WPF Best Practices: Do custom controls work well with the MVVM design?

Question

I was looking at creating a common control that I will be able to reuse on my pages: an AddressControl which has Address1, Address2, City, State, Zip, etc...

Originally I just created a class (AddressEntity) that contained all these items and implemented INotifyPropertyChanged. I included that class as a DependencyProperty in my Code-Behind for the AddressControl and used it as the DataContext for the bindings to its properties.

Then, someone said my code was ugly and I should look into MVVM. Looking at it, I assume that:

• AddressEntity.cs will just be a container of data (i.e. Address1, Address2, etc.) and members (i.e. Clone, ToString, etc.)
• I need some AddressViewModel to wrap my AddressEntity in and provide the PropertyNotification Changes, Validation, etc.
• I need to somehow have a "View" for this.

The problem is every example I've ever seen has a UserControl as the View and not a CustomControl. Before I delve too deep into this...

• Is it possible to use MVVM + Custom Controls for this example?
• Is it pretty much the same thing (UserControl vs CustomControl) as the View with the exception of primary differences of UserControl vs CustomControl? Basically, is my CustomControl really just a View?

References: The Model-View-ViewModel (MVVM) Design Pattern for WPF

Answer 1

CustomControls are never done with mvvm.

What you want is a reusable view(user control) of your data and not a control(custom control).

UserControls and CustomControls are two completely different beasts.

EDIT:

Notwithstanding why UserControls were originally developed, in MVVM typically you use a UserControl when you want a reuseable view which is specific to your model/viewmodel. Its just XAMl without any code behind (except for the auto generated InitializeComponent stuff). Generally you keep a UserControl in the same project that you use it in.

You go for a CustomControl when you want a generic piece of functionality which requires a view and which has potential use even outside the scope of your current application. Here the control is actually defined in a code file and the look (which can be overriden) comes via XAML in a resource dictionary. Generally you keep a CustomControl in a a seperate ControlLibrary project and reference the library in the project you wish to use it in.

With due respect to WallStreetProgrammer, choosing between a user control and a custom control based solely on whether or not you want a lookless control is a bit naive.

Answer 2

When using MVVM the Model and ViewModel should not be dependent on the View, that is they should not care what kind of view use them.

The difference between a custom control and a usercontrol in WPF is that the custom control is lookless and can be customized via its ControlTemplate. This is what you should write if you are writing a generic control library, like Microsoft does. If you however have a specific look in mind for you control, just go with a user control, it is much faster but will only have one look, the one you define for it.

It is common to use a mix of custom controls and user controls in a MVVM project. For example you would probably use a bunch of custom controls from Microsoft (like textboxes and textblocks) and combine them into user controls.

See Control Authoring Overview