WP7Contrib: Network Connectivity Push Model

To start my WP7Contrib blogging contribution I thought I started with something small, easy and relatively quick to explain. If you're familiar with the platform you can get the current network type using the API - NetworkInterface.NetworkInterfaceType. This is a simple synchronous call which returns what MSDN describes as 'the type of the network servicing Internet requests. This is a prime example of a 'pull model' to obtain data.

We've turned this model on its head, and produced a 'push model' using the MS Reactive Extensions for .Net.

What we did was use an observable sequence which returns values at a specified frequency using the interval method.

this.networkObserver = Observable.Interval(TimeSpan.FromMilliseconds(frequency))
   .Select(DetermineCurrentStatus)
   .Subscribe(this.statusSubject);

So for every interval we execute the Select and the returned value from DetermineCurrentStatus is pushed to the statusSubject. This is a behavior subject and this is specifically designed to store a value that changes over time.

We then expose this via an instance of the interface IObservable and use the DistinctUntilChanged to return the last distinct value.

public IObservable Status()
{
return this.statusSubject.DistinctUntilChanged();
}

The implementation can be found in the NetworkMonitor class, in the WP7Contrib.Communications assembly.

I have shown an extract of a quick example application called 'Network Monitor Demo' below (the code can be found here.). I've done this in the "code behind" for simplicity so there are no distractions of view models or DI etc.

In this example I display the last type and the type history overtime, see screenshot below - click 'Start' to see the NetworkMonitor in action.

public partial class MainPage : PhoneApplicationPage
{
private readonly INetworkService networkService;
private readonly IObservableCollection<TypeHistory> history = new ObservableCollection<TypeHistory>();
private IDisposable statusObserver;
// Constructor
public MainPage()
{
InitializeComponent();
this.networkService = new NetworkMonitor(10000);
this.typeHistory.ItemsSource = this.history;
}
private void start_Click(object sender, RoutedEventArgs e)
{
if (this.statusObserver != null)
 return;

this.statusObserver = this.networkService.Status()
 .ObserveOnDispatcher()
 .Subscribe(type =>
                {
                    this.lastType.Text = type.ToString();
                    this.history.Add(new TypeHistory(type.ToString(), DateTime.Now));
                });
}
private void stop_Click(object sender, RoutedEventArgs e)
{
if (this.statusObserver == null)
 return;

this.statusObserver.Dispose();
this.statusObserver = null;
}
}

public class TypeHistory
{
public string Type { get; private set; }
public DateTime Time { get; private set; }
public TypeHistory(string type, DateTime time)
{
this.Type = type;
this.Time = time;
}

public override string  ToString()
{
return string.Format("{0} - {1}", this.Time.ToUniversalTime(), this.Type);
}
}

And that pretty much covers our push model for network connectivity, thanks for getting this far :)

If you're wondering how I did the screenshot from the phone check out Laurent Bugnion post on the subject.