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Merge pull request #461 from CommunityToolkit/dev/messenger-observable
Add IObservable<T> extensions for IMessenger
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‎CommunityToolkit.Mvvm/Messaging/IMessengerExtensions.Observables.cs

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// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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// See the LICENSE file in the project root for more information.
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using System;
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using System.Diagnostics.CodeAnalysis;
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using System.Linq;
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using System.Linq.Expressions;
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using System.Reflection;
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using System.Runtime.CompilerServices;
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using CommunityToolkit.Mvvm.Messaging.Internals;
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namespace CommunityToolkit.Mvvm.Messaging;
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/// <inheritdoc/>
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partial class IMessengerExtensions
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{
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/// <summary>
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/// Creates an <see cref="IObservable{T}"/> instance that can be used to be notified whenever a message of a given type is broadcast by a messenger.
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/// </summary>
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/// <typeparam name="TMessage">The type of message to use to receive notification for through the resulting <see cref="IObservable{T}"/> instance.</typeparam>
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/// <param name="messenger">The <see cref="IMessenger"/> instance to use to register the recipient.</param>
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/// <returns>An <see cref="IObservable{T}"/> instance to receive notifications for <typeparamref name="TMessage"/> messages being broadcast.</returns>
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/// <exception cref="System.ArgumentNullException">Thrown if <paramref name="messenger"/> is <see langword="null"/>.</exception>
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public static IObservable<TMessage> CreateObservable<TMessage>(this IMessenger messenger)
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where TMessage : class
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{
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ArgumentNullException.ThrowIfNull(messenger);
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return new Observable<TMessage>(messenger);
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}
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/// <summary>
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/// Creates an <see cref="IObservable{T}"/> instance that can be used to be notified whenever a message of a given type is broadcast by a messenger.
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/// </summary>
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/// <typeparam name="TMessage">The type of message to use to receive notification for through the resulting <see cref="IObservable{T}"/> instance.</typeparam>
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/// <typeparam name="TToken">The type of token to identify what channel to use to receive messages.</typeparam>
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/// <param name="messenger">The <see cref="IMessenger"/> instance to use to register the recipient.</param>
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/// <param name="token">A token used to determine the receiving channel to use.</param>
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/// <returns>An <see cref="IObservable{T}"/> instance to receive notifications for <typeparamref name="TMessage"/> messages being broadcast.</returns>
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/// <exception cref="System.ArgumentNullException">Thrown if <paramref name="messenger"/> or <paramref name="token"/> are <see langword="null"/>.</exception>
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public static IObservable<TMessage> CreateObservable<TMessage, TToken>(this IMessenger messenger, TToken token)
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where TMessage : class
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where TToken : IEquatable<TToken>
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{
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ArgumentNullException.ThrowIfNull(messenger);
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ArgumentNullException.For<TToken>.ThrowIfNull(token);
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return new Observable<TMessage, TToken>(messenger, token);
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}
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/// <summary>
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/// An <see cref="IObservable{T}"/> implementations for a given message type.
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/// </summary>
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/// <typeparam name="TMessage">The type of messages to listen to.</typeparam>
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private sealed class Observable<TMessage> : IObservable<TMessage>
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where TMessage : class
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{
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/// <summary>
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/// The <see cref="IMessenger"/> instance to use to register the recipient.
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/// </summary>
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private readonly IMessenger messenger;
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/// <summary>
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/// Creates a new <see cref="Observable{TMessage}"/> instance with the given parameters.
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/// </summary>
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/// <param name="messenger">The <see cref="IMessenger"/> instance to use to register the recipient.</param>
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public Observable(IMessenger messenger)
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{
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this.messenger = messenger;
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}
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/// <inheritdoc/>
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public IDisposable Subscribe(IObserver<TMessage> observer)
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{
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return new Recipient(this.messenger, observer);
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}
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/// <summary>
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/// An <see cref="IRecipient{TMessage}"/> implementation for <see cref="Observable{TMessage}"/>.
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/// </summary>
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private sealed class Recipient : IRecipient<TMessage>, IDisposable
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{
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/// <summary>
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/// The <see cref="IMessenger"/> instance to use to register the recipient.
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/// </summary>
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private readonly IMessenger messenger;
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/// <summary>
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/// The target <see cref="IObserver{T}"/> instance currently in use.
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/// </summary>
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private readonly IObserver<TMessage> observer;
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/// <summary>
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/// Creates a new <see cref="Recipient"/> instance with the specified parameters.
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/// </summary>
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/// <param name="messenger">The <see cref="IMessenger"/> instance to use to register the recipient.</param>
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/// <param name="observer">The <see cref="IObserver{T}"/> instance to use to create the recipient for.</param>
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public Recipient(IMessenger messenger, IObserver<TMessage> observer)
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{
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this.messenger = messenger;
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this.observer = observer;
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messenger.Register(this);
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}
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/// <inheritdoc/>
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public void Receive(TMessage message)
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{
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this.observer.OnNext(message);
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}
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/// <inheritdoc/>
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public void Dispose()
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{
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this.messenger.Unregister<TMessage>(this);
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}
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}
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}
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/// <summary>
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/// An <see cref="IObservable{T}"/> implementations for a given pair of message and token types.
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/// </summary>
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/// <typeparam name="TMessage">The type of messages to listen to.</typeparam>
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/// <typeparam name="TToken">The type of token to identify what channel to use to receive messages.</typeparam>
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private sealed class Observable<TMessage, TToken> : IObservable<TMessage>
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where TMessage : class
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where TToken : IEquatable<TToken>
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{
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/// <summary>
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/// The <see cref="IMessenger"/> instance to use to register the recipient.
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/// </summary>
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private readonly IMessenger messenger;
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/// <summary>
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/// The token used to determine the receiving channel to use.
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/// </summary>
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private readonly TToken token;
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/// <summary>
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/// Creates a new <see cref="Observable{TMessage, TToken}"/> instance with the given parameters.
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/// </summary>
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/// <param name="messenger">The <see cref="IMessenger"/> instance to use to register the recipient.</param>
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/// <param name="token">A token used to determine the receiving channel to use.</param>
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public Observable(IMessenger messenger, TToken token)
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{
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this.messenger = messenger;
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this.token = token;
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}
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/// <inheritdoc/>
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public IDisposable Subscribe(IObserver<TMessage> observer)
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{
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return new Recipient(this.messenger, observer, this.token);
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}
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/// <summary>
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/// An <see cref="IRecipient{TMessage}"/> implementation for <see cref="Observable{TMessage, TToken}"/>.
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/// </summary>
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private sealed class Recipient : IRecipient<TMessage>, IDisposable
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{
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/// <summary>
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/// The <see cref="IMessenger"/> instance to use to register the recipient.
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/// </summary>
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private readonly IMessenger messenger;
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/// <summary>
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/// The target <see cref="IObserver{T}"/> instance currently in use.
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/// </summary>
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private readonly IObserver<TMessage> observer;
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/// <summary>
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/// The token used to determine the receiving channel to use.
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/// </summary>
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private readonly TToken token;
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/// <summary>
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/// Creates a new <see cref="Recipient"/> instance with the specified parameters.
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/// </summary>
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/// <param name="messenger">The <see cref="IMessenger"/> instance to use to register the recipient.</param>
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/// <param name="observer">The <see cref="IObserver{T}"/> instance to use to create the recipient for.</param>
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/// <param name="token">A token used to determine the receiving channel to use.</param>
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public Recipient(IMessenger messenger, IObserver<TMessage> observer, TToken token)
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{
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this.messenger = messenger;
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this.observer = observer;
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this.token = token;
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messenger.Register(this, token);
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}
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/// <inheritdoc/>
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public void Receive(TMessage message)
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{
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this.observer.OnNext(message);
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}
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/// <inheritdoc/>
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public void Dispose()
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{
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this.messenger.Unregister<TMessage, TToken>(this, this.token);
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}
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}
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}
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}

‎CommunityToolkit.Mvvm/Messaging/IMessengerExtensions.cs

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/// <summary>
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/// Extensions for the <see cref="IMessenger"/> type.
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/// </summary>
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public static class IMessengerExtensions
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public static partial class IMessengerExtensions
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{
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/// <summary>
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/// A class that acts as a container to load the <see cref="MethodInfo"/> instance linked to

‎tests/CommunityToolkit.Mvvm.Roslyn401.UnitTests/CommunityToolkit.Mvvm.Roslyn401.UnitTests.csproj

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<PackageReference Include="MSTest.TestAdapter" Version="2.2.10" />
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<PackageReference Include="MSTest.TestFramework" Version="2.2.10" />
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<PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.3.2" />
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<PackageReference Include="System.Reactive" Version="5.0.0" />
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<PackageReference Include="System.Text.Json" Version="6.0.6" />
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</ItemGroup>
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‎tests/CommunityToolkit.Mvvm.Roslyn431.UnitTests/CommunityToolkit.Mvvm.Roslyn431.UnitTests.csproj

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<PackageReference Include="MSTest.TestAdapter" Version="2.2.10" />
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<PackageReference Include="MSTest.TestFramework" Version="2.2.10" />
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<PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.3.2" />
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<PackageReference Include="System.Reactive" Version="5.0.0" />
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<PackageReference Include="System.Text.Json" Version="6.0.6" />
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</ItemGroup>
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‎tests/CommunityToolkit.Mvvm.UnitTests/CommunityToolkit.Mvvm.UnitTests.projitems

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<Compile Include="$(MSBuildThisFileDirectory)Test_AsyncRelayCommand{T}.cs" />
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<Compile Include="$(MSBuildThisFileDirectory)Test_INotifyPropertyChangedAttribute.cs" />
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<Compile Include="$(MSBuildThisFileDirectory)Test_IRecipientGenerator.cs" />
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<Compile Include="$(MSBuildThisFileDirectory)Test_Messenger.Observables.cs" />
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<Compile Include="$(MSBuildThisFileDirectory)Test_Messenger.cs" />
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<Compile Include="$(MSBuildThisFileDirectory)Test_Messenger.Request.cs" />
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<Compile Include="$(MSBuildThisFileDirectory)Test_ObservableObject.cs" />

‎tests/CommunityToolkit.Mvvm.UnitTests/Test_Messenger.Observables.cs

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// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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// See the LICENSE file in the project root for more information.
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using System;
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using System.Collections.Generic;
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using CommunityToolkit.Mvvm.Messaging;
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using Microsoft.VisualStudio.TestTools.UnitTesting;
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namespace CommunityToolkit.Mvvm.UnitTests;
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partial class Test_Messenger
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{
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[TestMethod]
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[DataRow(typeof(StrongReferenceMessenger))]
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[DataRow(typeof(WeakReferenceMessenger))]
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public void Test_Messenger_CreateObservable(Type type)
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{
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IMessenger messenger = (IMessenger)Activator.CreateInstance(type)!;
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IObservable<MessageA> observable = messenger.CreateObservable<MessageA>();
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Assert.IsNotNull(observable);
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List<MessageA> messages = new();
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IDisposable disposable = observable.Subscribe(messages.Add);
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MessageA message1 = new();
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MessageA message2 = new();
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_ = messenger.Send(message1);
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_ = messenger.Send(message2);
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// The expected messages have been observed
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CollectionAssert.AreEqual(messages, new[] { message1, message2 });
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disposable.Dispose();
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_ = messenger.Send<MessageA>();
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// No messages are sent after unsubscribing the observable
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CollectionAssert.AreEqual(messages, new[] { message1, message2 });
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}
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[TestMethod]
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[DataRow(typeof(StrongReferenceMessenger))]
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[DataRow(typeof(WeakReferenceMessenger))]
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public void Test_Messenger_CreateObservable_WithToken(Type type)
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{
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IMessenger messenger = (IMessenger)Activator.CreateInstance(type)!;
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IObservable<MessageA> observable = messenger.CreateObservable<MessageA, int>(42);
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Assert.IsNotNull(observable);
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List<MessageA> messages = new();
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IDisposable disposable = observable.Subscribe(messages.Add);
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MessageA message1 = new();
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MessageA message2 = new();
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_ = messenger.Send(message1, 42);
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_ = messenger.Send(message2, 42);
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_ = messenger.Send(new MessageA(), 1);
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_ = messenger.Send(new MessageA(), 999);
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// The expected messages have been observed (only for matching tokens)
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CollectionAssert.AreEqual(messages, new[] { message1, message2 });
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disposable.Dispose();
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_ = messenger.Send(new MessageA(), 42);
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_ = messenger.Send(new MessageA(), 1);
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// No messages are sent after unsubscribing the observable (regardless of token)
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CollectionAssert.AreEqual(messages, new[] { message1, message2 });
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}
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[TestMethod]
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[ExpectedException(typeof(ArgumentNullException))]
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public void Test_Messenger_CreateObservable_NullMessenger()
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{
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_ = IMessengerExtensions.CreateObservable<MessageA>(null!);
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}
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[TestMethod]
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[ExpectedException(typeof(ArgumentNullException))]
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public void Test_Messenger_CreateObservable_WithToken_NullMessenger()
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{
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_ = IMessengerExtensions.CreateObservable<MessageA, string>(null!, "Hello");
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}
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[TestMethod]
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[ExpectedException(typeof(ArgumentNullException))]
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public void Test_Messenger_CreateObservable_WithToken_NullToken()
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{
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_ = IMessengerExtensions.CreateObservable<MessageA, string>(new WeakReferenceMessenger(), null!);
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}
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}

‎tests/CommunityToolkit.Mvvm.UnitTests/Test_Messenger.Request.cs

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namespace CommunityToolkit.Mvvm.UnitTests;
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public partial class Test_Messenger
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partial class Test_Messenger
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{
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[TestMethod]
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[DataRow(typeof(StrongReferenceMessenger))]

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