Understanding the MVVM pattern Laurent Bugnion Senior User Experience Integrator IdentityMine http://[blog|www].galasoft.ch

Model – View – ViewModel « MVVM in a SLOOB with SLUT » What is MVVM? A weird acronym Model – View – ViewModel « MVVM in a SLOOB with SLUT » Woven into WPF/SL Some confusion: MVVM is really just the pattern The rest are helpers, practices, etc

The MVC pattern Model View Controller

The Passive View pattern Model View Controller

The Presentation Model pattern View DataBinding Presentation Model (ViewModel)

Testability, Maintainability, Blendability “The ability to be edited in Blend” (and Visual Studio designer…) Differentiate code in design and runtime Create design time data

Hello MVVM (and Hi Blend) Demo of connection to WCF service, fails in Blend Show how to attach to process Identify problem IsInDesignMode

Bridging the gap View DataBinding Commands Messages ViewModel Model

View ViewModel View ViewModel View ViewModel Bridging the gap View ViewModel View ViewModel Messages View ViewModel Messages + callback

“Point of entry” for a method” Can be data bound ICommand interface Commands “Point of entry” for a method” Can be data bound ICommand interface Execute method CanExecute method CanExecuteChanged event handler

Commands and RelayCommands Demo of connection to WCF service, fails in Blend Show how to attach to process Identify problem IsInDesignMode

RelayCommands RelayCommand MyCommand = new RelayCommand( () => ..., () => true | false); RelayCommand<T> MyGenericCommand = new RelayCommand<T>( p => ..., p => true | false);

Should be simple by default Possible to open filtered channels Messaging Should be simple by default Possible to open filtered channels To a target Type (or an Interface) With a Token With various Messenger instances No constraints at all

Messaging Demo of connection to WCF service, fails in Blend Show how to attach to process Identify problem IsInDesignMode

Messaging Messenger.Default.Register<T>( this, p => DoSomething(p)); Messenger.Default.Send<T>(p);

“Breaking the monotony” http://www.galasoft.ch/mvvm/getstarted MVVM Light Toolkit “Breaking the monotony” http://www.galasoft.ch/mvvm/getstarted http://mvvmlight.codeplex.com V3 released at MIX10 Keep it small Keep it simple

ESSENTIALS RelayCommand Messenger ViewModelBase EXTRAS EventToCommand MVVM Light Libraries V3 ESSENTIALS RelayCommand Messenger ViewModelBase EXTRAS EventToCommand DispatcherHelper

Project templates (VS + Blend) Item templates (VS + Blend) MVVM Light Tools V3 Project templates (VS + Blend) Item templates (VS + Blend) Code snippets

MVVM Light Toolkit, Unity, Blendability Demo of connection to WCF service, fails in Blend Show how to attach to process Identify problem IsInDesignMode

INotifyPropertyChanged Commands Flaws of MVVM Too much code needed INotifyPropertyChanged Commands Some operations are tricky (set focus…) Not applicable to ASP.NET, etc Message to community is not clear

“No code in the code behind” Debunking the myths “No code in the code behind” “If you put code in the View's code-behind, the MVVM police will take your family away” “No need for converters” “MVVM is only suitable for big projects” “MVVM costs performance” “MVVM is complex / makes my head hurt”

“I don’t need separation because I don’t have a designer” Debunking the myths “I don’t need separation because I don’t have a designer” “You cannot use MVVM with other patterns” “MVVM will make you rich and attractive”

MVVM on the Windows Phone 7 Demo of connection to WCF service, fails in Blend Show how to attach to process Identify problem IsInDesignMode

Thanks @LBugnion http://blog.galasoft.ch http://www.galasoft.ch/mvvm/getstarted @LBugnion