How do synchronous Polly policies integrate with MvvmCross data binding

Understanding Polly and MvvmCross

Polly

MvvmCross

Integrating Polly with MvvmCross Data Binding

To integrate Polly's synchronous policies with MvvmCross data binding, you need to ensure that your application's data retrieval or manipulation logic is wrapped in Polly policies. Here’s how you can achieve this:

1. Implementing Polly Policies:
- Create a Polly policy that handles synchronous operations. For example, you might use a retry policy to handle transient faults when fetching data from a database or API.
- Use the `Policy` class for synchronous operations, which does not return a `Task` but instead executes the action directly[1].

2. Integrating with MvvmCross Data Binding:
- In your ViewModel, use the Polly policy to wrap any data retrieval or manipulation logic. This ensures that if there are transient faults, the policy will automatically retry the operation.
- Use MvvmCross's data binding features to bind the retrieved or manipulated data to your View. This will automatically update the UI when the data changes.

3. Example Implementation:
- Suppose you have a method `GetData()` that fetches data from an API. You can wrap this method in a Polly retry policy to handle any transient faults.
- In your ViewModel, use this wrapped method to fetch data and then bind it to your View using MvvmCross's data binding.

csharp
// Define a Polly retry policy
var retryPolicy = Policy.Handle()
    .WaitAndRetry(3, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)));

// Use the policy in your ViewModel to fetch data
public class MyViewModel : MvxViewModel
{
    private string _data;

    public string Data
    {
        get => _data;
        set => SetProperty(ref _data, value);
    }

    public async Task FetchDataAsync()
    {
        // Note: Even though FetchDataAsync is async, the inner Polly policy is sync.
        // You might need to adapt this based on your actual async requirements.
        retryPolicy.Execute(() =>
        {
            // Simulate synchronous data retrieval (e.g., from a local cache or a sync API call)
            Data = GetDataSync();
        });
    }

    private string GetDataSync()
    {
        // Simulate synchronous data retrieval logic here
        return "Sample Data";
    }
}

4. Data Binding in MvvmCross:
- Once you have fetched the data using Polly's retry policy, you can bind it to your View using MvvmCross's data binding features.
- Ensure that your View is properly configured to display the bound data.

csharp
// In your View (e.g., a Xamarin.Forms page)
public class MyView : MvxContentPage
{
    public MyView()
    {
        InitializeComponent();

        // Assuming you have a Label to display the data
        var dataLabel = new Label();
        dataLabel.SetBinding(Label.TextProperty, nameof(MyViewModel.Data));
        Content = dataLabel;
    }
}

By integrating Polly's synchronous policies with MvvmCross data binding, you can enhance your application's resilience and responsiveness, ensuring that transient faults do not disrupt the user experience.