Convert Polling Web Service to RX

Question

Given:

public partial class Weather
{
    private readonly DispatcherTimer _timer = new DispatcherTimer();
    private readonly IWeatherDataProvider _weatherDataProvider;

    public Weather(IWeatherDataProvider weatherDataProvider)
    {
        InitializeComponent();
        _weatherDataProvider = weatherDataProvider;
        Loaded += async (sender, args) =>
        {
            _timer.Interval = new TimeSpan(0, 15, 0);
            _timer.Tick += async (o, eventArgs) => DataContext = await UpdateWeather();
            _timer.Start();
            DataContext = await UpdateWeather();
        };

        Unloaded += (sender, args) => _timer.Stop();
    }

    private async Task<WeatherData> UpdateWeather()
    {
        var weatherData = await _weatherDataProvider.GetWeather();
        return weatherData;
    }
}

I'm puzzling how to convert this use Reactive Extensions. I started with:

var weather = Observable.FromAsync(_weatherDataProvider.GetWeather);

But when I got to the polling part:

Observable.Timer(new TimeSpan(0, 15, 0)).Subscribe(weather);

There is no generic overload. I think I get the idea that I need to generate a sequence but I just can't puzzle it out for some reason.

Answer 1

Observable.Interval with a Select projection is the key. Something like this:

public class Weather
{
    private readonly IWeatherDataProvider _weatherDataProvider;        
    private CompositeDisposable disposables = new CompositeDisposable();

    public Weather(IWeatherDataProvider weatherDataProvider)
    {
        InitializeComponent();
        _weatherDataProvider = weatherDataProvider;

        Loaded += (sender, args) =>
        {
          var weather = Observable.Interval(TimeSpan.FromMinutes(15))
              .SelectMany(_ => weatherDataProvider.GetWeather().ToObservable())
              .ObserveOnDispatcher()
              .Subscribe(data => DataContext = data);
          disposables.Add(weather);
        };

        Unloaded += (sender, args) => disposables.Dispose();
    }
}

ObserveOnDispatcher is in nuget package rx-xaml.