Advanced Topics for Building Large-Scale Applications with Microsoft SilverlightJohn PapaSenior Technical EvangelistMicrosoft Corporation

CL22

Outline> MVVM

> Model – View – ViewModel> What it does> Where it works well> Variations

> Prism> Enabling MVVM> Filling the gaps> Options

Goals> Understand MVVM’s Role in Silverlight

> Many ways to accomplish your goal> See it in Action> Learn about MVVM Enablers

> Prism> Roll Your Own

Another MC_ Acronym?> MVVM> MVC> MVP> MV????

> Commonly accepted patterns for maintainable, scalable applications

MVVMThe What and Why> Separation of concerns> View = handles UI> Model = contains the pure data > ViewModel = communicates between

View and Model through bindings> Works GREAT for Silverlight and WPF

> XAML based data bindings> Testable

The MVVM TriadPutting it Together

ViewModel

View

Model

> Display data in Controls

> UI Friendly Entities, UI State, Actions

> Entities representing data

ModelMVVM> Represents the data> The entity> Not required to know where it gets its

data from> From a WCF service. WCF RIA Services,

etc> May contain validation

ViewMVVM> The screen, the UI, the UserControl in

Silverlight> Handles UI look and feel> Presentation of information> Communicates with ViewModel

through bindings

ViewModelMVVM> Main source of logic for the MVVM triad> Connects the Model to the View> Abstracts the View> Public properties that are bound to a View> INotifyPropertyChanged and

INotifyCollectionChanged talk to the View through bindings

> Listens for changes from the View through bindings

> Invokes services to communicate outside the MVVM triad

Which Way Do I Go?MVVM Variations> View must be paired with a ViewModel

somehow> Several workable options> Maintain the spirit of each of the

components of the MVVM triad

View First MVVM Variations> ViewModel is declared as a Static

Resource in the View’s XAML> Works well in Expression Blend

> Another way is to create ViewModel in the View’s code-behind

View First MVVM

demo

ViewModel FirstMVVM Variations> View is injected into the ViewModel’s

constructor > Example:

> ViewModel is created then the View is created using Dependency Injection

View and ViewModel MarriageMVVM Variations> View must be paired with a ViewModel

somehow> ViewModel and View are created

through an intermediary, then paired together

Marrying the View to the ViewModelvm = new MyVM();view = new MyView();view.DataContext = vm;

// With Unityvm = container.Resolve<IMyVM>();view = container.Resolve<MyView>();

view.DataContext = vm;

Prism 2Be Picky> Prism is a set of options> Use what you want and ignore the rest

> Example: > Choose Modules and Commanding, but ignore

Event Aggregation and Regions

Prism Technical Concepts

Container

Commands

Bootstrapper

Regions

Modules

Event Aggregation

Unity and DI

Shell

BootstrapperLet’s Get this Party Started!> Kicks off the application> Starts the main UI container (the

Shell)> Registers Modules and loads, if

needed> Registers any global singletons

(optional)> Usually contained in the “Bootstrapper

project”

ShellThe Main View> The main UI container> Houses all of the Views that will be

loaded> Can be split into Regions> Knows nothing of what will be loaded

into it

RegionsContent Areas > Area(s) in the Shell where Views can

be placed> Given a name> Can contain context, if needed> RegionManager exists to help

maintain Regions

ModularitySelf Contained Modules> To the user this is seamless> Developed separately> Do not reference other modules> Solution is split into Modules > Example:

> City government application> Module 1: Managing land parcels> Module 2: Traffic light administration> Module 4: City Parks

> Modules share infrastructure and Models

Dependency InjectionUsing Unity> Unity or other DI Tools (Ninject)> Testability and mocking> Abstraction

> Container object allows classes to be registered against their interfaces

> When an interface is requested, the container creates the class registered with the interface

> Supports singletons, too

Register the Interface to the Class

container.RegisterType<IMyViewModel,

MyViewModel>();

Create the Concrete Class

container.Resolve<IMyViewModel>();

InfrastructureCommon Tools> A Silverlight class library project> Contains shareable items for the

modules> Classes> Assets> Resources

> Makes no references> A pure library

CommandingActions and Reactions> Allows events between a View and a

ViewModel through Data Binding> ViewModel declares the Command

receiver> Command is declarative in XAML

> Button - Click> ListBox (Selector) – Selected

> Command is data bound to the ViewModel’s command receiver

> Can be disabled/enabled based on rules

Event AggregatorPublisher and Subscriber > Allows events of any kind to be

published and subscribed to> Can be cross module> Can be filtered by subscribers> For example:

1. Click on a menu item in the Shell2. Event is invoked by the publisher3. Event is received by the subscriber4. The subscriber then loads a View in a

Region in the Shell

InfrastructureCommon Tools> Infrastructure is a Silverlight class

library project> Contains classes, assets, resources

that are shared amongst the Modules> Does not reference any modules> Does not make calls to web services> It’s a pure library

Modular MVVM and Prism

demo

Screen Presentation EnablerEnabling Screens> Must be able to navigate between

screens> Views do not know about each other> Roll Your Own Screen Conductor

> Loading/unloading> Displaying/hiding> Can I Leave?> Clean yourself up!

Screen Presentation FrameworkKey Players> Screen

> Manages the MVVM triad> ScreenFactory

> Creates a Screen class> ScreenFactoryRegistry

> A ScreenFactory directory> ScreenConductor

> Listens for & acts upon screen activation events

> ScreenCollection> Collects screens

Screen Conductor

demo

Resources> My blog: http://www.johnpapa.net > Twitter: @john_papa

> Prism from Patterns and Practices > http://www.codeplex.com/prism

> Article on the Screen Presentation Framework, MVVM and Prism > Coming soon to MSDN Online

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