How should I update from Task the UI Thread?

Here is a good article: Parallel Programming: Task Schedulers and Synchronization Context.

Take a look at Task.ContinueWith() method.

Example:

var context = TaskScheduler.FromCurrentSynchronizationContext();var task = new Task<TResult>(() =>    {        TResult r = ...;        return r;    });task.ContinueWith(t =>    {        // Update UI (and UI-related data) here: success status.        // t.Result contains the result.    },    CancellationToken.None, TaskContinuationOptions.OnlyOnRanToCompletion, context);task.ContinueWith(t =>    {        AggregateException aggregateException = t.Exception;        aggregateException.Handle(exception => true);        // Update UI (and UI-related data) here: failed status.        // t.Exception contains the occured exception.    },    CancellationToken.None, TaskContinuationOptions.OnlyOnFaulted, context);task.Start();

Since .NET 4.5 supports async/await keywords (see also Task.Run vs Task.Factory.StartNew):

try{    var result = await Task.Run(() => GetResult());    // Update UI: success.    // Use the result.}catch (Exception ex){    // Update UI: fail.    // Use the exception.}

You need to run the ContinueWith -task on the UI thread. This can be accomplished using the TaskScheduler of the UI thread with the overloaded version of the ContinueWith -method, ie.

TaskScheduler scheduler = TaskScheduler.Current;...ContinueWith(obj => LogContent = obj.Result), CancellationToken.None, TaskContinuationOptions.None, scheduler)

You can use the Dispatcher to invoke code on UI thread. Take a look at the article Working With The WPF Dispatcher