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Agenda• MVVM• PRISM

MVVMModel-View-ViewModel

What is MVVM

• MVVM is a design pattern

• MVVM stands for Model-View-ViewModel

• Design patterns are a set of guidelines

• Design patterns are Not a set of rules

MVC vs MVVM• MVC – The view sits at the top of the architecture, the

controller sits below the view. The model sits below the controller. So the view knows about the controller, the controller knows the model. The view is notified when the model changes.

• MVVM – The controller is replaced with a view model. the view model sits below the UI layer. The view model exposes the data and command objects that the view needs. You could think of this as a container object that view goes to to get its data and actions from. The view model pulls its data from the model below.

What is MVVM• MVVM is a three-layer architectural pattern• Mostly used in Windows 8, WPF and Silverlight applications.• Used to separate presentation logic from business logic.

• MVVM makes it easier• For the developer and the front-ender to work on the same

project.• Change the presentation layer at any point.• Extend the project with less difficulties.• Testing components.

MVVM Architecture• MVVM consists of three layers• View is the Presentation Layer

• Contains only GUI elements, but no functionality• Model refers to

• An object model that represents the real state content• A data access layer that represents that content

• ViewModel is a "Model of the View"• Abstraction of the View• Serves in data binding between the View and the Model• Acts as a data binder/converter• Changes Model information into View information• Passes commands from the View into the Model• Exposes public properties, commands, and abstractions

MVVM Layers Connections

• The main idea of MVVM is that each pair of layers is coupled as loosely as possible• The View only knows about the ViewModel

• The View has no idea of the Model• The ViewModel only knows about the Model

• The ViewModel has no idea of the View• The Model knows nothing about the other layers

View ViewModel

Model

Loosely Coupled

• The View knows the ViewModel but the ViewModel does not know the View.• You can very easily replace the View without affecting

the ViewModel. • This is very useful in Developer/Designer teams where

the Developer improves the ViewModel and the Designer enhances the View.

MVVM Execution• What happens when an user clicks a Button?

1. The View fires event that a button was clicked2. The View calls a Method in the ViewModel3. The ViewModel gets/sets some data from/in the Model

View ViewModel

Model

User Fires an Event

The ViewModel requests data

The ViewModel receives data

The View Shows the new

data

ViewModel Implementation• A question pops out• How does the View know about changes in the ViewModel?• How the ViewModel knows about changes in the Model?• There is no reversed connection, right?

• The answer is simple• The INotifyPropertyChanged interface

• Gives an event to notify about changes

INotifyProperyChanged

• The INotifyPropertyChanged interface contains only one event

• The point of this event is to be called when the data is changed

• Both Model and ViewModel should implement this interface

• In small project only the ViewModel can implement it

PropertyChanged(object sender, PropertyChangedEventArgs e)

Prism-RT• WPF• Microsoft Patterns & Practices Guidelines• Prism 1,2,3,4• Prism for Windows-RT• Inversion of Control• Delegate Commands• Model Validation• Navigation• …And more

Inversion of Control• How does normal control flow look like?• Inverted Flow?• Common in Framework Extensions• Inevitable if you want to build loosely coupled modules• But How to decide which module gets the call?

Dependency Injection• Caller doesn’t have to know the callee• Dependency resolution not caller’s headache anymore• Interaction is now based on defined interfaces• Types of DI• Constructor Injection*• Setter Injection• Interface Injection

IOC Frameworks• StructureMap• Unity• Managed Extensibility Framework (MEF)

Infrastructure Services• IOC Container• NavigationService• EventAggregator• SessionStateService• FlyoutService• Service Proxies• Other objects that are needed application wide

ViewModel Auto Wire-up• Resolve( )• ViewModelLocator.

SetDefaultViewTypeToViewModelTypeResolver• Persistence• If you can’t use Auto Wire-up• Declarative wire-up• Programmatic wire-up

Commands• Delegate Commands• Synchronous Command Execution• Asynchronous Command Execution• Command Parameters• Conditional Command Execution

Model Validation• ValidatableBindableBase• BindableValidator• Annotation Attributes• When to Validate• When property value is set?• When a command is fired?

• Error Message Binding• Restoring Error State

Model Validation (Contd.)

Useful Links• http://

msdn.microsoft.com/en-us/library/windows/apps/hh465099.aspx

• http://msdn.microsoft.com/en-us/library/windows/apps/br229566.aspx

Good Luck