Feature Add Wpf Validation Binding

src/ReactiveUI.Tests/Platforms/winforms/DefaultPropertyBindingTests.cs

@@ -134,14 +134,14 @@ public void SmokeTestWinformControls()
         var vm = new FakeWinformViewModel();
         var view = new FakeWinformsView { ViewModel = vm };
 
-        var disp = new CompositeDisposable(new[]
-        {
+        var disp = new CompositeDisposable(
+        [
             view.Bind(vm, x => x.Property1, x => x.Property1.Text),
             view.Bind(vm, x => x.Property2, x => x.Property2.Text),
             view.Bind(vm, x => x.Property3, x => x.Property3.Text),
             view.Bind(vm, x => x.Property4, x => x.Property4.Text),
             view.Bind(vm, x => x.BooleanProperty, x => x.BooleanProperty.Checked),
-        });
+        ]);
 
         vm.Property1 = "FOOO";
         Assert.Equal(vm.Property1, view.Property1.Text);

src/ReactiveUI.Tests/Platforms/wpf/API/WpfApiApprovalTests.Wpf.DotNet6_0.verified.txt

@@ -116,6 +116,12 @@ namespace ReactiveUI
             Bounce = 4,
         }
     }
+    public static class ValidationBindingMixins
+    {
+        public static ReactiveUI.IReactiveBinding<TView, TType> BindWithValidation<TViewModel, TView, TVProp, TType>(this TView view, TViewModel viewModel, System.Linq.Expressions.Expression<System.Func<TViewModel, TType?>> viewModelPropertySelector, System.Linq.Expressions.Expression<System.Func<TView, TVProp>> frameworkElementSelector)
+            where TViewModel :  class
+            where TView :  class, ReactiveUI.IViewFor { }
+    }
     public class ViewModelViewHost : ReactiveUI.TransitioningContentControl, ReactiveUI.IActivatableView, ReactiveUI.IViewFor, Splat.IEnableLogger
     {
         public static readonly System.Windows.DependencyProperty ContractFallbackByPassProperty;
@@ -139,4 +145,4 @@ namespace ReactiveUI.Wpf
         public Registrations() { }
         public void Register(System.Action<System.Func<object>, System.Type> registerFunction) { }
     }
-}
+}

src/ReactiveUI.Tests/Platforms/wpf/API/WpfApiApprovalTests.Wpf.DotNet8_0.verified.txt

@@ -116,6 +116,12 @@ namespace ReactiveUI
             Bounce = 4,
         }
     }
+    public static class ValidationBindingMixins
+    {
+        public static ReactiveUI.IReactiveBinding<TView, TType> BindWithValidation<TViewModel, TView, TVProp, TType>(this TView view, TViewModel viewModel, System.Linq.Expressions.Expression<System.Func<TViewModel, TType?>> viewModelPropertySelector, System.Linq.Expressions.Expression<System.Func<TView, TVProp>> frameworkElementSelector)
+            where TViewModel :  class
+            where TView :  class, ReactiveUI.IViewFor { }
+    }
     public class ViewModelViewHost : ReactiveUI.TransitioningContentControl, ReactiveUI.IActivatableView, ReactiveUI.IViewFor, Splat.IEnableLogger
     {
         public static readonly System.Windows.DependencyProperty ContractFallbackByPassProperty;
@@ -139,4 +145,4 @@ namespace ReactiveUI.Wpf
         public Registrations() { }
         public void Register(System.Action<System.Func<object>, System.Type> registerFunction) { }
     }
-}
+}

src/ReactiveUI.Tests/Platforms/wpf/API/WpfApiApprovalTests.Wpf.Net4_7.verified.txt

@@ -114,6 +114,12 @@ namespace ReactiveUI
             Bounce = 4,
         }
     }
+    public static class ValidationBindingMixins
+    {
+        public static ReactiveUI.IReactiveBinding<TView, TType> BindWithValidation<TViewModel, TView, TVProp, TType>(this TView view, TViewModel viewModel, System.Linq.Expressions.Expression<System.Func<TViewModel, TType?>> viewModelPropertySelector, System.Linq.Expressions.Expression<System.Func<TView, TVProp>> frameworkElementSelector)
+            where TViewModel :  class
+            where TView :  class, ReactiveUI.IViewFor { }
+    }
     public class ViewModelViewHost : ReactiveUI.TransitioningContentControl, ReactiveUI.IActivatableView, ReactiveUI.IViewFor, Splat.IEnableLogger
     {
         public static readonly System.Windows.DependencyProperty ContractFallbackByPassProperty;
@@ -137,4 +143,4 @@ namespace ReactiveUI.Wpf
         public Registrations() { }
         public void Register(System.Action<System.Func<object>, System.Type> registerFunction) { }
     }
-}
+}

src/ReactiveUI.Wpf/Binding/ValidationBindingMixins.cs

@@ -0,0 +1,48 @@
+// Copyright (c) 2024 .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.
+
+using System.Linq.Expressions;
+using System.Windows;
+using ReactiveUI.Wpf.Binding;
+
+namespace ReactiveUI;
+
+/// <summary>
+/// ValidationBindingMixins.
+/// </summary>
+public static class ValidationBindingMixins
+{
+    /// <summary>
+    /// Binds the validation.
+    /// </summary>
+    /// <typeparam name="TViewModel">The type of the view model.</typeparam>
+    /// <typeparam name="TView">The type of the view.</typeparam>
+    /// <typeparam name="TVProp">The type of the v property.</typeparam>
+    /// <typeparam name="TType">The type of the type.</typeparam>
+    /// <param name="view">The view.</param>
+    /// <param name="viewModel">The view model.</param>
+    /// <param name="viewModelPropertySelector">The view model property selector.</param>
+    /// <param name="frameworkElementSelector">The framework element selector.</param>
+    /// <returns>
+    /// An instance of <see cref="IDisposable"/> that, when disposed,
+    /// disconnects the binding.
+    /// </returns>
+    public static IReactiveBinding<TView, TType> BindWithValidation<TViewModel, TView, TVProp, TType>(this TView view, TViewModel viewModel, Expression<Func<TViewModel, TType?>> viewModelPropertySelector, Expression<Func<TView, TVProp>> frameworkElementSelector)
+        where TView : class, IViewFor
+        where TViewModel : class
+    {
+        if (viewModelPropertySelector == null)
+        {
+            throw new ArgumentNullException(nameof(viewModelPropertySelector));
+        }
+
+        if (frameworkElementSelector == null)
+        {
+            throw new ArgumentNullException(nameof(frameworkElementSelector));
+        }
+
+        return new ValidationBindingWpf<TView, TViewModel, TVProp, TType>(view, viewModel, viewModelPropertySelector, frameworkElementSelector);
+    }
+}

src/ReactiveUI.Wpf/Binding/ValidationBindingWpf.cs

@@ -0,0 +1,167 @@
+// Copyright (c) 2024 .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.
+
+using System.Linq.Expressions;
+using System.Text;
+using System.Windows;
+using System.Windows.Data;
+using System.Windows.Markup.Primitives;
+using System.Windows.Media;
+using DynamicData;
+
+namespace ReactiveUI.Wpf.Binding;
+
+internal class ValidationBindingWpf<TView, TViewModel, TVProp, TVMProp> : IReactiveBinding<TView, TVMProp>
+    where TView : class, IViewFor
+    where TViewModel : class
+{
+    private const string DotValue = ".";
+    private readonly FrameworkElement _control;
+    private readonly DependencyProperty? _dpPropertyName;
+    private readonly TViewModel _viewModel;
+    private readonly string? _vmPropertyName;
+    private IDisposable? _inner;
+
+    public ValidationBindingWpf(
+        TView view,
+        TViewModel viewModel,
+        Expression<Func<TViewModel, TVMProp?>> vmProperty,
+        Expression<Func<TView, TVProp>> viewProperty)
+    {
+        // Get the ViewModel details
+        _viewModel = viewModel;
+        ViewModelExpression = Reflection.Rewrite(vmProperty.Body);
+        var vmet = ViewModelExpression.GetExpressionChain();
+        var vmFullName = vmet.Select(x => x.GetMemberInfo()?.Name).Aggregate(new StringBuilder(), (sb, x) => sb.Append(x).Append('.')).ToString();
+        if (vmFullName.EndsWith(DotValue))
+        {
+            vmFullName = vmFullName.Substring(0, vmFullName.Length - 1);
+        }
+
+        _vmPropertyName = vmFullName;
+
+        // Get the View details
+        View = view;
+        ViewExpression = Reflection.Rewrite(viewProperty.Body);
+        var vet = ViewExpression.GetExpressionChain().ToArray();
+        var controlName = string.Empty;
+        var index = vet.IndexOf(vet.Last()!);
+        if (vet != null && index > 0)
+        {
+            controlName = vet[vet.IndexOf(vet.Last()!) - 1]!.GetMemberInfo()?.Name
+                ?? throw new ArgumentException($"Control name not found on {typeof(TView).Name}");
+        }
+
+        _control = FindControlsByName(view as DependencyObject, controlName).FirstOrDefault()!;
+        var controlDpPropertyName = vet?.Last().GetMemberInfo()?.Name;
+        _dpPropertyName = GetDependencyProperty(_control, controlDpPropertyName) ?? throw new ArgumentException($"Dependency property not found on {typeof(TVProp).Name}");
+
+        var somethingChanged = Reflection.ViewModelWhenAnyValue(viewModel, view, ViewModelExpression).Select(tvm => (TVMProp?)tvm).Merge(
+              view.WhenAnyDynamic(ViewExpression, x => (TVProp?)x.Value).Select(p => default(TVMProp)));
+        Changed = somethingChanged;
+        Direction = BindingDirection.TwoWay;
+        Bind();
+    }
+
+    public System.Linq.Expressions.Expression ViewModelExpression { get; }
+
+    public TView View { get; }
+
+    public System.Linq.Expressions.Expression ViewExpression { get; }
+
+    public IObservable<TVMProp?> Changed { get; }
+
+    public BindingDirection Direction { get; }
+
+    public IDisposable Bind()
+    {
+        _control.SetBinding(_dpPropertyName, new System.Windows.Data.Binding()
+        {
+            Source = _viewModel,
+            Path = new(_vmPropertyName),
+            Mode = BindingMode.TwoWay,
+            UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged,
+        });
+
+        _inner = Disposable.Create(() => BindingOperations.ClearBinding(_control, _dpPropertyName));
+
+        return _inner;
+    }
+
+    public void Dispose()
+    {
+        _inner?.Dispose();
+        GC.SuppressFinalize(this);
+    }
+
+    private static IEnumerable<DependencyProperty> EnumerateDependencyProperties(object element)
+    {
+        if (element != null)
+        {
+            var markupObject = MarkupWriter.GetMarkupObjectFor(element);
+            if (markupObject != null)
+            {
+                foreach (var mp in markupObject.Properties)
+                {
+                    if (mp.DependencyProperty != null)
+                    {
+                        yield return mp.DependencyProperty;
+                    }
+                }
+            }
+        }
+    }
+
+    private static IEnumerable<DependencyProperty> EnumerateAttachedProperties(object element)
+    {
+        if (element != null)
+        {
+            var markupObject = MarkupWriter.GetMarkupObjectFor(element);
+            if (markupObject != null)
+            {
+                foreach (var mp in markupObject.Properties)
+                {
+                    if (mp.IsAttached)
+                    {
+                        yield return mp.DependencyProperty;
+                    }
+                }
+            }
+        }
+    }
+
+    private static DependencyProperty? GetDependencyProperty(object element, string? name) =>
+        EnumerateDependencyProperties(element).Concat(EnumerateAttachedProperties(element)).FirstOrDefault(x => x.Name == name);
+
+    private static IEnumerable<FrameworkElement> FindControlsByName(DependencyObject? parent, string? name)
+    {
+        if (parent == null)
+        {
+            yield break;
+        }
+
+        if (name == null)
+        {
+            yield break;
+        }
+
+        var childCount = VisualTreeHelper.GetChildrenCount(parent);
+
+        for (var i = 0; i < childCount; i++)
+        {
+            var child = VisualTreeHelper.GetChild(parent, i);
+
+            if (child is FrameworkElement element && element.Name == name)
+            {
+                yield return element;
+            }
+
+            foreach (var descendant in FindControlsByName(child, name))
+            {
+                yield return descendant;
+            }
+        }
+    }
+}