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    <p>Ideally what you want to do, is do as much heavy lifting as possible on a different thread to the UI thread. You then use some strategy to join back onto the UI thread to apply the result of the heavy lifting.</p> <p>The simplest approach I've found is to use a Task with a continuation, using 2 different TaskSchedulers. I think there is an easier way using async/await, but I'm not familiar enough with it to comment with any authority.</p> <p>Using your example:</p> <pre><code>private int? _Woo; public int? Woo { get { if (!_Woo.HasValue) { var task = Task.Factory.StartNew&lt;int&gt;(model.GetWoo, CancellationToken.None, TaskCreationOptions.None, TaskScheduler.Default()); task.ContinueWith(a =&gt; { _Woo = a.Result; }, CancellationToken.None, TaskContinuationOptions.OnlyOnRanToCompletion, TaskScheduler.FromCurrentSynchronizationContext()); } return _Woo; } set { _Woo = value; NotifyPropertyChange("Woo"); } } </code></pre> <p>Note that the heavy lifting task is scheduled using the Default TaskScheduler (meaning it will execute on a thread obtained from the ThreadPool) while the continuation is scheduled using the current synchronization context TaskScheduler (meaning it will execute back on whatever thread originally called Get).</p> <p>Usually I would inject the 2 TaskSchedulers (Background and Foreground/UI) into the ViewModel so that I could control the scheduling strategy for unit tests, but I've just hard referenced Default and FromCurrentSynchronizationContext in the example above.</p> <p><em>(Side Note: I'm not entirely sure what your sample code was trying to accomplish, if anything. I switched it up so that it is now essentially an asynchronous Get. The UI will ask for the value of Woo, which will trigger an asynchronous refresh using a Task and return instantly with its current NULL value. As soon as GetWoo finishes, it will set the value of Woo on the View Model, which will trigger a Property Changed event (on the correct thread), which will cause the UI to update the value of Woo on the screen. I think it shows the concept of doing the heaving lifting off the UI thread anyway.)</em></p>
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