Real-world MVVM in WPFPaul Stovell

Senior ConsultantTechnical specialist: WPF

Agenda

Part 1: Introducing MVVM• Refactoring to MVVM• Unit testing MVVM• Commands

Part 2: Formalizing MVVM• History• Model-View-ViewModel• ViewModel-First

Part 3: Playing with Others• Navigation• Composition• Communication

About You

• Awesome coder• Know some WPF• Love binding!

This is you...

Introducing MVVMPART 1

Demo

Refactoring to MVVM

Demo

Unit testing MVVM

What did we just do?

• Employee = the Model• SearchView.xaml = the View• SearchViewModel = the ViewModel

Demo

Using Commands

Demo

New requirement: search-as-you-type

Formalizing MVVMPART 2

History

Martin Fowler

John Gossman

MVVM

Presentation Model

Model-View-ViewModel

View ViewModel External services

CommandsMethods

public void Search(){}

ICommand Search { get;set; }

void Button_Click(...){ viewModel.Search();}

<Button Command="{Binding Search}" />

Properties

Events

Model-View-ViewModel

View ViewModel External services

CommandsMethods

public string SearchText { get { ... } set { ... Search(); }}

<TextBox Text="{Binding SearchText}" />

Properties

Events

Model-View-ViewModel

View ViewModel External services

CommandsMethods

public event EventArgs SessionClosed;

viewModel.SessionClosed += (s,e) => Close();

Properties

Events

ViewModel-First MVVM

View ViewModel External services

CommandsMethods

View.Close();

ViewModel.Search();

Properties

Events

ViewModel-First MVVM

View ViewModel External services

CommandsMethods

public event EventHandler SessionClosed;

public event EventHandler SearchRequested;

Properties

Events

Model-View-Presenter

View Presenter External services

Methods

public event EventHandler SearchRequested;

Eventsprivate void View_SearchRequested(...){ // Do search}

Model-View-Presenter

View Presenter External services

Methods

View.ShowResults(results);

public void ShowResults(List<SearchResult> results){ listBox1.ItemsSource = results;}

Events

The Model

• Service messages/DTO’s• Domain entities/value objects• DataSets• LINQ to SQL objects

Or:

• View-specific objects mapped from above

Instantiation and wire-up

public CalculatorView(){ InitializeComponent(); DataContext = new CalculatorViewModel(); }

• Internal creation:

Instantiation and wire-up

public CalculatorView(CalculatorViewModel model){ InitializeComponent(); DataContext = model; }

• ViewModel as a dependency:

var viewModel = new CalculatorViewModel();var view = new CalculatorView(viewModel);

Instantiation and wire-up

<UserControl ...> <UserControl.DataContext> <local:CalculatorViewModel /> </UserControl.DataContext>

• ViewModel via XAML:

Instantiation and wire-up

• 5 more ways:http://is.gd/dv7aN

Playing with OthersPART 3

Navigation

1. INavigator.Navigate(...)2. Event

View+ViewModel

View

ViewModel

URI

Demo

• Adding navigation with Magellan

Composition

Shell ViewModel

Search ViewModel

Weather ViewModel

ShellSearch

Weather

Composition

Order ListTop Region

Bottom Region

Bottom-Up

Search Weather

Infrastructure

1. Resolve

2. Place

Inter-view Communication

Standard .NET events

Search View Model

Results View Model

Criteria View Model

1. Child model raises event2. Parent model forwards

event

Inter-view Communication

Results ViewModel

Criteria ViewModel

Hub

Publish Handle

Advert ViewModel

Handle

Recent Searches

ViewModel

Publish

Mediator (e.g., Prism EventAggregator)

bus.Publish(new SearchMessage(searchText));

bus.Subscribe<SearchMessage>(HandleSearch);

Conclusion

• MVVM is about separation of concerns– View has UI-specific code– VM has behaviour and state– Behaviour = methods/commands– State = properties

• Separation of concerns makes code easy to test

• It’s easy: just one extra class!

What’s next?

• Inversion of Control containers• Modular applications• Pub/sub messaging• Inductive user interfaces• p&p Prism

Links

• MVVM Light: http://is.gd/duX2Q• Caliburn: http://is.gd/duX5L• More: http://is.gd/duWWG• Magellan: http://is.gd/duX70• Reuxables: http://is.gd/duX8G

Thanks!

Paul Stovellpaul.stovell@readify.net

www.paulstovell.com

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