[Feature] Microsoft.Toolkit.Mvvm package (Preview 4) (#3527)

## Follow up to #3428 
<!-- Add the relevant issue number after the "#" mentioned above (for ex: Fixes #1234) which will automatically close the issue once the PR is merged. -->
This PR is for tracking all changes/fixes/improvements to the `Microsoft.Toolkit.Mvvm` package following the Preview 3.

<!-- Add a brief overview here of the feature/bug & fix. -->

## PR Type
What kind of change does this PR introduce?
<!-- Please uncomment one or more that apply to this PR. -->

- Feature
- Improvements
<!-- - Code style update (formatting) -->
<!-- - Refactoring (no functional changes, no api changes) -->
<!-- - Build or CI related changes -->
<!-- - Documentation content changes -->
<!-- - Sample app changes -->
<!-- - Other... Please describe: -->

## Overview

This PR is used to track and implement new features and tweaks for the `Microsoft.Toolkit.Mvvm` package.
See the linked issue for more info, and for a full list of changes included in this PR.


## PR Checklist

Please check if your PR fulfills the following requirements:

- [X] Tested code with current [supported SDKs](../readme.md#supported)
- [ ] ~~Pull Request has been submitted to the documentation repository [instructions](..\contributing.md#docs). Link: <!-- docs PR link -->~~
- [ ] ~~Sample in sample app has been added / updated (for bug fixes / features)~~
    - [ ] ~~Icon has been created (if new sample) following the [Thumbnail Style Guide and templates](https://github.com/windows-toolkit/WindowsCommunityToolkit-design-assets)~~
- [X] Tests for the changes have been added (for bug fixes / features) (if applicable)
- [X] Header has been added to all new source files (run *build/UpdateHeaders.bat*)
- [X] Contains **NO** breaking changes

Author: msftbot[bot]

Microsoft.Toolkit.Mvvm/ComponentModel/ObservableObject.cs

@@ -27,25 +27,39 @@ public abstract class ObservableObject : INotifyPropertyChanged, INotifyProperty
         public event PropertyChangingEventHandler? PropertyChanging;
 
         /// <summary>
-        /// Performs the required configuration when a property has changed, and then
-        /// raises the <see cref="PropertyChanged"/> event to notify listeners of the update.
+        /// Raises the <see cref="PropertyChanged"/> event.
+        /// </summary>
+        /// <param name="e">The input <see cref="PropertyChangedEventArgs"/> instance.</param>
+        protected virtual void OnPropertyChanged(PropertyChangedEventArgs e)
+        {
+            PropertyChanged?.Invoke(this, e);
+        }
+
+        /// <summary>
+        /// Raises the <see cref="PropertyChanging"/> event.
+        /// </summary>
+        /// <param name="e">The input <see cref="PropertyChangingEventArgs"/> instance.</param>
+        protected virtual void OnPropertyChanging(PropertyChangingEventArgs e)
+        {
+            PropertyChanging?.Invoke(this, e);
+        }
+
+        /// <summary>
+        /// Raises the <see cref="PropertyChanged"/> event.
         /// </summary>
         /// <param name="propertyName">(optional) The name of the property that changed.</param>
-        /// <remarks>The base implementation only raises the <see cref="PropertyChanged"/> event.</remarks>
-        protected virtual void OnPropertyChanged([CallerMemberName] string? propertyName = null)
+        protected void OnPropertyChanged([CallerMemberName] string? propertyName = null)
         {
-            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+            OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
         }
 
         /// <summary>
-        /// Performs the required configuration when a property is changing, and then
-        /// raises the <see cref="PropertyChanged"/> event to notify listeners of the update.
+        /// Raises the <see cref="PropertyChanging"/> event.
         /// </summary>
         /// <param name="propertyName">(optional) The name of the property that changed.</param>
-        /// <remarks>The base implementation only raises the <see cref="PropertyChanging"/> event.</remarks>
-        protected virtual void OnPropertyChanging([CallerMemberName] string? propertyName = null)
+        protected void OnPropertyChanging([CallerMemberName] string? propertyName = null)
         {
-            PropertyChanging?.Invoke(this, new PropertyChangingEventArgs(propertyName));
+            OnPropertyChanging(new PropertyChangingEventArgs(propertyName));
         }
 
         /// <summary>

Microsoft.Toolkit.Mvvm/ComponentModel/ObservableValidator.cs

@@ -0,0 +1,167 @@
+// 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 more information.
+
+using System;
+using System.Threading;
+
+#nullable enable
+
+namespace Microsoft.Toolkit.Mvvm.DependencyInjection
+{
+    /// <summary>
+    /// A type that facilitates the use of the <see cref="IServiceProvider"/> type.
+    /// The <see cref="Ioc"/> provides the ability to configure services in a singleton, thread-safe
+    /// service provider instance, which can then be used to resolve service instances.
+    /// The first step to use this feature is to declare some services, for instance:
+    /// <code>
+    /// public interface ILogger
+    /// {
+    ///     void Log(string text);
+    /// }
+    /// </code>
+    /// <code>
+    /// public class ConsoleLogger : ILogger
+    /// {
+    ///     void Log(string text) => Console.WriteLine(text);
+    /// }
+    /// </code>
+    /// Then the services configuration should then be done at startup, by calling the <see cref="ConfigureServices"/>
+    /// method and passing an <see cref="IServiceProvider"/> instance with the services to use. That instance can
+    /// be from any library offering dependency injection functionality, such as Microsoft.Extensions.DependencyInjection.
+    /// For instance, using that library, <see cref="ConfigureServices"/> can be used as follows in this example:
+    /// <code>
+    /// Ioc.Default.ConfigureServices(
+    ///     new ServiceCollection()
+    ///     .AddSingleton&lt;ILogger, Logger&gt;()
+    ///     .BuildServiceProvider());
+    /// </code>
+    /// Finally, you can use the <see cref="Ioc"/> instance (which implements <see cref="IServiceProvider"/>)
+    /// to retrieve the service instances from anywhere in your application, by doing as follows:
+    /// <code>
+    /// Ioc.Default.GetService&lt;ILogger&gt;().Log("Hello world!");
+    /// </code>
+    /// </summary>
+    public sealed class Ioc : IServiceProvider
+    {
+        /// <summary>
+        /// Gets the default <see cref="Ioc"/> instance.
+        /// </summary>
+        public static Ioc Default { get; } = new Ioc();
+
+        /// <summary>
+        /// The <see cref="IServiceProvider"/> instance to use, if initialized.
+        /// </summary>
+        private volatile IServiceProvider? serviceProvider;
+
+        /// <inheritdoc/>
+        public object? GetService(Type serviceType)
+        {
+            // As per section I.12.6.6 of the official CLI ECMA-335 spec:
+            // "[...] read and write access to properly aligned memory locations no larger than the native
+            // word size is atomic when all the write accesses to a location are the same size. Atomic writes
+            // shall alter no bits other than those written. Unless explicit layout control is used [...],
+            // data elements no larger than the natural word size [...] shall be properly aligned.
+            // Object references shall be treated as though they are stored in the native word size."
+            // The field being accessed here is of native int size (reference type), and is only ever accessed
+            // directly and atomically by a compare exchange instruction (see below), or here. We can therefore
+            // assume this read is thread safe with respect to accesses to this property or to invocations to one
+            // of the available configuration methods. So we can just read the field directly and make the necessary
+            // check with our local copy, without the need of paying the locking overhead from this get accessor.
+            IServiceProvider? provider = this.serviceProvider;
+
+            if (provider is null)
+            {
+                ThrowInvalidOperationExceptionForMissingInitialization();
+            }
+
+            return provider!.GetService(serviceType);
+        }
+
+        /// <summary>
+        /// Tries to resolve an instance of a specified service type.
+        /// </summary>
+        /// <typeparam name="T">The type of service to resolve.</typeparam>
+        /// <returns>An instance of the specified service, or <see langword="null"/>.</returns>
+        /// <exception cref="InvalidOperationException">Throw if the current <see cref="Ioc"/> instance has not been initialized.</exception>
+        public T? GetService<T>()
+            where T : class
+        {
+            IServiceProvider? provider = this.serviceProvider;
+
+            if (provider is null)
+            {
+                ThrowInvalidOperationExceptionForMissingInitialization();
+            }
+
+            return (T?)provider!.GetService(typeof(T));
+        }
+
+        /// <summary>
+        /// Resolves an instance of a specified service type.
+        /// </summary>
+        /// <typeparam name="T">The type of service to resolve.</typeparam>
+        /// <returns>An instance of the specified service, or <see langword="null"/>.</returns>
+        /// <exception cref="InvalidOperationException">
+        /// Throw if the current <see cref="Ioc"/> instance has not been initialized, or if the
+        /// requested service type was not registered in the service provider currently in use.
+        /// </exception>
+        public T GetRequiredService<T>()
+            where T : class
+        {
+            IServiceProvider? provider = this.serviceProvider;
+
+            if (provider is null)
+            {
+                ThrowInvalidOperationExceptionForMissingInitialization();
+            }
+
+            T? service = (T?)provider!.GetService(typeof(T));
+
+            if (service is null)
+            {
+                ThrowInvalidOperationExceptionForUnregisteredType();
+            }
+
+            return service!;
+        }
+
+        /// <summary>
+        /// Initializes the shared <see cref="IServiceProvider"/> instance.
+        /// </summary>
+        /// <param name="serviceProvider">The input <see cref="IServiceProvider"/> instance to use.</param>
+        public void ConfigureServices(IServiceProvider serviceProvider)
+        {
+            IServiceProvider? oldServices = Interlocked.CompareExchange(ref this.serviceProvider, serviceProvider, null);
+
+            if (!(oldServices is null))
+            {
+                ThrowInvalidOperationExceptionForRepeatedConfiguration();
+            }
+        }
+
+        /// <summary>
+        /// Throws an <see cref="InvalidOperationException"/> when the <see cref="IServiceProvider"/> property is used before initialization.
+        /// </summary>
+        private static void ThrowInvalidOperationExceptionForMissingInitialization()
+        {
+            throw new InvalidOperationException("The service provider has not been configured yet");
+        }
+
+        /// <summary>
+        /// Throws an <see cref="InvalidOperationException"/> when the <see cref="IServiceProvider"/> property is missing a type registration.
+        /// </summary>
+        private static void ThrowInvalidOperationExceptionForUnregisteredType()
+        {
+            throw new InvalidOperationException("The requested service type was not registered");
+        }
+
+        /// <summary>
+        /// Throws an <see cref="InvalidOperationException"/> when a configuration is attempted more than once.
+        /// </summary>
+        private static void ThrowInvalidOperationExceptionForRepeatedConfiguration()
+        {
+            throw new InvalidOperationException("The default service provider has already been configured");
+        }
+    }
+}

Microsoft.Toolkit.Mvvm/DependencyInjection/Ioc.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.ComponentModel;
 using System.Runtime.CompilerServices;
 using System.Threading;
 using System.Threading.Tasks;
@@ -18,6 +19,21 @@ namespace Microsoft.Toolkit.Mvvm.Input
     /// </summary>
     public sealed class AsyncRelayCommand : ObservableObject, IAsyncRelayCommand
     {
+        /// <summary>
+        /// The cached <see cref="PropertyChangedEventArgs"/> for <see cref="CanBeCanceled"/>.
+        /// </summary>
+        internal static readonly PropertyChangedEventArgs CanBeCanceledChangedEventArgs = new PropertyChangedEventArgs(nameof(CanBeCanceled));
+
+        /// <summary>
+        /// The cached <see cref="PropertyChangedEventArgs"/> for <see cref="IsCancellationRequested"/>.
+        /// </summary>
+        internal static readonly PropertyChangedEventArgs IsCancellationRequestedChangedEventArgs = new PropertyChangedEventArgs(nameof(IsCancellationRequested));
+
+        /// <summary>
+        /// The cached <see cref="PropertyChangedEventArgs"/> for <see cref="IsRunning"/>.
+        /// </summary>
+        internal static readonly PropertyChangedEventArgs IsRunningChangedEventArgs = new PropertyChangedEventArgs(nameof(IsRunning));
+
         /// <summary>
         /// The <see cref="Func{TResult}"/> to invoke when <see cref="Execute"/> is used.
         /// </summary>
@@ -91,15 +107,22 @@ public Task? ExecutionTask
             get => this.executionTask;
             private set
             {
-                if (SetPropertyAndNotifyOnCompletion(ref this.executionTask, value, _ => OnPropertyChanged(nameof(IsRunning))))
+                if (SetPropertyAndNotifyOnCompletion(ref this.executionTask, value, _ =>
+                {
+                    // When the task completes
+                    OnPropertyChanged(IsRunningChangedEventArgs);
+                    OnPropertyChanged(CanBeCanceledChangedEventArgs);
+                }))
                 {
-                    OnPropertyChanged(nameof(IsRunning));
+                    // When setting the task
+                    OnPropertyChanged(IsRunningChangedEventArgs);
+                    OnPropertyChanged(CanBeCanceledChangedEventArgs);
                 }
             }
         }
 
         /// <inheritdoc/>
-        public bool CanBeCanceled => !(this.cancelableExecute is null);
+        public bool CanBeCanceled => !(this.cancelableExecute is null) && IsRunning;
 
         /// <inheritdoc/>
         public bool IsCancellationRequested => this.cancellationTokenSource?.IsCancellationRequested == true;
@@ -142,7 +165,7 @@ public Task ExecuteAsync(object? parameter)
 
                 var cancellationTokenSource = this.cancellationTokenSource = new CancellationTokenSource();
 
-                OnPropertyChanged(nameof(IsCancellationRequested));
+                OnPropertyChanged(IsCancellationRequestedChangedEventArgs);
 
                 // Invoke the cancelable command delegate with a new linked token
                 return ExecutionTask = this.cancelableExecute!(cancellationTokenSource.Token);
@@ -156,7 +179,8 @@ public void Cancel()
         {
             this.cancellationTokenSource?.Cancel();
 
-            OnPropertyChanged(nameof(IsCancellationRequested));
+            OnPropertyChanged(IsCancellationRequestedChangedEventArgs);
+            OnPropertyChanged(CanBeCanceledChangedEventArgs);
         }
     }
 }

Microsoft.Toolkit.Mvvm/Input/AsyncRelayCommand.cs

@@ -91,15 +91,22 @@ public Task? ExecutionTask
             get => this.executionTask;
             private set
             {
-                if (SetPropertyAndNotifyOnCompletion(ref this.executionTask, value, _ => OnPropertyChanged(nameof(IsRunning))))
+                if (SetPropertyAndNotifyOnCompletion(ref this.executionTask, value, _ =>
                 {
-                    OnPropertyChanged(nameof(IsRunning));
+                    // When the task completes
+                    OnPropertyChanged(AsyncRelayCommand.IsRunningChangedEventArgs);
+                    OnPropertyChanged(AsyncRelayCommand.CanBeCanceledChangedEventArgs);
+                }))
+                {
+                    // When setting the task
+                    OnPropertyChanged(AsyncRelayCommand.IsRunningChangedEventArgs);
+                    OnPropertyChanged(AsyncRelayCommand.CanBeCanceledChangedEventArgs);
                 }
             }
         }
 
         /// <inheritdoc/>
-        public bool CanBeCanceled => !(this.cancelableExecute is null);
+        public bool CanBeCanceled => !(this.cancelableExecute is null) && IsRunning;
 
         /// <inheritdoc/>
         public bool IsCancellationRequested => this.cancellationTokenSource?.IsCancellationRequested == true;
@@ -163,7 +170,7 @@ public Task ExecuteAsync(T parameter)
 
                 var cancellationTokenSource = this.cancellationTokenSource = new CancellationTokenSource();
 
-                OnPropertyChanged(nameof(IsCancellationRequested));
+                OnPropertyChanged(AsyncRelayCommand.IsCancellationRequestedChangedEventArgs);
 
                 // Invoke the cancelable command delegate with a new linked token
                 return ExecutionTask = this.cancelableExecute!(parameter, cancellationTokenSource.Token);
@@ -183,7 +190,8 @@ public void Cancel()
         {
             this.cancellationTokenSource?.Cancel();
 
-            OnPropertyChanged(nameof(IsCancellationRequested));
+            OnPropertyChanged(AsyncRelayCommand.IsCancellationRequestedChangedEventArgs);
+            OnPropertyChanged(AsyncRelayCommand.CanBeCanceledChangedEventArgs);
         }
     }
 }

Microsoft.Toolkit.Mvvm/Input/AsyncRelayCommand{T}.cs

@@ -27,27 +27,10 @@ public static class IMessengerExtensions
         /// </summary>
         private static class MethodInfos
         {
-            /// <summary>
-            /// Initializes static members of the <see cref="MethodInfos"/> class.
-            /// </summary>
-            static MethodInfos()
-            {
-                RegisterIRecipient = (
-                    from methodInfo in typeof(IMessengerExtensions).GetMethods()
-                    where methodInfo.Name == nameof(Register) &&
-                          methodInfo.IsGenericMethod &&
-                          methodInfo.GetGenericArguments().Length == 2
-                    let parameters = methodInfo.GetParameters()
-                    where parameters.Length == 3 &&
-                          parameters[1].ParameterType.IsGenericType &&
-                          parameters[1].ParameterType.GetGenericTypeDefinition() == typeof(IRecipient<>)
-                    select methodInfo).First();
-            }
-
             /// <summary>
             /// The <see cref="MethodInfo"/> instance associated with <see cref="Register{TMessage,TToken}(IMessenger,IRecipient{TMessage},TToken)"/>.
             /// </summary>
-            public static readonly MethodInfo RegisterIRecipient;
+            public static readonly MethodInfo RegisterIRecipient = new Action<IMessenger, IRecipient<object>, Unit>(Register).Method.GetGenericMethodDefinition();
         }
 
         /// <summary>

Microsoft.Toolkit.Mvvm/Messaging/IMessengerExtensions.cs

@@ -65,19 +65,19 @@ public override bool Equals(object? obj)
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public override int GetHashCode()
         {
-            unchecked
-            {
-                // To combine the two hashes, we can simply use the fast djb2 hash algorithm.
-                // This is not a problem in this case since we already know that the base
-                // RuntimeHelpers.GetHashCode method is providing hashes with a good enough distribution.
-                int hash = RuntimeHelpers.GetHashCode(TMessage);
+            // To combine the two hashes, we can simply use the fast djb2 hash algorithm. Unfortunately we
+            // can't really skip the callvirt here (eg. by using RuntimeHelpers.GetHashCode like in other
+            // cases), as there are some niche cases mentioned above that might break when doing so.
+            // However since this method is not generally used in a hot path (eg. the message broadcasting
+            // only invokes this a handful of times when initially retrieving the target mapping), this
+            // doesn't actually make a noticeable difference despite the minor overhead of the virtual call.
+            int hash = TMessage.GetHashCode();
 
-                hash = (hash << 5) + hash;
+            hash = (hash << 5) + hash;
 
-                hash += RuntimeHelpers.GetHashCode(TToken);
+            hash += TToken.GetHashCode();
 
-                return hash;
-            }
+            return hash;
         }
     }
 }