Add NotifyPropertyChangedExtensions (WatchProperty, WatchProperties, WatchAllProperties)

PowerKit.Tests/Extensions/NotifyPropertyChangedExtensionsTests.cs

@@ -0,0 +1,105 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+using FluentAssertions;
+using PowerKit.Extensions;
+using Xunit;
+
+namespace PowerKit.Tests.Extensions;
+
+file class FakeNotifyPropertyChanged : INotifyPropertyChanged
+{
+    public event PropertyChangedEventHandler? PropertyChanged;
+
+    public string? StringProperty
+    {
+        get;
+        set
+        {
+            field = value;
+            OnPropertyChanged();
+        }
+    }
+
+    public int IntProperty
+    {
+        get;
+        set
+        {
+            field = value;
+            OnPropertyChanged();
+        }
+    }
+
+    public void RaiseAllPropertiesChanged() =>
+        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(string.Empty));
+
+    private void OnPropertyChanged([CallerMemberName] string? propertyName = null) =>
+        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+}
+
+public class NotifyPropertyChangedExtensionsTests
+{
+    [Fact]
+    public void WatchProperty_Test()
+    {
+        // Arrange
+        var obj = new FakeNotifyPropertyChanged { StringProperty = "initial" };
+        var values = new List<string?>();
+
+        // Act
+        var sub = obj.WatchProperty(x => x.StringProperty, v => values.Add(v), true);
+
+        obj.StringProperty = "hello";
+        obj.IntProperty = 42;
+        obj.RaiseAllPropertiesChanged();
+        sub.Dispose();
+        obj.StringProperty = "world";
+
+        // Assert
+        values.Should().Equal("initial", "hello", "hello");
+    }
+
+    [Fact]
+    public void WatchProperties_Test()
+    {
+        // Arrange
+        var obj = new FakeNotifyPropertyChanged();
+        var callCount = 0;
+
+        // Act
+        var sub = obj.WatchProperties(
+            [x => x.StringProperty, x => x.IntProperty],
+            () => callCount++,
+            true
+        );
+
+        obj.StringProperty = "hello";
+        obj.IntProperty = 42;
+        obj.RaiseAllPropertiesChanged();
+        sub.Dispose();
+        obj.StringProperty = "world";
+
+        // Assert
+        callCount.Should().Be(4);
+    }
+
+    [Fact]
+    public void WatchAllProperties_Test()
+    {
+        // Arrange
+        var obj = new FakeNotifyPropertyChanged();
+        var callCount = 0;
+
+        // Act
+        var sub = obj.WatchAllProperties(() => callCount++, true);
+        obj.StringProperty = "hello";
+        obj.IntProperty = 42;
+        sub.Dispose();
+        obj.StringProperty = "world";
+
+        // Assert
+        callCount.Should().Be(3);
+    }
+}

PowerKit/Extensions/NotifyPropertyChangedExtensions.cs

@@ -0,0 +1,144 @@
+#nullable enable
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Reflection;
+
+namespace PowerKit.Extensions;
+
+#if !POWERKIT_INCLUDE_COVERAGE
+[ExcludeFromCodeCoverage]
+#endif
+internal static class NotifyPropertyChangedExtensions
+{
+    extension<TOwner>(TOwner owner)
+        where TOwner : INotifyPropertyChanged
+    {
+        /// <summary>
+        /// Subscribes to changes of the specified property on the owner object.
+        /// The returned <see cref="IDisposable" /> can be disposed to unsubscribe.
+        /// </summary>
+        public IDisposable WatchProperty<TProperty>(
+            Expression<Func<TOwner, TProperty>> propertyExpression,
+            Action<TProperty> callback,
+            bool watchInitialValue = false
+        )
+        {
+            var memberExpression =
+                propertyExpression.Body as MemberExpression
+                // The compiler implicitly wraps value types in a conversion expression when
+                // the expression is typed to return a reference type.
+                ?? (propertyExpression.Body as UnaryExpression)?.Operand as MemberExpression;
+
+            if (
+                memberExpression?.Member is not PropertyInfo property
+                || !property.DeclaringType!.IsAssignableFrom(typeof(TOwner))
+            )
+            {
+                throw new ArgumentException(
+                    "Provided expression must reference a property of the owner type.",
+                    nameof(propertyExpression)
+                );
+            }
+
+            var getValue = propertyExpression.Compile();
+
+            void OnPropertyChanged(object? sender, PropertyChangedEventArgs args)
+            {
+                if (
+                    string.IsNullOrWhiteSpace(args.PropertyName)
+                    || string.Equals(args.PropertyName, property.Name, StringComparison.Ordinal)
+                )
+                {
+                    callback(getValue(owner));
+                }
+            }
+
+            owner.PropertyChanged += OnPropertyChanged;
+
+            if (watchInitialValue)
+            {
+                callback(getValue(owner));
+            }
+
+            return Disposable.Create(() => owner.PropertyChanged -= OnPropertyChanged);
+        }
+
+        /// <summary>
+        /// Subscribes to changes of the specified properties on the owner object.
+        /// The returned <see cref="IDisposable" /> can be disposed to unsubscribe.
+        /// </summary>
+        public IDisposable WatchProperties(
+            IEnumerable<Expression<Func<TOwner, object?>>> propertyExpressions,
+            Action callback,
+            bool watchInitialValue = false
+        )
+        {
+            var properties = propertyExpressions
+                .Select(expression =>
+                {
+                    var memberExpression =
+                        expression.Body as MemberExpression
+                        // Because the expression is typed to return an object, the compiler will
+                        // implicitly wrap it in a conversion unary expression if it's of any other type.
+                        ?? (expression.Body as UnaryExpression)?.Operand as MemberExpression;
+
+                    if (
+                        memberExpression?.Member is not PropertyInfo property
+                        || !property.DeclaringType!.IsAssignableFrom(typeof(TOwner))
+                    )
+                    {
+                        throw new ArgumentException(
+                            "Provided expression must reference a property of the owner type.",
+                            nameof(propertyExpressions)
+                        );
+                    }
+
+                    return property;
+                })
+                .ToArray();
+
+            void OnPropertyChanged(object? sender, PropertyChangedEventArgs args)
+            {
+                if (
+                    string.IsNullOrWhiteSpace(args.PropertyName)
+                    || properties.Any(p =>
+                        string.Equals(args.PropertyName, p.Name, StringComparison.Ordinal)
+                    )
+                )
+                {
+                    callback();
+                }
+            }
+
+            owner.PropertyChanged += OnPropertyChanged;
+
+            if (watchInitialValue)
+            {
+                callback();
+            }
+
+            return Disposable.Create(() => owner.PropertyChanged -= OnPropertyChanged);
+        }
+
+        /// <summary>
+        /// Subscribes to changes of all properties on the owner object.
+        /// The returned <see cref="IDisposable" /> can be disposed to unsubscribe.
+        /// </summary>
+        public IDisposable WatchAllProperties(Action callback, bool watchInitialValue = false)
+        {
+            void OnPropertyChanged(object? sender, PropertyChangedEventArgs args) => callback();
+            owner.PropertyChanged += OnPropertyChanged;
+
+            if (watchInitialValue)
+            {
+                callback();
+            }
+
+            return Disposable.Create(() => owner.PropertyChanged -= OnPropertyChanged);
+        }
+    }
+}