Tag Archive for 'CodeProject'

A .NET Application that Never Dies

29392-Live_forever_-sfullJeremy’s Graceful Shutdown Braindump should really include another use case. How do you create a .NET application that never shuts down? Ever!

This  is a common scenario for closed systems that only allow the user to interact with a predefined set of applications.  In other words, the user is never able to utilize any of the operating system functionality. In particular, they can not install new applications or update any software components.

This situation is related to the issues discussed in Medical Device Software on Shared Computers. Creating a closed Windows-based system is not an easy task. For our XP Embedded system here are some of the considerations:

  1. Prevent booting from a peripheral device (CD-ROM, USB stick, etc.)
  2. Prevent access to the BIOS so that #1 is enforced.
  3. Prevent plug-n-play devices from auto-starting installers.
  4. You can not run Explorer as the start-up shell — no desktop or start menu.
  5. Prevent Ctrl-Alt-Del from activating task manager options.
  6. Disable the Alt-Tab selection window so the user can not switch application focus.
  7. Ensure that the primary user interface application is always running.
  8. All UI components must exit without user interaction when the system is powered down.

One of the challenges for .NET applications is how to handle unexpected exceptions. What you need first is a way to catch all exceptions.  OK, so now you know your program is in serious distress. You may be able to recover some work (a la a “graceful shutdown”), but after that it’s not a good idea keep the application running.

That means you have to restart the program. For a WinForm application one option is:

Application.Restart() essentially calls Application.Exit() which tries to gracefully shutdown all UI threads.   The problem with that is the application may appear to be hung if you have background worker threads that are monitoring hardware devices that are not currently responding.

Another issue is when the .NET application is doing interop with COM components.  I’ve seen situations where all of the managed threads appear to exit properly via Application.Exit() but an un-managed exception (and error window) still occur.  This behavior is unacceptable.

The way to ensure that the application restarts properly (simplified):

The Environment.Exit() call is harsh, but it is the only way I know of that guarantees that the application really exits.  If you want a Windows Application event log and a dump of your application you can use Environment.FailFast() instead.

UPDATE (9/19/09): I ran across a post about COM object memory allocation in mixed managed/unmanaged environments: Getting IUnknown from __ComObject. As this article exemplifies, debugging COM objects under these circumstances is a real pain in the butt.  We used strongly-typed managed wrappers for our COM objects. Besides a .NET  memory profiler we just monitored overall allocations externally with Process Explorer. It may be undocumented and fragile, but at least it’s good to know that there is way to dig deeper if you need to.

Cloud Computing Design Patterns

I attended some talks this weekend at the SoCal Code Camp.  Since I’ve been exploring cloud computing lately, the David Pallmann talk on Azure Design Patterns was of particular interest.

The Azure Design Patterns site gives an overview of the Azure services (“Core”), but it was the composite applications that combine these core functions that provided the most insight regarding potential cloud applications.

For example the Hosted Web Service with Background Workers is depicted like this:

Hosted with Background Workers

Dave spent a majority of the talk on Azure core services.   The differences and similarities between Azure and Amazon Web Services and Google App Engine were easy to identify.

The Azure core services are interesting, but I would have liked a more thorough investigation of these application patterns and their implementation details. There was just too much material to cover in a 1.5 hour talk.

It’s easy to see how many of these application patterns could be implemented in either AWS or GAE.  Understanding a pattern’s pros and cons in the context of any of the available cloud computing solutions is critical when you’re considering an architecture.

I haven’t been able to find  similar design documentation by AWS or GAE. They only cover their core service APIs and provide white papers on how specific applications are constructed.

Kudos to Dave for the great talk and putting together these useful descriptions and code samples.

UPDATE (11/25/09): Cloud Computing Patterns

Plunging into Web Development

ConanI’ve authored a few web sites. Nothing professionally though. I know just enough HTML, CSS, and JavaScript to be dangerous.

Now I’m faced with creating a customer-facing site that has (or will someday soon have) real requirements.

Here are a couple of the requirements I know so far:

  1. Relatively low volume traffic. The site will be public, but only registered users (customers) will have access.  No product pages, no shopping carts, no ads, no social networking. The front page is a login screen.
  2. Reliable and secure transport and storage of medical data.  At a minimum we must comply with HIPAA standards (privacy rules).

I don’t see web site development as really that different from building any other type of application. It’s all software. The architectural building blocks may be different, but the developer’s mind-set and methodologies for producing a quality product need to  be the same.

I haven’t gotten far enough along to really understand all of the deployment and maintenance issues. I’m thinking about them though. The same goes for testing. I can foresee development vs. production platform testing issues that will have to be carefully considered.

What I want to do is walk you through my rational for the selection of some of the major components and tools I’m considering using for this project.

Web Frameworks

Here’s a little historical perspective on selecting a web development framework:


Yep, that’s how it feels.  There are at least 100 options (plus a couple of my additions):

AgaviAIDA/Web | Ajile | Akelos | Apache ClickApache CocoonApache StrutsApache WicketAppFuseAraneaASP.NET MVC | Axiom Stack | BFCCakePHPCampingCatalystCherryPyCodeIgniterColdSpringCSLACppCMSDjangoDotNetNukeDrupal | ErlyWeb | eZ ComponentsFlex | FUSE | FuseboxGoogle Web ToolkitGrokGrailsHamletsHordeInterchangeItsNatIT Mill ToolkitJavaServer Faces | Jaxer | JBoss SeamKepler | Kohana | Lift | LISA | ManyDesigns PortofinoMasonMaypoleMach-IIMerbMidgardModel-GlueMonoRailMorfikNitroonTapOpenACSOpenLaszloOpenXava | Orbit | PEAR | Orinoco | PyjamasPylonsQcodoRadicoreReasonable Server FacesRIFERuby on RailsSeasideShale | Simplicity | SilverStripe (Sapphire)SmartClientSofiaSPIPSpringStripesSymfonyTapestryThinWire | Tigermouse | VaadinTurboGearsWavemakerweb2pyWebObjectsWebWork | Wigbi | YiiZendZK | Zoop | Zope 2Zope 3ztemplates


As a .NET developer, my first inclination was to look at ASP.NET MVC. The two most popular and active open source frameworks are  Ruby on Rails (RoR) and Django (Python-based). To be honest, I have not spent a lot of time investigating any of the others.

Why is it that I often find myself in this situation? It’s usually not 100, but there always seems to be multiple well developed solutions for these types of problems.  I ran into the same thing a couple of years ago when I was selecting an ORM for a .NET project.

All you can do is start by taking the advice of others (“most popular”) and give one or two a try.  Not only will you get a good sense of how well the framework meets your project requirements, since there will inevitably be problems or questions you’ll also be able to evaluate documentation and community activity.

It’s like making pasta — you throw a noodle against the wall and if it sticks, you’re done cooking.  Well, not really… but you know what I mean.


One of the major considerations is hosting. I’ve previously explored the three major cloud computing platforms.

  • Amazon EC2 would be overkill (see requirement #1). I don’t see a need for significant scale-up in the foreseeable future. Running a small on-demand EC2 instance 24/7 is more expensive (~$70/month) than just buying hosted services.  Also, supporting a complete OS platform is unnecessary work.
  • Microsoft Azure is currently in CTP (Community Technology Preview) and it’s still unclear what the pricing will be.
  • That leaves Google App Engine.  Based on the GAE Quotas, we would be able to operate under the limits for quite a while (exceeding the quotas would be a good thing).  That means GAE can provide us free hosting, which is hard to beat.

There are literally 100’s of hosting options, and most would meet our bandwidth and storage requirements at a nominal cost.  Independent of storage (see below) I guess I’m biased towards a cloud solution for two reasons:

  1. “Good Enough” isn’t Good Enough: I’ve been hosting this domain on a commercial site for about 6 years.  I’d classify my host as good enough for my personal use (family site, photo gallery, this blog, etc.).  If my hosting service went away tomorrow, no big deal. I backup everything regularly and could be up and running on a comparable host pretty quickly. But for business purposes that involve critical customer medical data, “good enough” and the possibility of the host disappearing just doesn’t cut it.
  2. Large Infrastructure: This is what makes a cloud solution so attractive. With any of the three cloud options you are buying into reliability and stability. They already have multiple data centers, security, and disaster plans in place.  You don’t have to worry about Amazon, Microsoft, or Google going away any time soon. Unless you have the resources to build it yourself, IMO using a cloud service is a good business decision.

So for now I’ll be using Google App Engine.

Data Storage

Now lets looks at requirement #2: reliable and secure data storage. At this time the best solution seems to be Amazon S3. Amazon has already put a lot of thought into this:  Creating HIPAA-Compliant Medical Data Applications with Amazon Web Services (warning: PDF).  S3 transfer and storage costs are very reasonable.  Paying only for what you use is a real benefit.

Both Google and Microsoft are very active in the Healthcare sector (Google Health and HealthVault) and I’m sure will soon have cloud storage offerings with similar features.

There are a number of web hosting sites that claim HIPAA data storage compliance, but most seem to just be using “HIPAA” as a marketing tool to attract medically related clients. I’d stay away from these.

Web Frameworks (part 2)

Deciding to use GAE quickly narrows the web framework choice down. GAE supports Python (w/ Django) and the Java 6 runtime environment. I do not believe that either ASP.NET or RoR are supported on GAE. Done deal — Django.

I know what you’re thinking.  There are many other Python-based web frameworks and even Java alternatives that I should be considering. That’s true, but Django is arguably the most popular and has a very active developers community. Also, there are several Google Code App Engine projects (see below) that support Django integration.

I did play around with RoR . The Ruby language itself is great. I love having five different ways to do the same thing. The RoR web framework is mature and has many of the same features as Django.

I looked at ASP.NET MVC, but only from a distance. Here’s a concise take from someone that recently jumped in: ASP.NET MVC Impressions after 1 week.

Development Environment

I initially setup a Windows-based Python/Django/GAE-SDK development environment but found it to be too clumsy.  I’ve settled into Ubuntu 9.04 running in a VirtualBox VM.

The Ubuntu Package Manager handled installation of all the necessary prerequisite components. Now that I think of it, I didn’t have to do a single ./configure and make. That’s progress!

I’m an old Unix hack and I quickly fell back into my first love : Emacs. After the nostalgia wore off, I needed to find a real development IDE.  There were two choices:

  1. Eclipse:  I tried using the PyDev plug-in along with some Django integration instructions I found. Google also provides some Eclipse integration, but being able to start the server and other functions from the IDE was not that important to me.  I’d rather use the command line. Also, Eclipse just seems like a real dog.
  2. Netbeans:  With the Python plug-in Netbeans works fine, so I’ll stick with it until something better comes along.

Django (Front-end)

The four features that make  Django attractive:

  • Object-relational mapper: Define your data models entirely in Python. You get a rich, dynamic database-access API for free — but you can still write SQL if needed.
  • Automatic admin interface: Save yourself the tedious work of creating interfaces for people to add and update content. Django does that automatically, and it’s production-ready.
  • Elegant URL design: Design pretty, cruft-free URLs with no framework-specific limitations. Be as flexible as you like.
  • Template system: Use Django’s powerful, extensible and designer-friendly template language to separate design, content and Python code.

Carefully walk through the four part Django tutorial. Beware: there are three versions of the tutorial (0.96, 1.0, and “Latest”). Make sure you’re using the desired one.

For Django integration with GAE I’m using app-engine-patch.  I had first tried Google App Engine Helper for Django, but I found that app-engine-patch works much better.

Data Integration (Back-end)

Getting data to and from the S3 server will be a critical component.  I have only started looking into this, but the Amazon documentation seems very good.  The Getting Started Guide examples are presented in multiple languages (PHP, C#, Java, Perl, Ruby, Python).  A Python interface to Amazon Web Services, Boto, also looks like it might be useful.

Amazon S3 POST is an efficient way to move data to S3:

S3 Post

The back-end will require much more investigation.

For the additional database needs (account management, logging, auditing, etc.) I’ll just use the GAE Datastore.


There’s a lot of “stuff” here. Investigating and evaluating it all plus making decisions is a daunting process.

The purpose of going through these selections is to reduce the number of variables so I could start concentrating on an architecture and design that will meet project requirements. There are still many unknowns though, and I’m sure there will be major bumps in the road that will cause me to change direction.

UPDATE (11/21/2010): Beware — you get what you pay for!: Goodbye Google App Engine (GAE)

Continuous Learning: 14 Ways to Stay at the Top of Your Profession

Professional development refers to skills and knowledge attained for both personal development and career advancement. ” I’m fortunate in that my personal and career interests are well aligned. I must enjoy my work because I do a lot of the same activities with a majority of my free time (just ask my wife!).

Keeping up with an industry’s current technologies and trends is a daunting task.  Karl Seguin’s post Part of your job should be to learn got me to thinking about the things I do to stay on top of my interests.  I never really thought about it much before, but as I started making a list I was surprised by how fast it grew.  When it reached a critical mass that I thought it would be worth sharing.

I actually have two professions. I’m a Biomedical Engineer (formal training) and a Software Engineer (self proclaimed).  I primarily do software design and development, but being in the medical device industry also requires that I keep abreast of regulatory happenings (the FDA in particular, HIPAA, etc.), quality system issues,  and industry standards (e.g. HL7).

Keeping track of Healthcare IT trends is also a big task. With the new emphasis by the federal government on EMR adoption, even a small company like mine has started planning and investing in the future demand for medical device integration.

The other major topic of interest to me is software design and development methodologies. A lot of the good work in this area seems to come from people that are involved in building enterprise class systems. I’ve discussed the ALT.NET community (here) and still think they are worth following.

So here’s my list.  I talk about them with respect to my interests (mostly software technologies), but I think they are generally applicable to any profession.

1. Skunk Works

Getting permission from your manager to investigate new technologies that could potentially be used by your company is win-win. In particular, if you can parlay your new-found skills into a product that makes money (for the company, of course), then it’s WIN-WIN.

In case you’ve never heard this phrase:  Skunk works.

2. Personal Projects

I always seem to be working with a new software development tool or trying to learn a new programming language. Even if you don’t become an expert at them, I think hands-on exposure to other technologies and techniques is invaluable. It gives you new perspectives on the things that you are an expert in.

Besides getting involved in an open source project, people have many interesting hobby projects.  See Do you have a hobby development project? for some examples.

3. Reading Blogs

I currently follow about 40 feeds on a variety of topics. I try to remove 2-3  feeds and replace them with new ones at least once a month. Here is my Google Reader trend for the last 30 days:

30 day RSS trendYou can see I’m pretty consistent. That’s 1605 posts in 30 days, or about 53 posts per day. To some, this may seem like a lot. To others, I’m a wimp.  During the week I usually read them over lunch or in the evening.

4. Google Alerts

Google Alerts is a good way to keep track of topics and companies of interest. You get e-mail updates with news and blog entries that match any search term. For general search terms use ‘once a day’ and for companies use ‘as-it-happens’.

5. Social Networks

I joined Twitter over a month ago.  The 30 or so people I follow seem to have the same interests as I do. What’s more important is that they point me to topics and reference sites that I would not have discovered otherwise. I’ve dropped a few people that were overly verbose or had mostly inane (like  “I’m going to walk the dog now.”) tweets.

I’m also a member of LinkedIn. Besides connecting with people you know there are numerous groups you can join and track topical discussions. Unfortunately, there are quite a few recruiters on LinkedIn which somewhat diminishes the experience for me.

I don’t have a Facebook account because my kids told me you have to be under 30 to join. Is that true? 🙂

6. Books

I browse the computer section of the bookstore on a regular basis.  I even buy a technical book every now and then.

Downloading free Kindle e-books is another good source (and free, of course) e.g. here are a couple though Karl’s post: Foundations of Programming. There’s a lot of on-line technical reading material around. Having a variety on the Kindle allows me to read them whenever the mood strikes me.  One caution though: the Amazon conversion from PDF and HTML to e-book format is usually not very good. This is particularly true for images and code. But still, it’s free — you get what you pay for.

7. Magazines

There are numerous technical print publications around, but they are becoming rare because of the ease of on-line alternatives.  I used to get Dr. Dobbs journal but they no longer publish a print version, but it is still available electronically though.

I miss that great feeling of cracking open a fresh nerd magazine.  I still remember the pre-Internet days when I had stacks of BYTE laying around the house.

8. Webinars

These tend to be company sponsored, but the content about a product or service that you may not know a lot about is a good way to learn a new subject.  You just have to filter out the sales pitch. You typically get an e-mail invitation for these directly from a vendor.

9. Local User Groups

I’ve talked about this before (at the end of the post).  In addition to software SIGs, look into other groups as well. For me, IEEE has a number of interesting lectures in the area.

Face to face networking with like professionals is very important for career development (“It’s not what you know — it’s who you know” may be a cliche, but it’s true.).  Go and participate as much as possible.

If there’s not a user group in your area that covers your interests, then start your own! For example: Starting a User Group, Entry #1 (first entry of 4).

10. Conferences and Seminars

Press your employer for travel and expenses, and go when you can. This is another win-win for both of you.  Like Webinars, vendor sponsored one day or half day seminars can be valuable.  Also, as in #9, this is another opportunity to network.

Just getting out of the office every now and then is a good thing.

11. Podcasts

These may be good for some people, but I rarely listen to podcasts.  My experience is that the signal to noise ratio is very low (well below 1). You have to listen to nonsense for long periods of time before you get anything worthwhile. But that’s just me. Maybe I don’t listen to the right ones?

12. Discussion Sites

CodeProject and Stack Overflow are my favorites. Also, if you do a search at Google Groups you can find people talking about every conceivable subject.

Asking good questions and providing your expertise for answers is a great way to show your professionalism.

13. Blogging

IMO your single most important professional skill is writing. Having a blog that you consistently update with material that interests you is a great way to improve your writing skills.  It forces you to organize your thoughts and attempt to make them comprehensible (and interesting) to others.

14. Take a Class

If you have a University or College nearby, they probably have an Extension system that provide classes.  Also, there are free on-line courses available. e.g.: Stanford, MIT, and U. of Wash.

UPDATE (6/23/09): Here’s some more fuel for #13: The benefits of technical blogging. All good points.

CodeProject Note:  This is not a technical article but I decided to add the ‘CodeProject’ tag anyway. I thought the content might be of general interest to CPians even though there’s no code here.

Exploring Cloud Computing Development

Cloud ComputingIt’s not easy getting your arms around this one. The term Cloud Computing has become a catch-all for a number of related technologies that have been used in enterprise-class systems for many years (e.g. grid computing, SOA, virtualization, etc.).

One of the primary concerns of cloud computing in Healthcare IT is privacy and security.  A majority of the content and comments in just about every article or blog post about CC, re: health data or not, deal with these concerns. I’m going to save that discussion for a future post.

I’m also not going to dig into the multitude of business and technical trade-offs of  these “cloud” options versus more traditional SaaS and other hybrid server approaches.  People write books about this stuff and there’s a flood of Internet content that slice and dice these subjects to death.

My purpose here is to provide an overview of cloud computing from a developers point-of-view so we can begin to understand what it would take to implement custom software in the cloud.  All of the major technical aspects are well covered elsewhere and I’m not going to repeat them here. I’m just going to note the things that I think were important to take into consideration when looking at each option.

Here‘s a simplified definition of Cloud Computing that’s easy to understand and will get us started:

Cloud computing is using the internet to access someone else’s software running on someone else’s hardware in someone else’s data center while paying only for what you use.

As a consumer, for example of a social networking site or PHR lets say, this definition fits pretty well.  There’s even an EMR that is  implemented in the cloud, Practice Fusion, that would fit this definition.

As a developer though,  I want it to be my software running in the cloud so I can make use of someone else’s infrastructure in a cost effective manner.  There are currently three major CC options.  Cloud Options – Amazon, Google, & Microsoft gives a good overview of these.

The Amazon and Google diagrams below were derived from here.

Amazon Web Services

Amazon Cloud Services

The Amazon development model involves building Zen virtual machine images that are run in the cloud by EC2. That means you build your own Linux/Unix or Windows operating system image and upload it to be  run in EC2. AWS has many pre-configured images that you can start with and customize to your needs. There are web service APIs (via WSDL) for the additional support services like S3, SimpleDB, and SQS.  Because you are building self-contained OS images, you are responsible for your own development and deployment tools.

AWS is the most mature of the CC options.  Applications that require the processing of huge amounts of data can make effective you of the AWS on-demand EC2 instances which are managed by Hadoop.

If you have previous virtual machine experience (e.g. with  Microsoft Virtual PC 2007 or VirtualBox) one of the main differences working with EC2 images is that they do not provide persistent storage. The EC2 instances have anywhere from 160 GB to 1.7 TB of attached storage but it disappears as soon as the instance is shut down. If you want to save data you have to use S3, SimpleDB, or your own remote storage server.

It seems to me that having to manage OS images along with applications development could be burdensome.  On the other hand, having complete control over your operating environment gives you maximum flexibility.

A good example of using AWS is here: How We Built a Web Hosting Infrastructure on EC2.

Google AppEngine

Google App Engine

GAE allows you to run Python/Django web applications in the cloud.  Google provides a set of development tools for this purpose. i.e. You can develop your application within the GAE run-time environment on our local system and deploy it after it’s been debugged and working the way you want it.

Google provides entity-based SQL-like (GQL) back-end data storage on their scalable infrastructure (BigTable) that will support very large data sets. Integration with Google Accounts allows for simplified user authentication.

From the GAE web site:  “This is a preview release of Google App Engine. For now, applications are restricted to the free quota limits.”

Microsoft Windows Azure

Microsoft Windows Azure

Azure is essentially a Windows OS running in the cloud.  You are effectively uploading and running  your ASP.NET (IIS7) or .NET (3.5) application.  Microsoft provides tight integration of Azure development directly into Visual Studio 2008.

For enterprise Microsoft developers the .NET Services and SQL Data Services (SDS) will make Azure a very attractive option.  The Live Framework provides a resource model that includes access to the Microsoft Live Mesh services.

Bottom line for Azure: If you’re already a .NET programmer, Microsoft is creating a very comfortable path for you to migrate to their cloud.

Azure is now in CTP and is expected to be released later this year.

UPDATE (4/27/09) Here’s a good Azure article:  Patterns For High Availability, Scalability, And Computing Power With Windows Azure.

Getting Started

All three companies make it pretty easy to get software up and running in the cloud. The documentation is generally good, and each has a quick start tutorial to get you going. I tried out the Google App Engine tutorial and had Bob in the Clouds on their server in about 30 minutes.

Bob's Guest Book

Stop by and sign my cloud guest book!

Misc. Notes:

  • All three systems have Web portal tools for managing and monitoring uploaded applications.
  • The Dr. Dobbs article Computing in the Clouds has a more detailed look at AWS and GAE development.

Which is Best for You?

One of the first things that struck me about these options is how different they all are.  Because of this, from a developer’s point-of-view I think you’ll quickly have a gut feeling about which one best matches your current skill sets and project requirements. The development components are just one piece of the selection process puzzle though. Which one you actually might end up using (it could very well be none) will also be based on all your other technical and business needs.

UPDATE (6/23/09): Here’s a good high level cloud computing discussion: Reflections on Executive Briefing Event: Cloud & RIA.  I like the phrase “Cloud Computing is Elastic” because it captures most the appealing aspects of the technology.  It’s no wonder Amazon latched on to that one — EC2.

Selecting a MVC/MVP Implementation for a Winforms Project

I’m not a computer scientist. I’m also not one of the many über programmers that create and analyze software frameworks and techniques. I simply design and develop software that attempts to meet my customer’s needs. To that end I’m always looking for the best tools available to get the job done.

Jeremy Miller states the importance of design patterns well:

I know many people blow off design patterns as ivory tower twaddle and silly jargon, but I think they’re very important in regards to designing user interface code. Design patterns give us a common vocabulary that we can use in design discussions. A study of patterns opens up the accumulated wisdom of developers who have come before us.

My opinion: You don’t need to be a rocket scientist to understand design patterns. Most are just common sense. Complex patterns are designed to solve complex problems. Design patterns should be thought of as a tool that you use just like any other. Don’t let the ‘ivory tower twaddle’ scare you away.

I think most people would agree that one of the key components to creating a successful software product is quality. I’ve developed .NET applications in the past and have experienced the difficulty of testing and maintaining the functionality of Winform forms and components when they are created with the default Visual Studio tools. If you’re not careful, here’s what you end up with:


Photo hat tip: Josh Smith from Using MVC to Unit Test WPF Applications — a very good and relevant article.

I should note here that the development of software for medical devices already has rigorous verification and validation processes to ensure quality. See FDA Good Manufacturing Practice (GMP – Quality System Regulation) subpart C–Design Control (§ 820.30 sections f & g). However, these requirements do not preclude the need for development techniques that make the software more robust and maintainable. On the contrary, the higher the software quality, the easier it is to meet these standards.

I’ve recently spent some time trying to select a GUI architecture that will allow us to create a more robust unit testing environment. This is why I started looking at Model-View-Controller (MVC) and Model-View-Presenter (MVP) design patterns. The need for these types of design patterns is twofold:

  1. Separation of Concerns (SoC), which allows for
  2. Improved Testability.

There are many articles and blog posts that describe MVC, MVP, and their numerous variations. These techniques have been around for many years but the current corner-stone comes from these Martin Fowler articles:

Once you understand these concepts you can start to grasp the trade-offs of all of the available MVC/MVP flavors. If you’re like me, one of the problems you’ll run into is that there are so many different approaches (and opinions) that you’ll be left wondering which is best to implement. The only advice you’ll get is that it’s a matter of choice. Great, thanks! From the article above, Josh puts it best:

If you put ten software architects into a room and have them discuss what the Model-View-Controller pattern is, you will end up with twelve different opinions.

This is when you turn from the theory and start looking for concrete implementations that might be suitable for your situation. Microsoft has released an ASP.NET MVC Framework as part of VS2008, but all of the Winform code samples I found were part of either blog posts or articles.

As you look at the different implementations (and relevant snippets), you quickly realize that following these design patterns requires significantly more work than just adding your application’s logic directly to the IDE generated delegates. The additional work is expected and is the trade-off for improved testability.

That’s fine, and worth it, but it’s still time and money. We do not have the resources, or experience, to undertake a full Test-Driven Development (TDD) effort. We will implement MVC/MVP on only the displays that we feel are the most vulnerable.

I’m not going to list all of the candidate examples I looked at. I will mention that Jeremy’s series of articles (here) dig deep into these issues and have lots of good code examples. Each approach has their pros and cons, just like the one I’ll present here. We’ll try to use it, but may end up with something else in the end. As we become more experienced, I suspect we’ll evolve into a customized solution that best meets our needs.

A Promising Candidate:

Implementing the Passive View — a Derivative of the Model-View-Control by Matthew Cochran.

Passive View — a Derivative of the Model-View-Control

This hybrid approach appealed to me for a couple of reasons. The first is that I spent several years doing Swing development, which uses a MVC that also allows multiple simultaneous views of a single model. I also like the event driven approach, which is not only heavily used in Java, but is also well supported in .NET. In any case, the View is passive and all of the important functional logic is centralized in the Controller class which can be easily tested with real or mock Model and View objects.

Matthew has done a good job of providing support generic classes that make implementation somewhat less cumbersome. The MvcControlBase class provides generic Control-View wiring while ChangeRequestEvents manages all events in a single class.

The project download provided by the article is a VS2008 solution. We’re still using VS2005, but I was able to back-port the project to VS2005 with only minor modifications that had no effect on functionality. The VS2005 project is available for download here:

MVC-PV-2005.zip (23K)

Final Thoughts:

I see adoption of MVC/MCP methodology for GUI development as a critical component for improvement in software reliability, quality, and long-term maintainability. Also, structuring the application side with MVC/MVP is only half the battle. Developing an effective testing strategy must go along with it in order to achieve these objectives. Until Microsoft provides an integrated Winforms MVC solution like they did for ASP.NET, we’ll just have to continue to roll our own.

I’d like to hear about your experiences, suggestions, and recommendations on any of these topics.


UPDATE (6-May-08): Here’s a good MVC article by Jeff Atwood: Understanding Model-View-Controller

UPDATE (16-Jun-08): Another reference: Everything You Wanted To Know About MVC and MVP But Were Afraid To Ask

UPDATE (11-Sep-08): Still more: MVC vs. MVP: A Hillbilly’s Journey.



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