into this once before with the ASP.Net forms authentication security provider, but this time is a little different, as I only want to secure one folder. Certainly not too difficult to do, but not as easy as I would have hoped either.

Once I get the security and login page worked out, I'll begin working on my "links" page. The idea here is that when I blog, or post to twitter, or a few other ideas I have, it will update the dark blue control on the home page with a summary and hopefully someone will click through to get the rest of the details. This should be fairly straightforward to do. Since most of the services respond in XML, I'll just use a factory method to instantiate the proper object, which will know exactly what information I want to extract from the XML feed. As I add more items I want to track, I will simply have to implement the same interface and it will plug right in to my "updater". For the items which return XML (e.g. RSS or Twitter), I will use LINQ for XML to grab just want I want and populate the data right into my classes.

Which brings up a point...

I could probably do this almost as easy with XPath. When does it make sense to move to the more "sexier" technology as opposed something proven and works well? For example, a lot of times, when a new technology is rolled out, it tends to be buggy and some of them historically have not performed well (e.g. early XML for those who have been around a while). All things equal, when does it make sense? Just a rhetorical question, but one I got hit with recently.

I was in a technical interview for a job I wasn't planning on taking (drive was too far -- the company I was representing knew this as well, they just wanted me to be on their radar for the future). I was asked about a particular implementation of the new List object. Honestly, I know how to use the List object, and he was asking about some of the internals I really hadn't needed to know.

If I was having performance issues, I would want to know, and then I would look into it further. In this case, I was able to provide at least 4 other reasonable implementations based on the criteria I was given, yet, I still couldn't get the "sexy" answer he was looking for. At what point does it really matter? For my part, I didn't like NOT knowing, and I did look it up when I left, but in the big picture, when does it become relevant? In my book, the practical solution to a relevant problem always supercedes technical "sexiness".

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How the VS2008 IDE is very helpful to conditional compilation, and also how the site is coming along