Prism 8

Links

• Prism Library Documentation

Description

Fully open source version of Prism including MVVM, dependency injection, commands, EventAggregator, and others.
Prism 8 supports WPF, Xamarin Forms and UNO, but not Silverlight, Windows 8/8.1/WP8.1 or UWP.

Getting Started

• Nuget packages
  • Prism.Core
  • Prism.Wpf
  • Prism.DryIoc
• Prism Template Pack Visual Studio extension

App.xaml

App.xaml

<prism:PrismApplication x:Class="PrismFull.App" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:prism="http://prismlibrary.com/" > </prism:PrismApplication>

App.xaml.cs

public partial class App { protected override Window CreateShell() { return Container.Resolve<MainWindow>(); } }

ViewModels

ViewModels/MyViewModel.cs

public class MyViewModel : BindableBase { private string myProperty; public string MyProperty { get => myProperty; set => SetProperty(ref myProperty, value); } }

ViewModelLocator

Used to automatically wire the DataContext of a view to an instance of a ViewModel using a standard naming convention.

MyView.xaml

<!-- automatically wire the DataContext of MyView to an instance of MyApp.ViewModels.MyViewModel --> <UserControl x:Class="MyApp.Views.MyView" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:viewModels="clr-namespace:MyApp.ViewModels" xmlns:mvvm="http://prismlibrary.com/" mc:Ignorable="d" d:DataContext="{d:DesignInstance viewModels:MyViewModel}" mvvm:ViewModelLocator.AutoWireViewModel="True">

This convention assumes:

• that ViewModels are in the same assembly as the view types
• that ViewModels are in a .ViewModels child namespace
• that Views are in a .Views child namespace
• that ViewModel names correspond with View names and end with ViewModel

Commands

MyViewModel.cs

public DelegateCommand DoCommand { get; } public DelegateCommand DoWithParamCommand<string> { get; } public MyViewModel() { DoCommand = new DelegateCommand(Do, CanDo); DoWithParamCommand = new DelegateCommand<string>(DoWithParam, CanDoWithParam); } private void Do() { } private bool CanDo() => true; private void DoWithParam(string parameter) { } private bool CanDoWithParam(string parameter) => true;

MyView.xaml

<Button Command="{Binding DoCommand}" Content="Do" /> <Button Command="{Binding DoWithParamCommand}" CommandParameter="{Binding Content, RelativeSource={RelativeSource Self}}}" Content="Do" />

Parameter can't be of value type (int, double, bool, etc). Use instead the equivalent nullable type.

RaiseCanExecuteChanged

private bool isEnabled; public bool IsEnabled { get => isEnabled; set { SetProperty(ref isEnabled, value); SubmitCommand.RaiseCanExecuteChanged(); } }

ObservesProperty

Whenever the value of the supplied property changes, the DelegateCommand will automatically call RaiseCanExecuteChanged to notify the UI of state changes.

DoCommand = new DelegateCommand(Do, CanDo).ObservesProperty(() => IsEnabled);

ObservesCanExecute

If your CanExecute is the result of a simple Boolean property, you can eliminate the need to declare a CanExecute delegate, and use the ObservesCanExecute method instead. ObservesCanExecute will not only send notifications to the UI when the registered property value changes but it will also use that same property as the actual CanExecute delegate.

DoCommand = new DelegateCommand(Do).ObservesCanExecute(() => IsEnabled);

Task-Based DelegateCommand

DoCommand = new DelegateCommand(DoAsync); async void DoAsync() { await SomeAsyncMethod(); }

Dependency Injection

App.xaml.cs

public partial class App { protected override void RegisterTypes(IContainerRegistry containerRegistry) { // register a singleton service containerRegistry.RegisterSingleton<IMyService, MyService>(); // registera transient service containerRegistry.Register<IMyService, MyService>(); }

singleton service	for a service which is used throughout the application and that retains its state.
transient service	create a new instance each time.
scoped service	no implementation because unlike a web application, desktop applications are dealing with a single user and not scoped user requests.

Event Aggregator

Event mechanism that enables communications between loosely coupled components in the application.

MyApp.Shared/MyPayload.cs

public sealed class MyPayload { public string Prop1 { get; set; } public string Prop2 { get; set; } }

MyApp/MyViewModel.cs

internal sealed class MyViewModel { IEventAggregator eventAggregator; public MyViewModel(IEventAggregator eventAggregator) { this.eventAggregator = eventAggregator; } // publishing an event var payload = new MyPayload { Prop1 = "value1", Prop2 = "value2", }; eventAggregator.GetEvent<PubSubEvent<MyPayload>>().Publish(payload); // subscribing to events eventAggregator.GetEvent<PubSubEvent<MyPayload>>().Subscribe(MyAction); void MyAction(MyPayload payload) { } }

Subscribing on the UI Thread

If the subscriber needs to update UI elements in response to events, subscribe on the UI thread. In WPF, only a UI thread can update UI elements.

eventAggregator.GetEvent<MyEvent>().Subscribe(DisplayMessage, ThreadOption.UIThread);

PublisherThread	use this setting to receive the event on the publishers' thread. Default value.
UIThread	use this setting to receive the event on the UI thread.
BackgroundThread	use this setting to asynchronously receive the event on a .NET Framework thread-pool thread.

In order for PubSubEvent to publish to subscribers on the UI thread, the EventAggregator must initially be constructed on the UI thread.

Subscription Filtering

eventAggregator.GetEvent<MyEvent>().Subscribe(DisplayMessage, ThreadOption.UIThread, false, x => x == "KeyMessage");

Performance concern

var keepSubscriberReferenceAlive = true; var myEvent = eventAggregator.GetEvent<MyEvent>(); myEvent.Subscribe(DisplayMessage, keepSubscriberReferenceAlive); myEvent.Unsubscribe(DisplayMessage);

keepSubscriberReferenceAlive

true	the event instance keeps a strong reference to the subscriber instance, thereby not allowing it to get garbage collected. For information about how to unsubscribe, see the section Unsubscribing from an Event later in this topic.
false	default value. The event maintains a weak reference to the subscriber instance, thereby allowing the garbage collector to dispose the subscriber instance when there are no other references to it. When the subscriber instance gets collected, the event is automatically unsubscribed.