What's New in Prism Library 5.0 for WPF

From: Developer's Guide to Microsoft Prism Library 5.0 for WPF

Prism 5.0 includes guidance in several new areas, resulting in new code in the Prism Library for WPF, new and updated QuickStarts, and updated documentation. Parts of the Prism Library changed between Prism 4.1 and Prism 5.0 to support the new guidance, fix existing issues, and respond to community requests.

Note: For .NET 4.0, Silverlight, or Windows Phone 7.x applications use Prism 4.1.

New Guidance

Prism 5.0 contains several areas of new guidance as follows:

• Prism.Mvvm is a portable class library that encapsulates Prism’s MVVM support. This library includes ViewModelLocationProvider. Views and view models can be wired up together using the new ViewModelLocationProvider’s convention-based approach as explained in Implementing the MVVM Pattern. View model construction can be accomplished using a dependency injection container. The ViewModel Locator’s extensibility points are discussed in Extending the Prism Library. DelegateCommands are now extendable and provide Async support. A new implementation of the INotifyPropertyChanged interface, the BindabaleBase class, was added.
• The PopupWindowAction class was added to the Prism.Interactivity assembly to open a custom window in response to an interaction request being raised.
  The InvokeCommandAction action provided by Prism now passes trigger parameters to the associated command.
  For more information see Advanced MVVM Scenarios.
• The EventAggregator classes have been moved to the Prism.PubSubEvents portable class library.
• The NavigationParameters class can now be used to pass object parameters during navigation, using the overloads of the RequestNavigate method of a Region or RegionManager instance.

Changes in the Prism Library

Prism Library 5.0 includes changes related to new functionality, code organization, and APIs.

Code Organization

The following organizational changes were made to the library:

• The Microsoft.Practices.Prism.PubSubEvents portable class library contains PubSubEvents, EventAggregator and related classes.
• The Microsoft.Practices.Prism.Mvvm portable class library contains ViewModelLocationProvider, BindableBase, ErrorsContainer, PropertySupport, CompositeCommand, DelegateCommand, DelegateCommandBase, and WeakEventHandlerManager.
• The Microsoft.Practices.Prism.Mvvm.Desktop assembly contains the WPF ViewModelLocator attach property.
• The EventAggregator classes are marked obsolete in the Prism assembly.
• The Silverlight and phone versions of the Prism Library were taken out. If you need these libraries download the Prism 4.1 assemblies from NuGet.
• Prism and Prism.Mvvm are independent of each other but share IActiveAware. Therefore IActiveAware has been moved to Prism.SharedInterfaces.

In version 5.0 of Prism, Pub Sub Eventing functionality was moved into a separate assembly (Prism.PubSubEvents). DelegateCommand, CompositeCommand, and ViewModel support were moved into another assembly (Prism.Mvvm). There are many advantages to separating PubSubEvents and Mvvm from the core Prism assembly.

• You can select only the functionality that you need. If you want Regions and Modularity, you use the core Prism assembly. If you want only ViewModel and commanding support, you use Prism.Mvvm. If you only want Pub Sub Eventing, you use Prism.PubSubEvents. Each assembly is smaller and easier to understand.
• You can now build your ViewModel code in a portable class library that leverages Prism.Mvvm and/or Prism.PubSubEvents since both are PCLs. By putting your ViewModel code in a PCL, your ViewModel code is constrained to using dependent libraries that are platform agnostic and thus can target multiple platforms.
• Updates to these smaller libraries can be made more easily and quickly.

API Changes

The Prism Library API changed in several key areas. The bootstrapper was heavily modified and reusable code was added to support the new areas of guidance provided in Prism.

MVVM and Event Aggregator Changes.

Moving ViewModel and EventAggregator to a PCL causes several changes to the Prism Library. These changes include the following:

• The BindableBase class in Prism.Mvvm should be used instead of NotifcationObject. The NotificationObject and PropertySupport classes are marked obsolete in the Prism assembly.
• When inheriting from the BindableBase class, use the SetProperty method to update the property's backing field and raise the corresponding property change event. A new OnPropertyChanged method that takes a lambda expression as a parameter has been added.
• Use the PubSubEvents class in the Microsoft.Practices.PubSubEvents portable class library instead of CompositePresentationEvents. The classes from the Events solution folder in the Prism assembly are marked obsolete.
• The UriQuery class was renamed to NavigationParameters, it keeps the same functionality as before, and adds support for passing object parameters.
• DelegateCommand includes support for async handlers and has been moved to the Prism.Mvvm portable class library. DelegateCommand and CompositeCommand both use the WeakEventHandlerManager to raise the CanExecuteChanged event. The WeakEventHandlerManager must be first constructed on the UI thread to properly acquire a reference to the UI thread’s SynchronizationContext.
• EventAggregator now must be constructed on the UI thread to properly acquire a reference to the UI thread’s SynchronizationContext.
• The WeakEventHandlerManager is now public.
• The Execute and CanExecute methods on DelegateCommand are now marked as virtual.

Additions to the Prism Library Core API

The following namespaces were added to the Prism Library to support the new areas of guidance added in Prism 5.0:

• Microsoft.Practices.Prism.PubSubEvents was added to help you send loosely coupled message using a portable class library.
• Microsoft.Practices.Prism.Mvvm was added to assist you in implementing MVVM using a portable class library and several platform specific libraries.
• Microsoft.Practices.Prism.SharedInterfaces has been added to share the IActiveAware interface between Prism and Prism.Mvvm assemblies, therefore the IActiveAware interface has been moved to this assembly. It is also intended for future use.

CodePlex Issues Resolved

• 8532: InteractionRequestTrigger can cause memory leaks with some implementations.
• 9153: 'Notification' really should be an interface.
• 9438: Navigation to an existing view.
• 5495: Event to Command.
• 8101: DelegateCommand is not extendable.
• 5623: Make WeakEventHandlerManager public.
• 9906: A bug when using XAML module catalog in WPF.
• 7215: Issue with ModuleCatalog.CreateFromXaml for WPF application with MEF Bootstrapper.
• 8703: RegionManager::IsInDesignMode.
• 4349: Default Region Behavior Order Problem.
• 3552: Region manager in V2 fails to recognize non-WPF applications.

Example Code Changes

Prism 5.0 contains eleven separate code samples that demonstrate portions of the provided guidance. Several samples from Prism 4.1 were removed or replaced, and new samples added.

The following samples were added for Prism 5.0:

• Basic MVVM QuickStart. This QuickStart shows a very simple MVVM application that uses the ViewModel Locator and show a parent and child ViewModels. For more information, see the MVVM QuickStart**.**
• MVVM QuickStart. This QuickStart was removed for this version.
• MVVM Reference Implementation. This reference implementation was removed for this version.
• View-Switching Navigation QuickStart. This QuickStart now supports WPF. It demonstrates how to use the Prism region navigation API. For more information, see View-Switching Navigation QuickStart.
• State-Based Navigation QuickStart. This QuickStart now supports WPF. It shows an approach that uses the Visual State Manager to define the views (states) and the allowed transitions. For more information, see State-Based Navigation QuickStart.
• UI Composition QuickStart. This QuickStart now supports WPF. It replaced the View Injection QuickStart and the View Discovery QuickStart from Prism 2.0. In the current versions, both concepts are shown in one example application. For more information, see UI Composition QuickStart.
• Interactivity QuickStart. This new QuickStart demonstrates how to exposes an interaction request to the view through the view model. The interactions can be a popup, confirmation, custom popup, and a more complex case where the popup needs a custom view model. It also shows Prism’s InvokeCommandAction action that passes the EventArgs from the trigger, as a command parameter. For more infromation, see Interactivity QuickStart.

NuGet Packages Now Available

In your application, you can now use NuGet to add references to the Prism assemblies. These packages include:

• Prism
• Prism.Composition
• Prism.Interactivity
• Prism.Mvvm
• Prism.PubSubEvents
• Prism.UnityExtensions
• Prism.MEFExtensions

More Information

For more information about how to upgrade a solution from version 4.1 to version 5.0 of the Prism Library, see Upgrading from Prism Library 4.1.

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