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
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:
User clicks "Edit" on a list page. The WheelRimView page loads.
The WheelRimView.Load() method (or corresponding) calls WheelRimController.GetWheelRim(wheelRimId).
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.
The WheelRimView inserts the property values into the labels and textboxes.
The user changes the diameter value and clicks the "Save button.
The WheelRimView.Save() method calls the WheelRimController.ModifyWheelRimDiameter(wheelRimId, diameter) method.
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.
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.
The WheelRimView displays a result message (hopfully "saved") to the user.
I hope that clears a few bits up.
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).
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.
Related
I would like to know how you are Design your Qooxdoo Code.
I don't get the right Architecture which I am satisfied with.
It is hard to encapsulate the View with logic like services.
I hope someone can give me a hint to a Pattern or something to find a good solution.
One of Qooxdoo's greatest features is a strong OO class system, so really the pattern that you use is up to you - MVC, MVVC, etc are all possible because Qooxdoo's OO system provides you the tools to implement your preferred pattern(s).
One pattern that I find very useful, especially in creating larger apps, is to define custom widgets for editing models; for example, if you have models (aka "Business Objects" etc) for Customer, Invoice, InvoiceLine, and Address having a widget for CustomerEditor, InvoiceEditor, InvoiceLineEditor, etc is really useful firstly because it encapsulates the code, but also because it supports binding.
Binding is a very powerful feature of Qooxdoo - to see why, let's assume for a moment that each one of your Editor widgets has a property called value which is the thing being edited.
In simple binding, your editor can bind properties of the model to the widgets which display and edit those properties, eg CustomerEditor bind value.firstName and value.lastName to a couple of qx.ui.form.TextField and automatically changes to the customer's firstName or lastName will be updated in the two TextField's. Binding can work the other way around too, so that changes to the TextField are copied back into the model.
There is a controller class called qx.data.controller.Form that can simplify making this happen, and optionally incorporate validation of user values and user feedback too.
If you have separate Editor widgets, you can also bind to them - for example, Customer could bind value.address to an instance of AddressEditor, and InvoiceEditor could bind the currently selected InvoiceLine to InvoiceLineEditor etc
In a MVC application that lives on the web, it's easy to draw the line between view and controller - views display data to the user, while controllers gather input and route the user to views based on the input provided. But in a stateful (e.g. desktop) application, it's a bit harder to know where to draw the line, because the boundaries between operations are not as clear-cut as with a web application. So where do I draw the line?
For instance, I have a view in my application that lets the user place items on a grid. Right now I have the "place item on grid" code within the view itself (accessing the grid model to do the actual placement). But I could also put it in a controller, and pass the necessary information from the view to the controller. Neither seems like a clear-cut choice - putting the code in the view will eventually bloat the view, since there will be a large number of operations that the user can do, not just place items; but putting it in a controller just seems like an extra level of indirection, making the code harder to follow.
Or am I going about this all wrong? This is a WinForms app; my "view" is actually a form, and forms by their nature can both receive input and display information. So is the distinction meaningless? Or should I have the view be separate from the form? Or is the MVC pattern incompatible with WinForms altogether?
MVC is a separation of concerns. It is designed to help the programmer keep details of the two areas separate. The MODEL and VIEW are collections/groupings of objects.
Each object within the VIEW may be part of the class sets BUTTON, WINDOW, TEXTAREA etc.
Each object within the MODEL will have a type corresponding to your domain such as CUSTOMER_DETAILS, ADDRESS, POSTCODE etc
The CONTROLLER object provides an interface into your MODEL objects, which your VIEW objects will use to communicate to your system. The CONTROLLER may also contain functionality that can not possibly be stored in your MODEL objects.
Traditional MVC also allows the VIEW objects to bypass the CONTROLLER and talk directly to MODEL objects, but is not recommended.
All objects conform to OO principles, and are complete and fully functional objects.
This will probably be obvious but I can't find the best way.
I want to show the user's ToDo's in a listbox. These ToDo's are in the database and consist of an Id, UserId and Description.
The user logged in to the app.
How can I retrieve the ToDo's for that certain userId and set it up for binding to the listbox?
I was trying with an ObjectDataProvider but I cant figure out how to use that in combination with nonstatic stuff (like my _dbService, userId, language, ...).
Are the only options to make all those things static versus binding in the code behind?
If so, this means that ObjectDataProvider isn't very useful, no?
I find a lot of examples of it being used with a hardcoded parameter but I hardly see any situation where I'd need such a functionality..
I do all my WPF using the Model-View-ViewModel pattern. I've given you one link there but Google will give you loads. MVVM seems to be the standard pattern for WPF. This project is probably more complicated than you need but it is well-written and brings home the use of MVVM.
Basically, you create a Model of your data. In this case, you'd probably create a simple class (I'll call it ToDoItem) with properties Id, UserID and Description. Use your preferred mechanism to get a collection of these from the database. Link to SQL, Entity Framework, a standard query, whatever.
Then you have your ViewModel - you have an instance of the ViewModel for each instance of the Model: the VM has a reference to the M and 'forwards' properties to it. The ViewModel is what you use to manipulate the model.
Then you have your View - this is the UI. You set the DataContext of the View to be the ViewModel and then your bindings automatically bind to the ViewModel. Your View just ends up being the things you can see. All of the work gets done in the ViewModel. This means it's very easy to test.
So, when you click on a button in your View, the bindings pass this onto a Command in your ViewModel which manipulates the Model.
The UI is also a View with a ViewModel. So, your UI VM might load a collection of Models from the database and stick them in an ObservableCollection. The ListBox items collection would be bound to this ObservableCollection.
It's hard to explain all of this in a post like this. Read a couple of articles and see what you think. I'm still quite new at this, too, but I believe my reading about MVVM has paid off.
Hela Thomas, Tom here from Orbit One :)
MVVM is the way to go. I'm on my 4th project and WPF really shines if you use mvvm. You already tried MVC (or MVP as we did on recy*tyre) and that's a nice separation of concern.
MVVM takes it a step further since the viewmodel knows absolutely nothing about the view.
The view binds to the viewmodel, so it has a reference to it (2 way, super powerful and works beyond the typical MS demo). The viewmodel is just a poco and is a representation of your view, data + behaviour. Once you dig this paragraph the cool term mvvm will have no secrets.
I see if I can come up with a small demo. Maybe I'll have time later.
What I will come up with is a view (xaml, file 1) that binds to a viewmodel (file 2, a poco class, not to be mistaken with code behind). The model can be whatever you like (service layer or directly to the repositories). Using the power of 2 way binding we will bind to an observable collection meaning that if we add/delete/... something to the collection the view will pick it up without us putting energy into it.
My first 2 wpf projects was done with Caliburn Micro (see codeplex) which is a powerful framework based on conventions. It shields you away from hardcore wpf (creating tour dependency properties yourself mainly) and you can create something relatively fast without fully understanding wpf. That's a downside of itself but it worked for me. As of project 3 I started taming those dependency properties myself and it will make you a better wpf developer.
I see the question is from October.. did you find a good solution?
Say I have a WinForm CRUD(like) application. I want to follow best practices on this so I try and make it follow OOP and a n-Tiered design.
Unfortunately I am familar with the words but not the practice of them. So lets go with the following example: My CaseNote program. I have a tabbed application where you go to the search tab to find a member and then one of the options is to go to the CaseNote tab to create a new case note, look at existing CaseNotes, or create a follow up CaseNote to a Parent Note. All of this is for the member you selected from the search tab.
So if I am creating objects and passing them around to be used by different forms where should I be instantiating them? I had thought I would have 3 layers; UI, Object, DAL. Where I fall flat is where I instance tho objects. I can't instance them in the object layer, can I? Also, if I instance them on the form how do I pass them from form to form in a quite large app?
CaseNotes Screen Shot
If you want to look at some more words around this problem you want to look at MVP and MVC. (These stand for Model View Controller and Model View Presenter). Some people will shoot me down for saying this but they are quite similar in concept.
The aim of MVP and MVC is to allow you to design your application logic without even having to think about your application apperance. It also allows you to define your user interactions without implementing an actual GUI. Esentially your model is your application logic, your data, your classes which actually do stuff like talk to your database. Your presenter or controller is what interacts with your model and what controls your user interface and reacts to user operations on the interface. Finally your View is your winforms design or your web page.
I'm sure you will be able to find plenty of material on the web about this but to give you some concrete help with this problem should serve to inform and illustrate your reading.
The first thing you need to do is start creating your objects that represent your data. So you will have a CaseNote object which is contains the casenote data. You will have a case note data container of some sort such as a case note database. You can define the logical operations and properties of these as if they where real items.
Then you would move on to define your presenter or controller which will define the operations that you want to support from the GUI. At the same time you should define an Interface that will define for the presenter/controller what operations is can perform on the GUI. So for instance your presenter may expose a method called SearchForCaseNote which takes a string parameter. Your view Interface will expose a method called DisplayCaseNote. When a user clicks on the search button the view will pass through the command to the presenter which will then call the model to get the data. The presenter may format the data at this point, i.e. convert DateTime object to a string and then pass the data back to the view through the interface define method called DisplayCaseNote.
You don't have to use the View interface, you could call into the view directly, but having the interface means you can have many different view implementations.
One last thing i need to mention is where you create these different parts of your application. My view is everything thing should fall out from the presenter/controller. So when you application starts it creates the presenter/controller object which then create and displays your view passing itself as a variable to the view. The presenter/controller can then either create the initial models by loading them from disk or ideally discover them through a dependency injection container like unity. In fact using unity to discover the view implementation is probably a better idea again as it gives you true seperation between view and presenter/controller. When you come to move to another view, (i.e. open another window), your presenter/controller should expose a method such as DisplayDetailPage which the view calls when a button is clicked. This would create the presenter/controller for the next view which would in turn create the view and get a reference to the model.
Hope this helps.
I think you should use the RocketFramework
I am developing a windows forms application. It was basically evovled with a mix of BDUP and prototyping.
I have about 1500 lines of code (excluding IDE generated partial class... 1465 to be exact) in the form and the form has 6 tabs (9 subtabs). Does not have more than 10 controls in each form so multiple form solution would be an overkill.
I have a set of entity classes that when serialized give me an XML representation that I store in an XML file. I've encapsulated this with a Repository pattern so I could move the storage to a database in future. The form uses the entity classes (for save/edit) and the Repo factory (add, retrieve and save).
Now, my problem is that much of the 1500 lines of code deals with interaction between UI elements (making a choice in a Combo disables some elements, or displays different items in a grid, handle tab transitions (next/back buttons), loading menus (each distinct item in the xml file repository becomes a menu item), new/edit mode etc (I've three distinct sets of new/edit on the same form).
What would be best approach here to move the element interaction out? Let's say, I may decide to make it web-based UI in future.
More importantly what are the composite refactorings I can apply?
What patterns I should refactor to / towards?
Thanks for helping out.
Note: I'm reading Refactoring to Patterns... Specifically I wanted to have a "howto"/tips on Refactoring to MVC...
Martin Fowler describes different UI architectural patterns in this article. It's fairly long, but well worth reading. You will then be able to determine which patterns and architectural models fit your scenario the best.
At the end of the "Model View Controller" section of that article, Fowler mentions these items, which seem applicable for you:
Make a strong separation between presentation (view & controller) and domain (model) - Separated Presentation.
Divide GUI widgets into a controller (for reacting to user stimulus) and view (for displaying the state of the model). Controller and view should (mostly) not communicate directly but through the model.
Have views (and controllers) observe the model to allow multiple widgets to update without needed to communicate directly - Observer Synchronization.
See the article and its links for more information. Good luck!
You should look into the Model-View-Controller (MVC) design pattern to abstract your business logic from your display logic.
There is also another flavor of the same thing called the Model View Presenter.
Both of these are extensively documented on the net.
Regards,
Joon