MVVM and Prism


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This presentation deals with basic understanding of MVVM and Prism.

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MVVM and Prism

  1. 1. 0
  2. 2. Agenda • MVVM • PRISM
  3. 3. MVVM Model-View-ViewModel
  4. 4. 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
  5. 5. 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.
  6. 6. 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.
  7. 7. 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
  8. 8. MVVM Layers Connections View ViewModel Model • 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
  9. 9. 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.
  10. 10. MVVM Execution • What happens when an user clicks a Button? 1. 2. 3. The View fires event that a button was clicked The View calls a Method in the ViewModel The ViewModel gets/sets some data from/in the Model User Fires an Event View The ViewModel requests data ViewModel The View Shows the new data The ViewModel receives data Model
  11. 11. 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
  12. 12. INotifyProperyChanged • The INotifyPropertyChanged interface contains only one event PropertyChanged(object sender, PropertyChangedEventArgs e) • 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
  13. 13. 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
  14. 14. 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?
  15. 15. 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
  16. 16. IOC Frameworks • StructureMap • Unity • Managed Extensibility Framework (MEF)
  17. 17. Infrastructure Services • • • • • • • IOC Container NavigationService EventAggregator SessionStateService FlyoutService Service Proxies Other objects that are needed application wide
  18. 18. ViewModel Auto Wire-up • Resolve( ) • ViewModelLocator. SetDefaultViewTypeToViewModelTypeResolver • Persistence • If you can’t use Auto Wire-up • Declarative wire-up • Programmatic wire-up
  19. 19. Commands • • • • • Delegate Commands Synchronous Command Execution Asynchronous Command Execution Command Parameters Conditional Command Execution
  20. 20. 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
  21. 21. Model Validation (Contd.)
  22. 22. Useful Links • •
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