What to use? MVC, MVP or MVVM or…?
I will start a Java project to develop a desktop application. What to use as presentation layer pattern (MVC, MVP,MVVM or....)?
...if it is possible, with some working small example... :-)
Answer
Actually, the ultimate post you're looking for is this answer this answer from Karsten Lentzsch (of JGoodies fame) in the Swing Frameworks and Best Practices Swing Frameworks and Best Practices thread.
Hello,
I've been writing Swing apps for several years that many people find elegant. And I teach developers in working with Swing efficiently: how to structure and assemble applications, how to bind and validate date, as well as how to find, design, layout, and implement well-designed screens in Swing.
I'd say there are no "best practices" for Swing available online. And I doubt that anyone can provide "best" practices, because that would require discussions among Swing developers and solution providers about approaches, what works well technically and what is easy to understand, and work with. Also, best practices would explain who can achieve what result quality, and they would describe the production time and production costs; but I could never find these information online or in a Swing book.
In my opinion, the lack of good practices and information how to build a Swing app is the biggest obstacle developers face when starting with Swing. Most developers I worked with were slow in finding design, implementing layouts, building panels, binding data, handling events, and arranging the different code parts and code layers. And many Swing apps I've seen suck; besides their poor visual design they are difficult to understand and even small changes costs a lot. Typically developers had no clue where to put what code?, how to separate concerns?, how to tie things together?, how to work with Actions?, how to launch an app?, and how to store and restore UI state? Most developers lack guidelines to follow.
But I've found that the average developer can work well with Swing, if only taken by the hand - in about 3 to 10 days. Almost all of your questions can be answered or addressed by code, libraries, the application architecture, patterns, general programming practices, well-designed examples, tutorials, etc. I teach a Swing development process that is built around a 3-tier architecture that seperates the domain, tool and presentation layers and that is based on a productive layout system. Even though most parts are done programmatically developers get results quickly and both the code and visual design becomes quite consistent. This can boost a developer's productivity a lot - to the extent that the Swing work takes a significantly smaller fraction of the project work.
So what can you do? I strongly recommend to study Martin Fowler's draft for further "Patterns of Enterprise Application Architecture". I've found that these patterns work really well with Swing and Swing teams - even for developers that are new to Swing and the Swing architecture. I'd pick the following patterns first: "Presentation Model", "Separated Domain", and "Separated Presentation". I personally favor the Presentation Model (Application Model for Smalltalkers), over the Model-View-Presenter pattern (MVP). However, MVP is a true and well studied alternative.
Fowler's patterns can be combined with a 3-client-tier architecture that scales well for moderately large Swing applications. It consists of a domain layer, a presentation layer, and a mediating model layer. I've outlined this architecture in my data binding presentation. MVP-based apps can be structured in these 3 client tiers too.
A key task for Swing applications is the data binding: how to connect domain objects and domain object properties to the Swing components. Basically you can copy your data back and forth, or build chains of adapters from your domain objects to the UI components. The copying approach is easy to understand and often the first choice for those who are new to Swing or data binding; I'd say this is a good choice. On the other hand, copying makes it much harder to synchronize views. Adapter chains and automatic or semi-automatic updates can significantly reduce the amount of code necessary to bind domain data to the UI. The downside is, that this approach is much harder to understand. As you've pointed out, Swing provides no great abstraction for a reusable and flexible model that can be used to bind text fields; the Document interface isn't appropriate for generic data access. There are a few libraries available that provide a ValueModel interface that is just intended to add a generic, powerful, and flexible model for single-valued data: Strings, booleans, numbers, dates, etc.
I'm not aware of a Swing book that explains a true Swing application development process. Ideally such a book would combine the patterns, architecture, and data binding techniques mentioned above and would describe how to implement it in Swing. Anyway, there's a 10-years old documentation for a Smalltalk application development process that does just that. Oracle's JClient architecture and documentation is not that complete but may be easier to read for Java developers. I provide a presentation about data binding that is about the Fowler patterns, a 3-tier architecture and a Swing implementation for these patterns and an automatic data binding. The tutorial sources of my Binding library may help you get aquainted with adapter chains and the ValueModel interface. The best documentation for the MVP pattern can be found in the Dolphin Smalltalk docs.
Once you've choosen your architecture and desktop pattern set, you should address the following more basic Swing tasks: 1) improve the appearance by choosing a set of professional look&feels appropriate for your target platform set, 2) choose a layout system that helps you build well designed and consistent screens quickly, 3) choose a data validation solution, and 4) grab a bag of solutions for everyday Swing tasks.
There are a couple of projects that outline a Swing architecture, address the data binding and typical Swing tasks, for example: Sun's JDNC, Oracle's JClient/ADF, the Spring RCP, the NetBeans platform. I provide a commercial suite of Swing solutions that is based on the open source JGoodies libraries and adds a bag of solutions and sources for all public JGoodies tools and demos. These sources are intended to explain how to tie together all issues mentioned above.
Let me add my standard warning about so called "MVC" frameworks. Swing doesn't use MVC, it uses a modified pattern. MVC is frequently misquoted and misunderstood - especially in the context of Swing. Also, MVC is good for UI components, not for applications. Hence I recommend to look for concepts, solutions, and libraries that reflect and work with the Swing architecture, not MVC.
The inventor community of the MVC pattern introduced the ApplicationModel (now known as Presentation Model) around 1993; MVP followed a bit later. In my opinion these two patterns are much more useful for Swing than MVC. Recently the environment that brought the Presentation Model pattern to a larger audience moved on to a new architecture: "Pollock". Interested readers may google to see how that differs from the adapter chains that are often combined with Presentation Models.
Last but not least a personal statement. I can work much better with Swing than with other toolkits or frameworks I used before; I can do more with less code, the code is better structured, it's easier to maintain, and I get results quickly.
Hope this helps. Best regards, Karsten Lentzsch
References: Fowler's further patterns - http://martinfowler.com/eaaDev Data binding presentation - http://www.jgoodies.com/articles/ Smalltalk app dev process - http://www.cincom.com/downloads/pdf/AppDevGuide.pdf MVP pattern documentation - http://www.object-arts.com/EducationCentre/Patterns/MVP.htm Sun's JDNC project home - http://jdnc.dev.java.net/ Oracle's ADF FAQ - http://www.oracle.com/technology/products/jdev/htdocs/905/adffaq_otn.html Spring RCP project home - http://www.springframework.org/spring-rcp.html NetBeans platform home - http://www.netbeans.org/products/platform/ JGoodies Swing Suite - http://www.jgoodies.com/products/index.html
If you don't know Karsten and JGoodies, then believe me, this guy really knows what he's talking about. I warmly recommend to read carefully his answer and the material he posted as reference. More specifically, be sure to check his Desktop Patterns and Data Binding presentation. Surprisingly, I prefer the old version to the new one.
Let me quote his slide about MVC vs MVP:
- Yes, Swing uses an extended form of MVC internally
- But MVC is for components, MVP is for applications
And then from the Summary:
- Separate the domain from the presentation!
That is Separated Presentation. - Separate Autonomous View if appropriate
- Choose MVP or Presentation Model
- Swing makes Presentation Model easy
- PM requires a binding solution
But I can't do a better job than Karsten at explaining this, I can at best paraphrase him. So just read him!
Also maybe have a look at Desktop Java demos for learning (more precisely Scott Violet's answer).