VB WPF MVC (Model + View + ?)

Question

Hi,
I have an old VB6 application. I want to recreate it in VB.Net using WPF. But I am a bit confused about the "Model View Controller"-pattern. I have two books about design patterns (GoF and J.Bishop) afair this pattern is indeed not mentioned inside one of the two books. I have also searched the internet I found some java-examples. But I have still no clue how I should use MVC-Pattern (should I?) in my new WPF-application.
Let's say for example my model (in fact it is more complex) is only a wheel rim (circle) with the properties Manufacturer, Diameter and Depth. The user should be able to modify the properties using textboxes and ComboBoxes.
Could somebody create a small example that explaines the MVC-Pattern with WPF? Of course I like reusable classes to have a feasible concept throughout the whole application.
thanks in advance Oops

Answer 1

Bevcause of the rich binding support available, WPF (and Silverlight) are well suited to MVVM (Model-View-ViewModel). MVVM is an extension of MVC that uses a view model to bind the current state of a view, instead of manipulating the view directly.

There are a bunch of MVVM frameworks available, as well as Microsoft's own Prism framework (which is arguably more useful if you have a larger, modular application).

Answer 2

WPF is probably more well suited to MVVM (Model-View-ViewModel). I'd recommend reading this MSDN article on MVVM and, perhaps, following their advice. There's also a nice collection of links I found on the Bryant Likes blog.

Answer 3

Here's a "brief" description of what the MVC pattern is and how I would apply it to a WPF application.

(I might have a few details slightly off since I've mainy hacked in Silverlight but the concept is similar enough.)

Basically, the idea is to separate concerns and define interfaces between the different parts of an application, with the goal of keeping the code structured and maintainable.

The Model in your example would be pretty much exactly as you described the wheel rim - a WheelRim class with the various properties defined in suitable data types. I would put the model i an separate assembly to keep it apart from the other code, but you can settle for just keeping the model classes in a "Models" folder. The model would also have a "twin" in a database, the model classes being pretty much one-to-one-mapped to tables.

(You might wanna have a look at Linq2SQL or Entity Framework, if the database is defined you can pretty much get the model for free along with suitable database access code.)

The View would be the actual WPF xaml files - Defining the Grid or Canvas or what have you. On the WheelRimView there would be labels and textboxes for displaying or accessing the different properties, perhaps along with product images and the like. The code behind for the view would have all the relevant event handlers (start, button_click and so on) for getting the data from the fields and passing them to the controllers.

The Controller would be any "handler code" that you would use to manipulate the data. We're talking the basic CRUD operations here, along with validation and the like. Also, the controller layer would be responsible for compiling the data in a format that can go seamlessly into the View. The WheelRimController hence would have methods like "GetWheelRimList", "GetWheelRim", "AddWheelRim", "ModifyWheelRim" and "DeleteWheelRim". The methods take the values as in parameters and manipulate the model objects accordingliy. the

I would recommend keeping the code-behind of the xaml files free from any "controller"-ish code like validation, aggregation and the like - the code behind should basically only take the values from the textboxes, listboxes and such and send them on "as is" to the controller methods for processing. Also, you should keep any data formatting code to a minimum when getting data for presentation (i.e., no filtering or translating in the view).

A typical use case of "User opens a wheel rim and edits the diameter" would play out thus in code:

1. User clicks "Edit" on a list page. The WheelRimView page loads.
2. The WheelRimView.Load() method (or corresponding) calls WheelRimController.GetWheelRim(wheelRimId).
3. WheelRimController.GetWheelRim(wheelRimId) gets the corresonding data from a database table and populates the properties of a WheelRim object, which is returned to the WheelRimView.
4. The WheelRimView inserts the property values into the labels and textboxes.
5. The user changes the diameter value and clicks the "Save button.
6. The WheelRimView.Save() method calls the WheelRimController.ModifyWheelRimDiameter(wheelRimId, diameter) method.
7. The WheelRimController.ModifyWheelRimDiameter(wheelRimId, diameter) method parses the diameter (if it is a string) and loads the model object. It applies the modified value to the model object and saves it into the database.
8. The WheelRimController.ModifyWheelRimDiameter(wheelRimId, diameter) returns a status code to the WheelRimView (for instance a predefined numeric stating any validation errors) to report the success of the save.
9. The WheelRimView displays a result message (hopfully "saved") to the user.

I hope that clears a few bits up.