Introduction to MVVM presented at the NYC .Net meetup on 2011-02-15.

1. Boulos Dib
Independent Consultant
Napeague Inc.
February 15, 2011

2.  A pattern that describes how UI components
interact with other application code.
 Associated with Microsoft XAML platforms
(Silverlight, WPF)
 MVVM is not complicated, really!!!, simple is
good.

3.  Not a framework nor an implementation, just a
reusable solution to a commonly occurring
problem.
 May not apply to every application type, only you
can determine that for your application type.
 MVVM is not required for Silverlight and MVVM,
but can help where applicable.
 It should not slow down development. If it does,
re-factor your approach, something else is off.

4.  Separation of concerns
◦ Each component has a specific role. UI Code is not
mixed with Business logic.
 Natural Patterns for XAML Variants
◦ Microsoft’s XAML is designed with MVVM support in
mind (Key Enabler: DataBinding).
 Enables Developer-Designer Workflow
◦ For some shops, this is long time overdue
◦ XAML/Expression/Other = Designer, Code=Developer,
XAML+Code=Integrator
 Better Testability
◦ User Interface Business Logic can (and should) be tested.
Leave UI Component testing to Microsoft or Third Party
Component Vendors.

5.  MVVM Components
◦ Model
◦ View
◦ ViewModel
 Each serves a distinct and separate role.
 Components are decoupled from each other:
◦ Allowing for components to be swapped
◦ Allowing internal implementation to be changed without
affecting the others
◦ Allowing components to be worked on independently
◦ Enabling isolated unit testing

6.  Business Logic and Data
◦ Business Objects, Services, Data Access Layers.
 Implements Change Notification for
properties.
◦ INotifyProperyChanged – Individual Property
◦ INotifyCollectionChanged – Collections
 Include ObserableCollection in your daily routine.
 Responsible for Model-level validation
◦ IDataErrorInfo
 Independently Unit-Testable Code.

7.  Defines the User Interface Elements (What the
user sees and interacts with)
◦ UserControl, Form, Window, DataTemplate
 Could be a top level component or a sub-
component
◦ Custom Controls, Multiple Tabs, Wizard
 May have some code-behind.
 DataContext is the ViewModel
 Controls bind to ViewModel Public Properties
 Behaviors can invoke ViewModel Public
methods.

8.  Responsible for UI Logic and Data for View
 Layer of abstraction between View and Data
Model.
 Can expose ICommand for Views
 Public Methods are usable by View Behaviors
 Uses DataBinding to maintain and
communicate state with the View.
 Implements Change Notifications.
 Independently Unit-Testable Code

9.  Code Behind
◦ View.DataContext = ViewModel
 XAML
◦ StaticResource
◦ ViewModelLocator
◦ DataTemplate

10.  Command
◦ Entry into a method – actually a property
◦ Implementation of ICommand
 Execute
 CanExecute
 CanExcuteChanged - Event
 RelayCommand

11.  ViewModel  View
 ViewModel  ViewModel

12.  MVVM Light – Laurent Bugnion
◦ http://mvvmlight.codeplex.com/
 Cinch – Sacha Barber
◦ http://cinch.codeplex.com/
 Caliburn – Rob Eisenberg
◦ http://caliburn.codeplex.com/
 Jounce – Jeremy Likness
◦ http://jounce.codeplex.com/
 MVVM Foundation – Josh Smith
◦ http://mvvmfoundation.codeplex.com/