Can Polly be used to handle both synchronous and asynchronous operations in MvvmCross

Using Polly with MvvmCross

MvvmCross is a framework that supports cross-platform development and encourages the use of asynchronous programming to avoid blocking the UI thread. When integrating Polly into an MvvmCross application, you can leverage Polly's asynchronous policies to handle retries, timeouts, and other resilience strategies for asynchronous operations.

Asynchronous Operations

For asynchronous operations in MvvmCross, you can define an `AsyncPolicy` that handles retries or other resilience strategies. Here's an example of how you might use Polly to retry an asynchronous operation in an MvvmCross ViewModel:

csharp
using Polly;
using MvvmCross.ViewModels;

public class MyViewModel : MvxViewModel
{
    private readonly ISomeService _someService;
    private readonly AsyncPolicy> _retryPolicy;

    public MyViewModel(ISomeService someService)
    {
        _someService = someService;
        _retryPolicy = Policy.Handle()
            .RetryAsync(3, onRetryAsync: async (exception, retryCount, context) =>
            {
                // Handle retry logic here if needed
            });
    }

    public async Task Initialize()
    {
        await base.Initialize();
        await ExecuteWithRetryAsync();
    }

    private async Task ExecuteWithRetryAsync()
    {
        try
        {
            var result = await _retryPolicy.ExecuteAsync(async () =>
            {
                return await _someService.DoSomethingAsync();
            });
            // Process the result
        }
        catch (Exception ex)
        {
            // Handle any exceptions that occur after retries
        }
    }
}

Synchronous Operations

While Polly can handle synchronous operations, MvvmCross is designed to work with asynchronous code to keep the UI responsive. However, if you need to handle synchronous operations, you would use a synchronous policy (`Policy` or `Policy`). Polly does not support executing asynchronous code through synchronous policies directly, so you would need to ensure that any synchronous code executed through Polly does not block or attempt to await asynchronous operations.

MvxNotifyTask for Async Operations

MvvmCross provides `MvxNotifyTask`, which is useful for managing asynchronous operations and their state changes. While Polly handles resilience strategies, `MvxNotifyTask` can be used to monitor the state of tasks and notify the UI about changes, such as completion or exceptions.

csharp
public class MyViewModel : MvxViewModel
{
    private readonly ISomeService _someService;
    private MvxNotifyTask _myTaskNotifier;

    public MyViewModel(ISomeService someService)
    {
        _someService = someService;
    }

    public MvxNotifyTask MyTaskNotifier
    {
        get => _myTaskNotifier;
        private set => SetProperty(ref _myTaskNotifier, value);
    }

    public async Task Initialize()
    {
        await base.Initialize();
        MyTaskNotifier = MvxNotifyTask.Create(() => MyMethodAsync());
    }

    private async Task MyMethodAsync()
    {
        // Use Polly here if needed for resilience
        await _someService.DoSomethingAsync();
    }
}

In summary, Polly can be used with MvvmCross to handle both synchronous and asynchronous operations, but the focus should be on asynchronous policies for resilience strategies. MvvmCross's `MvxNotifyTask` is complementary, helping manage the state of asynchronous operations within the ViewModel.