As promised, here is a blog post which shares source code and slides for the Rx talk I gave during last TechDays in Paris. I animated this session with my co-worker Charlotte and with Mitsu.

Download slides here.
Download source code here.

Demo1: Drag’n’drop in a WPF application

The goal was to implement a basic drag’n’drop functionality in a WPF application. The Rx query looks like the following:

var query = from mouseDown in this.image.GetMouseLeftButtonDownObservable()
            let downPosition = mouseDown.EventArgs.GetPosition(this)
            let rect = new Rect(downPosition.X - 10, downPosition.Y - 10, 20, 20)
            let delta = mouseDown.EventArgs.GetPosition(this.image)
            from mouseMove in this.GetMouseMoveObservable()
                .Select(ea => ea.EventArgs.GetPosition(this))
                .SkipWhile(p => rect.Contains(p))
                .DoOnce(p => this.onMouseEnter.Begin(this.image))
                .Select(p => p.Offset(delta))
                .TakeUntil(this.GetMouseLeftButtonUpObservable())
                .Finally(() => this.onMouseLeave.Begin(this.image))
            select mouseMove;

query.Subscribe(p => this.image.SetPosition(p));

Demo2: online Twitter search and Bing map geolocalization

This time, the goal was to query Twitter asynchronously and to geolocalize the associated Tweets. The Rx query:

this.textbox.GetTextChangedObservable()
    .DistinctUntilChanged((ea) => this.textbox.Text)
    .Throttle(TimeSpan.FromMilliseconds(300))
    .ObserveOnDispatcher()
    .Do(ea => this.ShowLoadingIndicator())
    .Select(ea => TweeterHelper.Search(this.textbox.Text))
    .Switch()
    .ObserveOn(Scheduler.Dispatcher)
    .Select(page => TweeterHelper.ParseTwitterSearch(page))
    .Subscribe((tweets) =>
                    {
                        this.HideLoadingIndicator();
                        this.listbox.ItemsSource = tweets;

                        TweeterHelper.LocalizeTweets(this.map, tweets);
                    });

Demo3: using the accelerometer in a Windows Phone 7 application

The last demo was about the usage of the accelerometer in a Windows Phone 7 application. Here is the relevant Rx query:

private void MoveEllipse(IObservable accelerationObservable)
{
    accelerationObservable
        .SlidingBuffer(2)
        .Select(accCouple => new Acceleration(accCouple.First(), accCouple.Last()))
        .ObserveOnDispatcher()
        .Do(acc => this.textBlock.Text = acc.ToString())
        .Scan(new Point(x0, y0), (point, acc) => point.Move(acc).ClipTo(horizontalInterval, verticaInterval))
        .Subscribe(p => this.ellipse.SetCenter(p));
}

Doing this session was a really great experience ! I’d like to thank Charlotte and Mitsu for doing it with me. Also, I’d like to thank all users who came to the presentation !

During the next 3 days, the “Palais des Congrès” in Paris will hosting the TechDays 2011. For the very first time, I’ll have the chance to be part of it as a speaker for a talk about Rx (Reactive Extensions).

The session will take place in room 241, tomorrow Thursday 8, from 1pm to 2pm. Here is the link to the session’s description (in French).

I’ll share presentation slides and source code by the end of the week 🙂