I have read many articles on the MVP pattern. Some folks say it is too complex and some say it's outdated. However to me it would seem like the perfect way to provide unit testing access to the UI - which is what I'm aiming to achieve.
Have you used MVP and if so what do you think?
Model View Presenter, Model View Controller, traditional three tier (UI/Business Logic/Data Storage) or virtually any other architecture that isolates the various concerns of your code help you write tests.
Often the architecture is somewhat dictated by your tool: the Asp.Net MVP tags seem to indicate that you have already made your choice there. The trickiest part to test in any configuration is the UI, because even if you create a mock UI that performs all the functions the user can... at some point you will have to render it in a browser and assure yourself that the theory is sound.
Note that this does not discount the benefits of a mock presenter UI with unit tests that exercise all the options the user will have: doing so puts you light years ahead of someone doing straight UI testing alone. On the other hand, I have yet to find a program where the UI always rendered as we expected in every browser. Finding these cases still requires human intervention (or at best something like Selenium or Test Complete once you have the initial run-throughs).
Regarding the "obsolete" aspect, I think that is a red herring. There are of course religious wars regarding architectural choices, but the reason that MVP is being used in some ASP.NET projects is that there are quite a few who felt the traditional ASP.NET stack was too tightly integrated between the UI and the Business Logic. (I'm one of them.) For small projects that tight coupling isn't that big of a deal, and contributes to the quick "bring it up and running" ability of the form designer with databinding. In large projects, the limitations of these tools show up in a hurry, and having a "middle" tier hacked back in after the fact is a challenge: one you don't have to face with MVP.
I did an ASP.NET project using MVP last year. Yes, I was able to cover more with unit testing than I could before in the webforms world, but it felt hacky. Also, try explaining what you are doing to someone else. For some reason, people have a hard time grokking it. If I had to do it over again, I'd go with the ASP.NET MVC framework, since it is officially supported with tons of documentation and buzz, and not just a hack.
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I am starting a new project and was going to use it learn asp.net mvc.
But time is short and I won't have time to meet the requirements, learn mvc and end up with a well designed system. So I need to start with asp.net v4 and EF.
What sort of things should I do to allow an easy transition to MVC later?
I'd say the most important thing is the separation between business logic and presentation logic.
If you have a lot of business logic embedded on the aspx or on the code behind pages the transition will be harder.
Another thing that could complicate the transition is how intensively you use asp net web controls. If you can use independent UI controls from server side language (not everywhere of course, but as much as possible), things will be easier to migrate.
If you don't have time to meet the requirements, then you didn't give yourself enough time. If you are limited by time it's presumably because you are working for someone else, and you're constrained by their timetable and/or budget, so you need to build on what you know.
You should never blindly implement on a framework you don't know. You need to build time for prototyping, learn on your own, or pull in talent that already knows. If you are using a new framework and there is uncertainty, you should have enough time that you can cut after a certain point and rebuild in a way you do know you can do it.
You should also build on the best framework for the job -- there is no one-size-fits-all solution for any problem. What framework you choose should be based on the user requirements, technical/business limitations, projected growth and life (maintenance needs), and your available resources. Choosing is based on your personal past experience, and prototyping. If you don't have the experience and don't have time to prototype in at least a couple frameworks, you are in a bad spot right from the start.
That all said, I personally think ending up with a "well designed" system in WebForms is INCREDIBLY difficult, especially compared to doing it within MVC, and that in the ASP.NET space MVC is a much better framework in almost all situations than WebForms. I am biased and will outright say I think Webforms is fundamentally flawed in its philosophy; most of the code works as small examples but falls apart and becomes unmaintable as you grow, and even the example code from MS suffers this issue. But you should not use some random person on the internet's opinion as the basis for your design choices. I am just pointing this out because I want to be clear that I am not endorsing specifically WebForms, I am endorsing "use what you know" -- whether you "know" it from previously using or take time to learn it.
Does data binding fit in a 3 layered architecture? Is dropping a grid-view on a web form and binding it to a LinkDataSource or SQLDataSource considered bad? The way I see it, that's the Presentation Layer talking to the Data Access Layer. I once heard a "professional developer" say never ever do this, so what's the alternative if you shouldn't?
The way you are doing is ok if it is a small project, but if you want your app. to have flexibility to support Windows/ Web in future then you must use Layers.
Please follow this link http://www.dotnetspider.com/resources/1566-n-Tier-Architecture-Asp.aspx
You should have a middle tier between Presentation and Data Access layers, the middle tier is pulled out from the presentation tier and, as its own layer, it controls an application’s functionality by performing detailed processing.
The main task of Business layer is business validation and business workflow.
When you build your business logic components into an SDK, you are effectively disconnecting it from your Web application, and any input validation that it performs. Therefore, your business logic components are the last line of defense to make sure that only valid values make it into your database.
Databinding is, of course, necessary to effectively dispay data.
Tooling is great and can boost productivity. It is equally important to understand what the tooling is generating, even at a basic level, in order to be able to effectively utilize the generated code.
The reaction you describe seems a bit extreme. If a wizard can generate some code that works for ya, then use it. If you don't understand the generated code then that is the next priority; learn about what it is doing and why. In the meantime, you have a page that people can put eyes on regardless of how it got there.
I am a bit pragmatic when it comes to tools. You do what you have to do. But, if after [insert appropriate internship length] you are still using code gen and cannot customize or fix it then you (as in the royal you, not the you you) are being lazy or stupid or both. ;-)
OT:(almost) Never say never unless you want to lessen the impact of what you are trying to communicate.
my 2 pesos.
When you're doing a small project or a prototype, go with the LINQDataSource or SQLDataSource. However, the downsides of those data sources are serious enough for you to think hard if they are appropriate. If your doing a multi-layered or multi-tear architecture, they simply don't fit. But even if your architecture isn't that strict, you should ask yourself how big this application is going to be and how likely it is going to be that you will make changes to the system in the future. How much time it is going to take you when you want to make a change to the database?
I've seen projects were the developers used those data sources, because those were the constructs that were used in those nice ASP.NET video's. However, when the projects grown from prototypes to big production applications (yes, I’ve seen it happen, the prototype seemed good enough), the lack of compile time support (your queries are defined in markup!) made it very hard to do any change to the system.
When you need to make a change to the system, that will be the time that you’ll see that the cost of the change is a magnitude bigger than the time you saved by flattering your architecture.
When I first heard about ASP.NET MVC, I was thinking that would mean applications with three parts: model, view, and controller.
Then I read NerdDinner and learned the ways of repositories and view-models. Next, I read this tutorial and soon became sold on the virtues of a service layer. Finally, I read the Fluent Validation documentation, and I'll be darned if I didn't end up writing a bunch of validators.
Tonight, I took a step back and thought about what had become of my project. It seems to have become the victim of the design pattern equivalent of "feature creep". Somehow I'd gone from Model-View-Controller to Model-Repository-Service-Validator-View-ViewModel-Controller. You want loosely coupled and DRY? We got your loosely coupled and DRY right here! But I'm wondering if this could be a case of too much of a good thing.
Am I right to be concerned? Or is this actually not as crazy as it sounds? On one hand, it seems crazy to have so many layers. On the other hand, every layer has a clearly defined purpose that makes sense to me. Have your MVC applications turned into MRSVVVMC apps too? If not, what do they look like? Where's that right balance?
If you have one form with three attributes, this is overkill.
But if you have a 'real' application, and the responsibilities of each layer are well defined, I'd consider it pretty reasonable.
It sounds to me like you found a pattern and went looking for a problem. You should find a problem, and use the appropriate tool from your toolbox... not all the tools. Unless this is an academic exercise of course.
We are currently designing a business application that has two primary requirements for it's UI:
1) run on the Desktop (WPF) for enterprise users to provide a rich user interface, interoperate with other applications, access the filesystem, work offline, work with special local hardware, etc.
2) run on ASP.NET/Ajax to provide several components of this application to customers (internet). Unfortunately Silverlight is not (yet) an option.
Even though we don't have to make the full application available on the web, some of these components are fairly complex and we would like to share as much UI code as possible with the WPF implementation.
What options do we have to reach this goal? Is there a pattern that works well with both technologies?
Update:
Thanks for the answers even though they don't include the one I was looking for! :)
I don't think UI generators are a good option. Like Eduardo pointed out you will probably end up with problems in both worlds. I will check out Sculpture though.
I've been thinking along these lines for a while now, and I've yet to come up with a great answer. That being said, here are some of my thoughts:
If you used some variation of the various MVP/MVC/MVVM UI methodologies and you were very disciplined in this approach (i.e. not mixing presentation stuff with behavior stuff), you'd probably be farther down the road.
You might consider investigating the various DSL toolkits that have cropped up, the idea being to create a simple "language" to describe your UI at a high level and generate a representation of that UI in WPF/ASPX.
Also, I ran across this recently. I have no idea how good it is. I'm planning to take a closer look when I get the chance.
Good luck!
The unfortunate truth is that Asp.net/ajax (the web in general for that matter) and WPF (and heck, let's throw WinForms in there for good measure) have very different User Interface models and what works well for one is not necessarily going to work well for another. That's not to say that you can't share logic between applications written for either technology, but, I'll make a stretch here, your UI logic is not going to be in that category.
I've been using a variation of MVVM for WPF and ASP.Net MVC most recently and I'd say they are very good fits for the technology at hand. However, while they are very similar, they have their differences and I'm not sure you could write an abstraction layer (in any decent amount of time) that could take advantage of the great features in both technologies.
Ultimately, I'd say that your best bet is to follow some SOA patterns and extract as much of your business and data access logic into common libraries as possible. Then, write separate user interfaces in WPF and Asp.net to take advantage of those common libraries. This is the approach that my company is taking at the moment, and it's working like a charm.
It may seem daunting to write your UI logic twice (once for asp.net and once for wpf), but I think it's worth it so that your code can fit the patterns and practices that best fit those technologies.
As an aside, even though Silverlight is not an option, have you considered XBAP?
If a former job we did something similar. As Daniel Pratt says, we describe our interfaces in XML and then a render will create the form, report or whatever we decided to create.
We have to provide a Javascript function to do some UI validations in the HTML render, and a call to a java function in the Swing render.
Beware that you may end with imperfect apps in both worlds.
I am just starting a new ASP.NET project and using the MVP pattern. I did consider the MS MVC but it is not released yet and would be a big learning curve for some people on the team, so I opted for MVP now and possibly future projects MVC.
Anyway, it seems I will have a single Controller/Presenter class for every webform I have it the project. This is a lot of extra classes, essentially doubling the number of files in the web project. Is this how other people structure MVP or what are the alternatives?
This seems to be a common misconception -> "More files/classes == more complex"
The reason we chose to follow a UI separation pattern is to help separate concerns, make code easier and cheaper to change and maintain and (big, important and) we can unit test the complex parts and still keep the UI layer slim.
I'm going with the beta ASP MVC. The reason being, that while it is still only a beta (PDC very soon, that may have an impact on release and we've had 5 preview releases) it has a better framework to support this style than I could write in a reasonable time frame.
You could of course go with another framework, like castle monorail.
I think a lot of it depends but in most cases that is really the way it ends up going.
I personally use a n-tier architecture with data, business, presentation code. (Who knows what actual format I follow). I do get a lot more files than if I did everything in the aspx, but the code is much easier to manage.
To your question - I have seen many different takes on MVP and seen nothing that reduces the number of files, and I can't think of a way to reduce the number of files.
In my experience, I have reused view interfaces and even code behinds where the view structure is identical, but presenting different data. And you could also think of reusing the controllers where applicable.
I think it is worthwhile to note that having more files will be a natural consequence of moving to a more agile and test-drive development and developers will find it more and more natural as they go. (Just like some of us find it very natural having lots of methods inside a single file...)