Is MVVM pointless? [closed]

Answer 1

As the pattern itself MVVM is great. But WPF's control library shipped with NET 4.0 data binding support is very limited, it is a lot better than WinForm, but still it's not enough for bindable MVVM, I would say it's power is about 30% of what is needed for bindable MVVM.
Bindable MVVM : it's UI where ViewModel is wired with View only using data binding.
MVVM pattern is about the object representation of the ViewState, it doesn't describe how you maintain the sync between View and ViewModel, in WPF it's data binding but it can be anything. And actually you can use MVVM pattern in any UI toolkit which support's events\callbacks, you can use it in pure WinAPI in WinForms (I did, and it's not much more work with events\callbacks), and you can even use it in Text Console, like rewrite DoS's Norton Commander using MVVM pattern.

In short: MVVM is not pointless, it's great. NET 4.0 WPF's control library is trash.

Here is the simple proof of concept ViewModel which you can't data bind in pure MVVM manner using WPF.

public class PersonsViewModel
{
    public IList<Person> PersonList;
    public IList<ColumnDescription> TableColumns;
    public IList<Person> SelectedPersons;
    public Person ActivePerson;
    public ColumnDescription SortedColumn;
}

You can't data bind WPF's DataGrid column headers, you can't data bind selected rows, etc etc, you will either do it in code simple way, or write a 200 lines of XAML hack code for these 5 lines of simplest ViewModel. You can only imagine how things get worser with complex ViewModels.
So the answer is simmple unless you are writing Hello World application, using bindable MVVM in WPF is pointless. You will spent most of your time thinking on hack to bind you ViewModel. Data binding is nice but be ready to fallback to event's 70% of time.

Answer 2

I deal with the dialogs issue by cheating. My MainWindow implements an IWindowServices interface that exposes all of the application-specific dialogs. My other ViewModels can then import the services interface (I use MEF, but you could easily just pass the interface through constructors manually) and use it to accomplish what is necessary. For instance, here is what the interface looks like for a little utility application of mine:

//Wrapper interface for dialog functionality to allow for mocking during tests
public interface IWindowServices
{
    bool ExecuteNewProject(NewProjectViewModel model);

    bool ExecuteImportSymbols(ImportSymbolsViewModel model);

    bool ExecuteOpenDialog(OpenFileDialog dialog);

    bool ExecuteSaveDialog(SaveFileDialog dialog);

    bool ExecuteWarningConfirmation(string text, string caption);

    void ExitApplication();
}

This puts all of the Dialog executions in one place and it can be easily stubbed out for unit testing. I follow the pattern that the client of the dialog has to create the appropriate ViewModel, which they can then configure as needed. The Execute call blocks and afterward the client can look at the contents of the ViewModel to see the Dialog results.

A more 'pure' MVVM design may be important for a large application, where you need cleaner insulation and more complex composition, but for small to medium sized apps, I think a practical approach, with appropriate services to expose required hooks, is quite sufficient.

Answer 3

Design patterns are there to help you, not hinder. A small part of being a good developer is knowing when to "break the rules". If MVVM is cumbersome for a task and you have determined the future value isn't worth the effort, then don't use the pattern. For example, as other posters have commented, why would you go through all the overhead to implement a simple about box?

Design patterns were never intended to be dogmatically followed.

Answer 4

No, it’s not pointless, but it is difficult to wrap your head around even though the pattern itself is ridiculously simple. There are tons of misinformation out there and various groups who battle over the proper way. I think with WPF and Silverlight you should use MVVM or you’ll be over coding and attempting to solve problems in a new model the “old” win forms methodology which just leads you into trouble. This is more the case in Silverlight since everything is required to be asynchronous (hacks around this are possible, but you should just pick another platform).

I’d suggest reading this article Simplifying the WPF TreeView by Using the ViewModel Pattern carefully to see how MVVM can be implemented well and allow you to change your win forms mentality to the new way of thinking in MVVM. In short when you want to get something done apply the logic to the ViewModel first not the View. You want to select an item? Change an icon? Don’t iterate over UI elements, just update the models properties and let data-binding do the nitty gritty.

Answer 5

I am in the middle of a quite complex MVVM development using PRISM so I already had to cope with this kind of concerns.

My personal conclusions:

MVVM vs MVC /PopUps & co

• MVVM is really a great pattern and in most cases it completely replaces MVC thanks to the powerful data binding in WPF
• Calling your service layer directly from the presenter is a legitimate implementation in most cases
• Even quite complex List /Detail scenarios may be implemented by pure MVVM thanks to the {Binding Path=/} syntax
• Nonetheless, when complex coordination between multiple views needs to be implemented, a controller in mandatory
• Events may be used; the old pattern which implies storing IView (or AbstractObserver) instances in the controller is obsolete
• The controller can be injected in each Presenter by IOC container
• Prism’s IEventAggregator service is another possible solution if the only use of the controller is event dispatching (in this case it can completely replace the controller)
• If views are to be dynamically created, this is a very well suited job for the controller (in prism the controller will get injected (IOC) a IRegionManager )
• Modal dialog boxes are mostly obsolete in modern composite applications, except for really blocking operations like mandatory confirmations; in these cases modal activation can be abstracted as a service called inside the controller, and implemented by a specialized class, which also allows for advanced presentation-level unit testing. The controller will, for example, call IConfirmationService.RequestConfirmation(“are you sure”) which will trigger a modal dialog display at runtime and can be easily mocked during unit testing

Answer 6

Getting this to work is difficult. In order to benefit from the MVVM pattern, you have to distribute code in several places throughout the layers of your application. You also have to use esoteric programming constructs like templates and lamba expressions.

For a commonplace modal dialog box? You are certainly doing something wrong there - MVVM implementation doesn't have to be that complex.

Considering you are new to both MVVM and WPF, it is likely you are using suboptimal solutions everywhere and unnecessarily complicate things - at least I did so when I first went WPF. Make sure that the problem is really MVVM and not your implementation before giving up.

MVVM, MVC, Document-View, etc. is an old family of patterns.. There are drawbacks, but no fatal flaws of the kind you describe.