回答編集履歴

  なんか堂々巡りですね^^;

  どうもprismユーザーと話が合わないのは、私がわかってないだけなんでしょうか？（だったらいいのですが^^;

 

  理屈上は`RelativeSource`で`Window`とでもすれば引っ張ってこれますが、そんなのイヤすぎますよね？

 

  そもそもガッツリprismしている場合、`UserControl`の表示は↓のようになりませんか？（Prism Full App(.NET Core)テンプレートより）

  <ContentControl prism:RegionManager.RegionName="{x:Static core:RegionNames.ContentRegion}" />

  `DependencyProperty`を設定するタイミングもないです（まあやりようはあるんでしょうけど）

 

  一度Prism Full App(.NET Core)テンプレートを作っていただいて、`ViewA`・`ViewAViewModel`・`MessageService`の関係を見ていただけたらいいと思います。

 

  ---

 

  例がないと話の前提が合いませんので雑に作りました（`Func<T,R>`が気持ち悪いのは気にしないでください^^;

  [NuGet Gallery | Prism.DryIoc 8.1.97](https://www.nuget.org/packages/Prism.DryIoc/8.1.97)

  [NuGet Gallery | ReactiveProperty 7.12.0](https://www.nuget.org/packages/ReactiveProperty/7.12.0)

 

  `TextBox`と`TextBlock`の組が４つあります。どれも動作は同じです（入力値の小文字が大文字になって表示される）

 

  ４つのうち１つだけおかしい（異質な）ものがあります。

 

  <Window

  x:Class="Questions362091.Views.MainWindow"

  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

  xmlns:prism="http://prismlibrary.com/"

  xmlns:views="clr-namespace:Questions362091.Views"

  Width="525"

  SizeToContent="Height">

 

  <GroupBox Header="ベタ置き">

  <StackPanel>

  <TextBox Text="{Binding Input.Value, UpdateSourceTrigger=PropertyChanged}" />

  <TextBlock HorizontalAlignment="Center" Text="↓" />

  <TextBlock Text="{Binding Output.Value}" />

  </StackPanel>

 

  <GroupBox Header="UserControl1">

  <views:UserControl1 />

 

  <GroupBox Header="PrismUserControl1">

  <ContentControl prism:RegionManager.RegionName="ContentRegion" />

 

  <GroupBox Header="UserControl2">

  <views:UserControl2 Converter="{Binding Converter}" Input="{Binding Input.Value}" />

  </Window>

  <UserControl

  x:Class="Questions362091.Views.UserControl1"

  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

  <TextBox Text="{Binding Input.Value, UpdateSourceTrigger=PropertyChanged}" />

  <TextBlock HorizontalAlignment="Center" Text="↓" />

  <TextBlock Text="{Binding Output.Value}" />

  </UserControl>

  <UserControl

  x:Class="Questions362091.Views.PrismUserControl1"

  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

  <TextBox Text="{Binding Input.Value, UpdateSourceTrigger=PropertyChanged}" />

  <TextBlock HorizontalAlignment="Center" Text="↓" />

  <TextBlock Text="{Binding Output.Value}" />

  </UserControl>

  <UserControl

  x:Class="Questions362091.Views.UserControl2"

  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

  xmlns:views="clr-namespace:Questions362091.Views">

  <TextBox Text="{Binding Input, UpdateSourceTrigger=PropertyChanged, RelativeSource={RelativeSource AncestorType={x:Type views:UserControl2}}}" />

  <TextBlock HorizontalAlignment="Center" Text="↓" />

  <TextBlock Text="{Binding Output, RelativeSource={RelativeSource AncestorType={x:Type views:UserControl2}}}" />

  </UserControl>

  using System;

  using System.Windows;

  using System.Windows.Controls;

 

  namespace Questions362091.Views

  public partial class UserControl2 : UserControl

  public string Input { get => (string)GetValue(InputProperty); set => SetValue(InputProperty, value); }

  public static readonly DependencyProperty InputProperty = DependencyProperty.Register(nameof(Input), typeof(string), typeof(UserControl2), new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, InputChanged));

  private static void InputChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)

  if (d is UserControl2 userControl2)

  userControl2.Output = userControl2.Converter?.Invoke((string)e.NewValue);

 

  public string Output { get => (string)GetValue(OutputProperty); protected set => SetValue(OutputPropertyKey, value); }

  private static readonly DependencyPropertyKey OutputPropertyKey = DependencyProperty.RegisterReadOnly(nameof(Output), typeof(string), typeof(UserControl2), new());

  public static readonly DependencyProperty OutputProperty = OutputPropertyKey.DependencyProperty;

 

  public Func<string, string> Converter { get => (Func<string, string>)GetValue(ConverterProperty); set => SetValue(ConverterProperty, value); }

  public static readonly DependencyProperty ConverterProperty = DependencyProperty.Register(nameof(Converter), typeof(Func<string, string>), typeof(UserControl2), new((Func<string, string>)(s => s)));

 

  public UserControl2() => InitializeComponent();

  using Prism.Mvvm;

  using Prism.Regions;

  using Questions362091.Models;

  using Reactive.Bindings;

  using Reactive.Bindings.Extensions;

  using System;

 

  namespace Questions362091.ViewModels

  public class MainWindowViewModel : BindableBase

  public ReactiveProperty<string> Input { get; }

  public ReadOnlyReactiveProperty<string> Output { get; }

  public Func<string, string> Converter => model.Converter;

 

  private readonly Model model;

 

  public MainWindowViewModel(Model model, IRegionManager regionManager)

  this.model = model;

  Input = model.Input.ToReactivePropertyAsSynchronized(x => x.Value);

  Output = model.Output.ToReadOnlyReactiveProperty();

  using Prism.Mvvm;

  using Questions362091.Models;

  using Reactive.Bindings;

  using Reactive.Bindings.Extensions;

 

  namespace Questions362091.ViewModels

  public class PrismUserControl1ViewModel : BindableBase

  public ReactiveProperty<string> Input { get; }

  public ReadOnlyReactiveProperty<string> Output { get; }

 

  public PrismUserControl1ViewModel(Model model)

  Input = model.Input.ToReactivePropertyAsSynchronized(x => x.Value);

  Output = model.Output.ToReadOnlyReactiveProperty();

  using Reactive.Bindings;

  using System;

  using System.Reactive.Linq;

 

  namespace Questions362091.Models

  public class Model

  public ReactivePropertySlim<string> Input { get; } = new();

  public ReadOnlyReactivePropertySlim<string> Output { get; }

  public Func<string, string> Converter { get; } = s => s?.ToUpper();

 

  public Model() => Output = Input.Select(Converter).ToReadOnlyReactivePropertySlim();

  using Prism.Ioc;

  using Prism.Regions;

  using Questions362091.Models;

  using Questions362091.Views;

  using System.Windows;

 

  namespace Questions362091

  public partial class App

  protected override Window CreateShell() => Container.Resolve<MainWindow>();

  protected override void OnInitialized()

  base.OnInitialized();

  var regionManager = Container.Resolve<IRegionManager>();

  regionManager.RegisterViewWithRegion("ContentRegion", typeof(PrismUserControl1));

  protected override void RegisterTypes(IContainerRegistry containerRegistry)

  containerRegistry.RegisterSingleton<Model>();

  containerRegistry.RegisterForNavigation<PrismUserControl1>();