Skip to main content

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.

Comments

Post a Comment

Popular posts from this blog

WPF tips & tricks: Dispatcher thread performance

Not blogged for an age, and I received an email last week which provoked me back to life. It was a job spec for a WPF contract where they want help sorting out the performance of their app especially around grids and tabular data. I thought I'd shared some tips & tricks I've picked up along the way, these aren't probably going to solve any issues you might be having directly, but they might point you in the right direction when trying to find and resolve performance issues with a WPF app. First off, performance is something you shouldn't try and improve without evidence, and this means having evidence proving you've improved the performance - before & after metrics for example. Without this you're basically pissing into the wind, which can be fun from a developer point of view but bad for a project :) So, what do I mean by ' Dispatcher thread performance '? The 'dispatcher thread' or the 'UI thread' is probably the most

Showing a message box from a ViewModel in MVVM

I was doing a code review with a client last week for a WPF app using MVVM and they asked ' How can I show a message from the ViewModel? '. What follows is how I would (and have) solved the problem in the past. When I hear the words ' show a message... ' I instantly think you mean show a transient modal message box that requires the user input before continuing ' with something else ' - once the user has interacted with the message box it will disappear. The following solution only applies to this scenario. The first solution is the easiest but is very wrong from a separation perspective. It violates the ideas behind the Model-View-Controller pattern because it places View concerns inside the ViewModel - the ViewModel now knows about the type of the View and specifically it knows how to show a message box window: The second approach addresses this concern by introducing the idea of messaging\events between the ViewModel and the View. In the example below

Implementing a busy indicator using a visual overlay in MVVM

This is a technique we use at work to lock the UI whilst some long running process is happening - preventing the user clicking on stuff whilst it's retrieving or rendering data. Now we could have done this by launching a child dialog window but that feels rather out of date and clumsy, we wanted a more modern pattern similar to the way <div> overlays are done on the web. Imagine we have the following simple WPF app and when 'Click' is pressed a busy waiting overlay is shown for the duration entered into the text box. What I'm interested in here is not the actual UI element of the busy indicator but how I go about getting this to show & hide from when using MVVM. The actual UI elements are the standard Busy Indicator coming from the WPF Toolkit : The XAML behind this window is very simple, the important part is the ViewHost. As you can see the ViewHost uses a ContentPresenter element which is bound to the view model, IMainViewModel, it contains 3 child v