feature: Add ReactivePage for WPF/UWP (#2078)

src/ReactiveUI.Tests/Platforms/wpf/API/ApiApprovalTests.Wpf.net461.approved.txt

@@ -44,6 +44,14 @@ namespace ReactiveUI
         public PlatformOperations() { }
         public string GetOrientation() { }
     }
+    public abstract class ReactivePage<TViewModel> : System.Windows.Controls.Page, ReactiveUI.IActivatable, ReactiveUI.IViewFor, ReactiveUI.IViewFor<TViewModel>
+        where TViewModel :  class
+    {
+        public static readonly System.Windows.DependencyProperty ViewModelProperty;
+        protected ReactivePage() { }
+        public TViewModel BindingRoot { get; }
+        public TViewModel ViewModel { get; set; }
+    }
     public abstract class ReactiveUserControl<TViewModel> : System.Windows.Controls.UserControl, ReactiveUI.IActivatable, ReactiveUI.IViewFor, ReactiveUI.IViewFor<TViewModel>
         where TViewModel :  class
     {

src/ReactiveUI/Platforms/windows-common/ReactivePage.cs

@@ -0,0 +1,114 @@
+// Copyright (c) 2019 .NET Foundation and Contributors. All rights reserved.
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for full license information.
+
+namespace ReactiveUI
+{
+    using System.Diagnostics.CodeAnalysis;
+#if NETFX_CORE || HAS_UNO
+    using Windows.UI.Xaml;
+    using Windows.UI.Xaml.Controls;
+#else
+    using System.Windows;
+    using System.Windows.Controls;
+#endif
+
+    /// <summary>
+    /// A <see cref="Page"/> that is reactive.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// This class is a <see cref="Page"/> that is also reactive. That is, it implements <see cref="IViewFor{TViewModel}"/>.
+    /// You can extend this class to get an implementation of <see cref="IViewFor{TViewModel}"/> rather than writing one yourself.
+    /// </para>
+    /// <para>
+    /// Note that the XAML for your control must specify the same base class, including the generic argument you provide for your view
+    /// model. To do this, use the <c>TypeArguments</c> attribute as follows:
+    /// <code>
+    /// <![CDATA[
+    /// <rxui:ReactivePage
+    ///         x:Class="Foo.Bar.Views.YourView"
+    ///         x:TypeArguments="vms:YourViewModel"
+    ///         xmlns:rxui="http://reactiveui.net"
+    ///         xmlns:vms="clr-namespace:Foo.Bar.ViewModels"
+    ///         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    ///         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    ///         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    ///         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+    ///         mc:Ignorable="d">
+    ///     <!-- view XAML here -->
+    /// </rxui:ReactivePage>
+    /// ]]>
+    /// </code>
+    /// </para>
+    /// <para>
+    /// Note that UWP projects do not support the <c>TypeArguments</c> attribute. The XAML designer window in WPF projects also does not
+    /// support generic types. To use <see cref="ReactivePage{TViewModel}"/> in XAML documents you need to create a base class
+    /// where you derive from <see cref="ReactivePage{TViewModel}"/> with the type argument filled in.
+    /// <code>
+    /// <![CDATA[
+    /// internal class YourViewBase : ReactivePage<YourViewModel> { /* No code needed here */ }
+    ///
+    /// public partial class YourView : YourViewBase
+    /// {
+    ///     /* Your code */
+    /// }
+    /// ]]>
+    /// </code>
+    /// Then you can use this base class as root in your XAML document.
+    /// <code>
+    /// <![CDATA[
+    /// <views:YourViewBase
+    ///         x:Class="Foo.Bar.Views.YourView"
+    ///         xmlns:rxui="http://reactiveui.net"
+    ///         xmlns:vms="clr-namespace:Foo.Bar.ViewModels"
+    ///         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    ///         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    ///         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    ///         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+    ///         mc:Ignorable="d">
+    ///     <!-- view XAML here -->
+    /// </views:YourViewBase>
+    /// ]]>
+    /// </code>
+    /// </para>
+    /// </remarks>
+    /// <typeparam name="TViewModel">
+    /// The type of the view model backing the view.
+    /// </typeparam>
+    [SuppressMessage("Design", "CA1010:Collections should implement generic interface", Justification = "Deliberate usage")]
+    public abstract class ReactivePage<TViewModel> :
+        Page, IViewFor<TViewModel>
+        where TViewModel : class
+    {
+        /// <summary>
+        /// The view model dependency property.
+        /// </summary>
+        public static readonly DependencyProperty ViewModelProperty =
+            DependencyProperty.Register(
+                "ViewModel",
+                typeof(TViewModel),
+                typeof(ReactivePage<TViewModel>),
+                new PropertyMetadata(null));
+
+        /// <summary>
+        /// Gets the binding root view model.
+        /// </summary>
+        public TViewModel BindingRoot => ViewModel;
+
+        /// <inheritdoc/>
+        public TViewModel ViewModel
+        {
+            get => (TViewModel)GetValue(ViewModelProperty);
+            set => SetValue(ViewModelProperty, value);
+        }
+
+        /// <inheritdoc/>
+        object IViewFor.ViewModel
+        {
+            get => ViewModel;
+            set => ViewModel = (TViewModel)value;
+        }
+    }
+}