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copied!<blockquote> <p>Will this fire?</p> </blockquote> <p>Nope, this will only fire when you <em>set</em> the list:</p> <pre><code>TweetTiles = new List<TweetTileViewModel>(); </code></pre> <blockquote> <p>I have a function, running on a background Task, that is returning tweets. Each time I get a new tweet I convert it to a TweetTileViewModel and want it to show in my UI listbox.</p> </blockquote> <p>ReactiveUI has built-in support for this, via the <code>ReactiveList</code> class. Here's how you want to set it up - first, declare some properties:</p> <pre><code>ReactiveList<Tweet> Tweets { get; protected set; } IReactiveDerivedList<TweetTileViewModel> TweetViewModels { get; protected set; } ReactiveCommand LoadTweets { get; protected set; } </code></pre> <p>Then, in the constructor:</p> <pre><code>// Note: Only change this list on the UI thread! Tweets = new ReactiveList<Tweet>(); // Now, TweetViewModels will "follow around" Tweets as you add and remove items TweetViewModels = Tweets.CreateDerivedCollection( tweet => new TweetTileViewModel(tweet)); LoadTweets = new ReactiveCommand(); var newTweets = LoadTweets.RegisterAsyncTask(async _ => { // Loads the latest tweets return LoadTweetsAsync(); }); newTweets.Subscribe(newTweets => { // Add in the new tweets we downloaded. This is guaranteed by // ReactiveCommand to be on the UI thread Tweets.AddRange(newTweets); }); </code></pre> <p><strong>Update:</strong> Fixed type error. To use a method that only sends a callback, use an AsyncSubject:</p> <pre><code>public IObservable<List<Tweet>> GetTweetsObservable(this TwitterClient This) { var ret = new AsyncSubject<List<Tweet>>(); try { This.GetTweetsWithCallback(tweets => { ret.OnNext(tweets); ret.OnCompleted(); }); } catch (Exception ex) { ret.OnError(ex); } return ret; } </code></pre> <p>Now, you can change <code>RegisterAsyncTask</code> to just <code>RegisterAsync</code> and you're good to go!</p>

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