How to use WeakReferenceMessenger in MAUI?

I didn't get a clear picture of how to use WeakReferenceMessenger in MAUI after reading this blog.

I am using MessagingCenter in my xamarin forms app like below.

//Send message
MessagingCenter.Send<ModePage>(this, "modechanged");

//Subscribe message and actions
MessagingCenter.Subscribe<ModePage>(this, "modechanged", (sender) =>
{
    SetMode();
});

Please show me the equivalent usage of the above code using WeakReferenceMessenger? In WeakReferenceMessenger where I need to pass the key and to subscribe with key?

MessagingCenter has been deprecated in .NET 7 and replaced with WeakReferenceMessenger in the CommunityToolkit.Mvvm NuGet package.

Below are the detailed steps on how to use WeakReferenceMessenger in MAUI:

1. Install the CommunityToolkit.Mvvm NuGet package into your project.

2. Define a message class: SendItemMessage.cs that you want to send across different parts or pages of your MAUI app like below:

public class SendItemMessage : ValueChangedMessage<string> 
{
    public SendItemMessage(string value) : base(value)
    {
    }
}

3. Sending the messages: You need to pass an instance of the message class to the Send method like below:

WeakReferenceMessenger.Default.Send(new SendItemMessage("Model Changed"));

4. Receiving the messages: You need to register a message handler for the message class like below:

WeakReferenceMessenger.Default.Register<SendItemMessage>(this, (r, m) =>
{
     OnMessageReceived(m.Value);
});

Here's the sample code below for your reference:

MainPage.cs:

public partial class MainPage : ContentPage 
{
      public MainPage(MainPageViewModel viewModel)
      {
            InitializeComponent();
            BindingContext = viewModel;
      }

      private void OnCounterClicked(object sender, EventArgs e)
      {
            WeakReferenceMessenger.Default.Send(new SendItemMessage("Model Changed"));
      }
}

MainPage.xaml:

<Button 
    x:Name="CounterBtn"
    Text="Click me"
    Clicked="OnCounterClicked"
    HorizontalOptions="Center" />

MainPageViewModel.cs:

public class MainPageViewModel
{
        public  MainPageViewModel()      
        {
            WeakReferenceMessenger.Default.Register<SendItemMessage>(this, (r, m) =>
            {
                OnMessageReceived(m.Value);
            });            
        }

        private static void OnMessageReceived(string value)
        {
            Shell.Current.DisplayAlert("Messages received", value, "OK");
        }
}

Another cool way to register message handlers by using the IRecipient<TMessage> interface to register message handlers.

public class MainPageViewModel: IRecipient<SendItemMessage> 
{
        public  MainPageViewModel()            
        {

            WeakReferenceMessenger.Default.Register(this);  
        }

        public void Receive(SendItemMessage message)
        {
            Shell.Current.DisplayAlert("Messages received", message.Value, "OK");
         }
    }

Update:

public class SendItemMessage : ValueChangedMessage<string> 
{
    public SendItemMessage(string value) : base(value)
    {
    }
}

The ValueChangedMessage<T> class is a generic class that represents a message that contains a value of type T that has been changed. Since the SendItemMessage implements the ValueChangedMessage<string>, the generic parameter <string> specifies the type of the value that the message carries. In the example above, the value is a string. You can define the type of the value according to your own design, like a simple datatype:int,bool, or even a class model, etc.