How can I integrate IHttpClientFactory and Polly with a custom IoC container in MvvmCross

1. Choose a Custom IoC Container**

MvvmCross uses its own IoC container by default, but you can replace it with a custom one like Microsoft's Dependency Injection (DI) container. This is beneficial for integrating third-party libraries such as `IHttpClientFactory` and Polly more easily.

2. Implement a Custom IoC Adapter**

To use a custom IoC container with MvvmCross, you need to create an adapter that implements `IMvxIoCProvider`. This adapter will map your custom IoC implementation to the MvvmCross interface.

Here’s an example using Microsoft's DI container:

csharp
public class HostingAdapter : MvxSingleton, IMvxIoCProvider
{
    private IServiceProvider ServiceProvider;
    private IServiceCollection ServiceCollection;

    public HostingAdapter()
    {
        var host = Host.CreateDefaultBuilder()
            .ConfigureServices((context, serviceCollection) =>
            {
                ConfigureServices(context, serviceCollection);
                ServiceCollection = serviceCollection;
            })
            .Build();

        ServiceProvider = ServiceCollection.BuildServiceProvider();
    }

    public void ConfigureServices(IServiceCollection services)
    {
        // Register services here
    }

    public void RegisterType() where TFrom : class where TTo : class, TFrom
    {
        ServiceCollection.AddTransient();
        ServiceProvider = ServiceCollection.BuildServiceProvider();
    }

    public T GetSingleton() where T : class
    {
        return ServiceProvider.GetRequiredService();
    }

    public object GetSingleton(Type type)
    {
        return ServiceProvider.GetRequiredService(type);
    }
}

3. Override MvvmCross IoC Creation**

In your platform-specific setup class, override the creation of the IoC provider to return your custom adapter:

csharp
protected override IMvxIoCProvider CreateIocProvider()
{
    var hostingAdapter = new HostingAdapter();
    return hostingAdapter;
}

4. Register IHttpClientFactory and Polly**

In the `ConfigureServices` method of your adapter, register `IHttpClientFactory` and Polly policies:

csharp
public void ConfigureServices(IServiceCollection services)
{
    services.AddHttpClient("PollyWaitAndRetry")
        .AddTransientHttpErrorPolicy(policyBuilder =>
            policyBuilder.WaitAndRetryAsync(
                3, retryNumber => TimeSpan.FromMilliseconds(600)));

    // Or for exponential backoff
    var retryPolicy = Policy.HandleTransientHttpError()
        .OrResult(r => r.StatusCode == HttpStatusCode.NotFound)
        .WaitAndRetryAsync(6, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)));

    services.AddHttpClient("ExponentialBackoff")
        .AddPolicyHandler(retryPolicy);
}

5. Use IHttpClientFactory in Your Services**

Inject `IHttpClientFactory` into your services and use it to create clients:

csharp
public class MyService
{
    private readonly IHttpClientFactory _httpClientFactory;

    public MyService(IHttpClientFactory httpClientFactory)
    {
        _httpClientFactory = httpClientFactory;
    }

    public async Task DoSomethingAsync()
    {
        var client = _httpClientFactory.CreateClient("PollyWaitAndRetry");
        // Use the client to make HTTP requests
    }
}

6. Register MvvmCross Services**

Ensure that all necessary MvvmCross services are registered in your custom IoC container. This might involve manually registering services like `IMvxLoggerProvider`, `IMvxSettings`, etc., if they are not automatically registered by MvvmCross.

Conclusion

Integrating `IHttpClientFactory` and Polly with a custom IoC container in MvvmCross requires creating an adapter for your chosen IoC container, overriding MvvmCross's IoC creation, and registering the necessary services. This approach allows you to leverage the benefits of `IHttpClientFactory` and Polly's resilience policies within the MvvmCross framework.