MessengerPageViewModel.cs

// 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 Microsoft.Toolkit.Mvvm.ComponentModel;
using Microsoft.Toolkit.Mvvm.Messaging;
using Microsoft.Toolkit.Mvvm.Messaging.Messages;

namespace MvvmSample.ViewModels
{
    public class MessengerPageViewModel : SamplePageViewModel
    {
        public UserSenderViewModel SenderViewModel { get; } = new UserSenderViewModel();

        public UserReceiverViewModel ReceiverViewModel { get; } = new UserReceiverViewModel();

        // Simple viewmodel for a module sending a username message
        public class UserSenderViewModel : ObservableRecipient
        {
            private string username = "Bob";

            public string Username
            {
                get => username;
                private set => SetProperty(ref username, value);
            }

            protected override void OnActivated()
            {
                Messenger.Register<CurrentUsernameRequestMessage>(this, (r, m) => m.Reply(Username));
            }

            public void SendUserMessage()
            {
                Username = Username == "Bob" ? "Alice" : "Bob";

                Messenger.Send(new UsernameChangedMessage(Username));
            }
        }

        // Simple viewmodel for a module receiving a username message
        public class UserReceiverViewModel : ObservableRecipient
        {
            private string username = "";

            public string Username
            {
                get => username;
                private set => SetProperty(ref username, value);
            }

            protected override void OnActivated()
            {
                Messenger.Register<UsernameChangedMessage>(this, (r, m) => Username = m.Value);
            }
        }

        private string username;

        public string Username
        {
            get => username;
            private set => SetProperty(ref username, value);
        }

        public void RequestCurrentUsername()
        {
            Username = WeakReferenceMessenger.Default.Send<CurrentUsernameRequestMessage>();
        }

        public void ResetCurrentUsername()
        {
            Username = null;
        }

        // A sample message with a username value
        public sealed class UsernameChangedMessage : ValueChangedMessage<string>
        {
            public UsernameChangedMessage(string value) : base(value)
            {
            }
        }

        // A sample request message to get the current username
        public sealed class CurrentUsernameRequestMessage : RequestMessage<string>
        {
        }
    }
}