Prism 8

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Description

Fully open source version of Prism including

  • MVVM
  • Commanding: DelegateCommand
  • Messaging: EventAggregator
  • Navigation
  • Dialog services
  • Modularity
  • Dependency injection

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.Unity dependency injection containers
Adding Prism.DryIoc will add Prism.Wpf and Prism.Core

Prism Template Pack Visual Studio extension

  • Templates
    • Prism Blank App (.NET Core) - target .NET Core 3.1
    • Prism Blank App (WPF) - target .NET Framework 4.7.2
    • Prism Blank App (Uno plateform)
  • Snippets
    • propp property which notifies its changes
    • cmd cmdfull delegate command
    • cmdg cmgfull delegate command with parameter

App.xaml

  • Shell: the main / root window
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>();
    }

    protected override void RegisterTypes(IContainerRegistry containerRegistry)
    { }
}

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:prism="http://prismlibrary.com/"
             mc:Ignorable="d"
             d:DataContext="{d:DesignInstance viewModels:MyViewModel}"
             prism: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

Change the naming convention

App.xaml.cs 
protected override void ConfigureViewModelLocator()
{
    base.ConfigureViewModelLocator();

    ViewModelLocationProvider.SetDefaultViewTypeToViewModelTypeResolver((viewType) =>
    {
        var viewName = viewType.FullName;
        var viewAssemblyName = viewType.Assembly.FullName;
        var suffix = viewName.EndsWith("View") ? "Model" : "ViewModel";
        var viewModelName = $"{viewName.Replace(".Views.", ".ViewModels.")}{suffix}, {viewAssemblyName}";

        var assembly = viewType.Assembly;
        return Type.GetType(viewModelName, true);
    });
}

Custom ViewModel registration

Faster because it doesn't use reflexion.

ModuleAModule.cs 
public void RegisterTypes(IContainerRegistry containerRegistry)
{
    ViewModelLocationProvider.Register<ViewA, ViewAViewModel>();
    ViewModelLocationProvider.Register<ViewA>(() => new ViewAViewModel());
}

Commanding

MyViewModel.cs 
public ICommand DoCommand { get; }
public DelegateCommand<string> DoWithParamCommand { 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

Cs.svg 
private bool isEnabled;

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

ObservesProperty

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

Cs.svg 
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.

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

Task-Based DelegateCommand

Cs.svg 
DoCommand = new DelegateCommand(DoAsync);

async void DoAsync()
{
    await SomeAsyncMethod();
}

Composite command

Parent command to multiple child commands.

Core/Commands/IApplicationCommands.cs 
public interface IApplicationCommands
{
    CompositeCommand SaveAllCommand { get; }
}
Core/Commands/ApplicationCommands.cs 
public class ApplicationCommands : IApplicationCommands
{
    public CompositeCommand SaveAllCommand { get; } = new CompositeCommand();
}
App.xaml.cs 
protected override void RegisterTypes(IContainerRegistry containerRegistry)
{
    containerRegistry.RegisterSingleton<IApplicationCommands, ApplicationCommands>();
}
ViewModels/MainWindowViewModel.cs 
private IApplicationCommands applicationCommands;
public IApplicationCommands ApplicationCommands
{
    get { return applicationCommands; }
    set { SetProperty(ref applicationCommands, value); }
}

public MainWindowViewModel(IApplicationCommands applicationCommands)
{
    ApplicationCommands = applicationCommands;
}
ModuleA/ViewModels/ViewAViewModel.cs 
public DelegateCommand SaveCommand { get; private set; }

public TabViewModel(IApplicationCommands applicationCommands)
{
    SaveCommand = new DelegateCommand(Save).ObservesCanExecute(() => CanSave);
    applicationCommands.SaveAllCommand.RegisterCommand(SaveCommand);
}

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.

Region

  • Region: placeholder for dynamic content where views will be injected.
  • Region manager: maintains a collection of all the regions of the application. Used for:
    • create and define regions
    • access to regions
    • region navigation
    • views composition
Xaml.svg 
<ContentControl prism:RegionManager.RegionName="MyRegion" />
App.xaml.cs 
protected override void OnInitialized()
{
    base.OnInitialized();

    var regionManager = Container.Resolve<IRegionManager>();
    regionManager.RegisterViewWithRegion("MyRegion", typeof(MyView));
}

View discovery

Region looks for view type.

ModuleAModule.cs 
public void OnInitialized(IContainerProvider containerProvider)
{
    this.regionManager.RegisterViewWithRegion("MyRegion", typeof(ViewA));
}

View injection

ModuleAModule.cs 
public void OnInitialized(IContainerProvider containerProvider)
{
    var viewA = containerProvider.Resolve<ViewA>();
    var contentRegion = this.regionManager.Regions["ContentRegion"];
    contentRegion.Add(viewA);

    contentRegion.Add(anotherView);       // add another view to the region
    contentRegion.Activate(anotherView);  // tell the region to display this view

    contentRegion.Deactivate(anotherView);  // tell the region not to display this view anymore
}

Region behavior

Allow to execute some code when a region is adapted.

MyRegionBehavior.cs 
public class DependentViewRegionBehavior : RegionBehavior
{
    protected override void OnAttach()
    { }
}
App.xaml.cs 
protected override void ConfigureDefaultRegionBehaviors(IRegionBehaviorFactory regionBehaviors)
{
    base.ConfigureDefaultRegionBehaviors(regionBehaviors);

    regionBehaviors.AddIfMissing(nameof(MyRegionBehavior), typeof(MyRegionBehavior));
}

Region adapter

  • Adapts a view to a region.

Prism provides 3 region adapters:

  • ContentControlRegionAdapter allow to inject a view in a ContentControl
  • ItemsControlRegionAdapter allow to inject a view in an ItemsControl
  • SelectorRegionAdapter allow to inject a view in a ComboBox ListBox Ribbon TabControl

Other controls require a custom region adapter.

Core/Regions/StackPanelRegionAdapter.cs 
internal sealed class StackPanelRegionAdapter : RegionAdapterBase<StackPanel>
{
    public StackPanelRegionAdapter(RegionBehaviorFactory behaviorFactory)
        : base(behaviorFactory)
    { }

    protected override void Adapt(IRegion region, StackPanel regionTarget)
    {
        region.Views.CollectionChanged += (s, e) =>
        {
            if (e.Action == NotifyCollectionChangedAction.Add)
            {
                foreach (FrameworkElement item in e.NewItems)
                {
                    regionTarget.Children.Add(item);
                }
            }
            else if (e.Action == NotifyCollectionChangedAction.Remove)
            {
                foreach (FrameworkElement item in e.OldItems)
                {
                    regionTarget.Children.Remove(item);
                }
            }
        }; 
    }

    protected override IRegion CreateRegion() => new Region();
}
App.xaml.cs 
protected override void ConfigureRegionAdapterMappings(RegionAdapterMappings regionAdapterMappings)
{
    base.ConfigureRegionAdapterMappings(regionAdapterMappings);

    regionAdapterMappings.RegisterMapping<StackPanel>(Container.Resolve<StackPanelRegionAdapter>());
}

Navigation

Move between views in a region based on url.
By default create a new instance a the view before to navigate to it or reuse the existing one (discriminate by view type) if it has already been created.

ModuleAModule.cs 
public void RegisterTypes(IContainerRegistry containerRegistry)
{
    // register the ViewA under the unique string key ViewA (type of the view by default)
    containerRegistry.RegisterForNavigation<ViewA>();
    containerRegistry.RegisterForNavigation<ViewB>();

    // associate a view-model while register
    containerRegistry.RegisterForNavigation<ViewA, ViewAViewModel>();
}
ViewAViewModel.cs 
internal sealed class ViewAViewModel : BindableBase, INavigationAware
{
    public void OnNavigatedTo(NavigationContext navigationContext)
    {
        var id = navigationContext.Parameters.GetValue<int>("id");
        var key = navigationContext.Parameters.GetValue<string>("key");
    }

    public void OnNavigatedFrom(NavigationContext navigationContext)
    { }

    // true  → reuse the existing instance
    // false → create a new instance 
    public bool IsNavigationTarget(NavigationContext navigationContext) => true;
}
Views/MainWindow.xaml 
<Button Command="{Binding NavigateCommand}"
        CommandParameter="ViewA"
        Content="Navigate to A" />
<Button Command="{Binding NavigateCommand}"
        CommandParameter="ViewB  "
        Content="Navigate to B" />
ViewModels/MainWindowViewModel.cs 
private readonly IRegionManager regionManager;

public DelegateCommand<string> NavigateCommand { get; private set; }

public MainWindowViewModel(IRegionManager regionManager)
{
    this.regionManager = regionManager;
    this.NavigateCommand = new DelegateCommand<string>(Navigate);
}

private void Navigate(string uri)
{
    var navigationParameters = new NavigationParameters();
    navigationParameters.Add("key", "value");

    this.regionManager.RequestNavigate("ContentRegion", $"{uri}?id=1", navigationParameters);
}

Confirm navigation request

ViewAViewModel.cs 
internal sealed class ViewAViewModel : BindableBase, IConfirmNavigationRequest
{
    public void ConfirmNavigationRequest(NavigationContext navigationContext, Action<bool> continuationCallBack)
    {
        var continueNavigation = true;
        continuationCallBack(continueNavigation);
    }
}

Navigation journal

ViewAViewModel.cs 
internal sealed class ViewAViewModel : BindableBase, INavigationAware
{
    private IRegionNavigationJournal journal;

    public DelegateCommand GoBackCommand { get; set; }

    public ViewAViewModel()
    {
        GoBackCommand = new DelegateCommand(GoBack);
    }

    public void OnNavigatedTo(NavigationContext navigationContext)
    {
        journal = navigationContext.NavigationService.Journal;
    }

    private void GoBack() => journal.GoBack();
}

Navigation with TabControl

Modules

A module represents a functional responsability of the application (independent feature).

  1. Add → New Project → WPF UserControl Library
  2. Remove AssemblyInfo.cs and UserControl1.xaml
  3. Add Prism.Wpf Nuget package
ModuleAModule.cs 
public sealed class ModuleAModule : IModule
{
    public void OnInitialized(IContainerProvider containerProvider)
    { }

    public void RegisterTypes(IContainerRegistry containerRegistry)
    { }
}

Module catalog

Collection of modules that the application is going to load.

Code base

Hard reference to the modules.

App.xaml.cs 
protected override void ConfigureModuleCatalog(IModuleCatalog moduleCatalog)
{
    moduleCatalog.AddModule<ModuleAModule>();
}

App.config

More loosely coupled approach.

App.xaml.cs 
protected override IModuleCatalog CreateModuleCatalog()
    => new ConfigurationModuleCatalog();
App.config 
<configuration>
  <configSections>
    <section name="modules"
             type="Prism.Modularity.ModulesConfigurationSection, Prism.Wpf" />
  </configSections>

  <modules>
    <module assemblyFile="ModuleA.dll"
            moduleType="ModuleA.ModileAModule, ModuleA, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"
            moduleName="ModuleAModule"
            startupLoaded="True" />
  </modules>
</configuration>
Dos.svg 
REM ModuleA post build event
xcopy /y "$(TargetDir)*.*" "$(SolutionDir)$(SolutionName)\$(OutDir)"

Directory

Define a location on disk where to find the modules.

App.xaml.cs 
protected override IModuleCatalog CreateModuleCatalog()
    => new DirectoryModuleCatalog() { ModulePath = @".\Modules" };
Dos.svg 
REM ModuleA post build event
xcopy /y "$(TargetDir)$(TargetName)$(TargetExt)" "$(SolutionDir)$(SolutionName)\$(OutDir)Modules\"
REM xcopy /y C:\PrismNetCore\ModuleA\bin\Debug\net5.0-windows\ModuleA.dll C:\PrismNetCore\PrismNetCore\bin\Debug\net5.0-windows\Modules\

XAML resource dictionary

Event Aggregator

Loosely coupled event-based communication.
Event mechanism that enables communications between loosely coupled components in the application.

MyApp.Core/MyPayload.cs 
public sealed class MyPayload
{
    public string Prop1 { get; set; }
    public string Prop2 { get; set; }
}
MyApp.Core/MyEvent.cs 
public sealed class MyEvent : PubSubEvent<MyPayload>
{ }
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<MyEvent>().Publish(payload);

    // subscribing to events
    eventAggregator.GetEvent<MyEvent>().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.

Cs.svg 
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

Cs.svg 
eventAggregator.GetEvent<MyEvent>().Subscribe(MyAction, ThreadOption.PublisherThread, false, x => x.Prop1 == "KeyMessage");

Performance concern

Cs.svg 
var keepSubscriberReferenceAlive = true;
var myEvent = eventAggregator.GetEvent<MyEvent>();

myEvent.Subscribe(MyAction, keepSubscriberReferenceAlive);
myEvent.Unsubscribe(MyAction);

SubscriptionToken token = myEvent.Subscribe(MyAction, keepSubscriberReferenceAlive);
myEvent.Unsubscribe(token);
keepSubscriberReferenceAlive
true the event instance keeps a strong reference to the subscriber instance, thereby not allowing it to get garbage collected.
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.

Dialog

Popup window displayed over the current application.

ViewModels/ViewAViewModel.cs 
private readonly IDialogService dialogService;

public DelegateCommand OpenDialogCommand { get; private set; }

public ViewAViewModel(IDialogService dialogService)
{
    this.dialogService = dialogService;
    this.OpenDialogCommand = new DelegateCommand(OpenDialog);
}

private void OpenDialog()
{
    var dialogParameters = new DialogParameters();
    dialogParameters.Add("message", "Dialog message !");

    // MessageDialog: same name as the view
    this.dialogService.ShowDialog("MessageDialog", dialogParameters, (dialogResult) =>
    {
        var buttonResult = dialogResult.Result;
        var value = dialogResult.Parameters.GetValue<string>("key");
    });
}
Dialogs/MessageDialog.xaml 
<UserControl x:Class="ModuleA.Dialogs.MessageDialog"
             xmlns:mvvm="http://prismlibrary.com/"
             d:DataContext="{d:DesignInstance dialogs:MessageDialogViewModel}"
             mvvm:ViewModelLocator.AutoWireViewModel="True"
             mc:Ignorable="d">

    <prism:Dialog.WindowStyle>
        <Style TargetType="Window">
            <Setter Property="Height" Value="200" />
            <Setter Property="Width" Value="400" />
            <Setter Property="ResizeMode" Value="NoResize" />
            <Setter Property="prism:Dialog.WindowStartupLocation" Value="CenterOwner" />
        </Style>
    </prism:Dialog.WindowStyle>

    <DockPanel>
        <Button Command="{Binding CloseDialogCommand}"
                Content="Ok"
                DockPanel.Dock="Bottom" />
        <TextBlock Text="{Binding Message}" />
    </DockPanel>
</UserControl>
Dialogs/MessageDialogViewModel 
internal sealed class MessageDialogViewModel : BindableBase, IDialogAware
{
    public string Title => "Dialog message";
    public event Action<IDialogResult> RequestClose;
    public ICommand CloseDialogCommand { get; }

    private string message;
    public string Message
    {
        get => message;
        set => SetProperty(ref message, value);
    }

    public MessageDialogViewModel()
    {
        CloseDialogCommand = new DelegateCommand(CloseDialog, CanCloseDialog);
    }

    public bool CanCloseDialog() => true;

    public void OnDialogClosed()
    { }

    public void OnDialogOpened(IDialogParameters parameters)
    {
        Message = parameters.GetValue<string>("message");
    }

    private void CloseDialog()
    {
        var dialogParameters = new DialogParameters
        {
            { "key", "value" }
        };
        this.RequestClose?.Invoke(new DialogResult(ButtonResult.OK, dialogParameters));
    }
}
ModuleAModule.cs 
public void RegisterTypes(IContainerRegistry containerRegistry)
{
    // register the MessageDialog under the unique string key MessageDialog (type of the dialog by default)
    containerRegistry.RegisterDialog<MessageDialog>(); 
}
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