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    <p>With the later .Net Frameworks (4.0+) and WPF you can utilize the <a href="http://msdn.microsoft.com/en-us/library/system.threading.tasks.aspx" rel="nofollow"><code>System.Threading.Tasks</code></a> library to provide a lot of this work under the hood.</p> <p>If say your Command on your needs to update a property on your View Model, but it has to wait for the information, you simply start a task to perform the IO:</p> <pre><code>this.FindDataCommand = new RelayCommand&lt;string&gt;( /* ICommand.Execute */ value =&gt; { Task.Factory .StartNew&lt;IEnumerable&lt;Foo&gt;&gt;(() =&gt; FindData(value)) .ContinueWith( task =&gt; { this.foundData.Clear(); this.foundData.AddRange(task.Result); }, TaskScheduler.FromCurrentSynchronizationContext()); }, /* ICommand.CanExecute */ value =&gt; !String.IsNullOrWhitespace(value)); </code></pre> <p>Breaking this down into manageable parts, we're <a href="http://msdn.microsoft.com/en-us/library/dd321421.aspx" rel="nofollow">starting a new task</a> which calls some method <code>IEnumerable&lt;Foo&gt; FindData(string)</code>. This is the plain old boring synchronous code you've always written. Likely it already exists on your view model!</p> <p>Next we tell the framework to <a href="http://msdn.microsoft.com/en-us/library/dd270696.aspx" rel="nofollow">start a new task when that one finishes</a> using <code>ContinueWith</code>, but to do it on the <a href="http://blog.lab49.com/archives/4034" rel="nofollow">WPF Dispatcher instead</a>. This allows you to avoid the hassles of cross-thread problems with UI elements.</p> <p>You can extend this for monitoring with a helper class:</p> <pre><code>public class TaskManager { private static ConcurrentDictionary&lt;Dispatcher, TaskManager&gt; _map = new ConcurrentDictionary&lt;Dispatcher, TaskManager&gt;(); public ObservableCollection&lt;WorkItem&gt; Running { get; private set; } public TaskManager() { this.Running = new ObservableCollection&lt;WorkItem&gt;(); } public static TaskManager Get(Dispatcher dispatcher) { return _map.GetOrAdd(dispatcher, new TaskManager()); } // ... </code></pre> <p>Using this class in XAML would be along the lines of adding its instance to your Window's <code>ViewModel</code>:</p> <pre><code>public TaskManager CurrentTaskManager { get { return TaskManager.Get(Dispatcher.CurrentDispatcher); } } // &lt;StatusBarItem Content="{Binding CurrentTaskManager.Running.Count}" /&gt; </code></pre> <p>You would then add a method to your TaskManager to handle the adding of tasks to and from the Running collection:</p> <pre><code> public Task&lt;TResult&gt; StartNew&lt;TResult&gt;(Func&lt;TResult&gt; work) { var task = Task.Factory .StartNew&lt;TResult&gt;(work); // build our view model var workItem = new WorkItem(task); this.Running.Add(workItem); // Pass the result back using ContinueWith return task.ContinueWith( t =&gt; { this.Running.Remove(workItem); return t.Result; }, TaskScheduler.FromCurrentSynchronizationContext()); } </code></pre> <p>Now we simply change our <code>FindDataCommand</code> implementation:</p> <pre><code>TaskManager.Get(Dispatcher.CurrentDispatcher) .StartNew&lt;IEnumerable&lt;Foo&gt;&gt;(() =&gt; FindData(value)) .ContinueWith( task =&gt; { this.foundData.Clear(); this.foundData.AddRange(task.Result); }, TaskScheduler.FromCurrentSynchronizationContext()); </code></pre> <p>The <code>WorkItem</code> class could expose the properties on the <code>Task</code> class to the UI, or it could be extended to encapsulate a <code>CancellationToken</code> to support cancellation in the future.</p>
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    1. COThanks for the snippet and detailed explanation. Seems like I have reinvented the wheel (again). But my main problem is that I also want to display pending operations/tasks/WorkItems in the StatusBar of the Window. For that to work I need to find the one and only WorkQueue of the Window in which the Command has been triggered.
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    2. CO@Korexio: you can add a helper class to encapsulate starting new tasks and use that to track them. Then borrowing from the Task framework you can use it to remove finished items. A bit more work is required to support handling the different statuses of tasks, but that would be another question. I hope this helps.
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    3. COThanks for the really GREAT example. That's exactly what I was looking for. Thanks for your help!
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