Propagating Changes Across the App

Problem

In modern applications, it's essential to manage and propagate state changes across different parts of the application efficiently.

Solution

The IMessenger interface provided by Uno.Extensions allows components to communicate effectively without tight coupling, using messages to signify state changes. This pattern is particularly useful in managing reactive updates across different layers of the application, such as services and view models.

Setup

Ensure IMessenger is registered in your application's services during startup in the ConfigureServices method:

host.ConfigureServices((context, services) =>
{
    services
        ... // other services
        .AddSingleton<IMessenger, WeakReferenceMessenger>();
})

Using IMessenger in Services

Inject the IMessenger into the CookbookService:

public class CookbookService(ChefsApiClient client, IMessenger messenger, IUserService userService): ICookbookService
{
    ...
}

When a cookbook is created, updated, or deleted, send a message to notify subscribers:

public async ValueTask Update(Cookbook cookbook, CancellationToken ct)
{
    var cookbookData = cookbook.ToData();

    await client.Api.Cookbook.PutAsync(cookbookData, cancellationToken: ct);
    messenger.Send(new EntityMessage<Cookbook>(EntityChange.Updated, cookbook));
}

Reacting to Changes in ViewModels

Subscribe to messages in the ViewModel to react to changes in the service:

public IState<Cookbook> Cookbook => State
    .Value(this, () => _cookbook ?? new Cookbook())
    .Observe(_messenger, cb => cb.Id);