System.Threading.Tasks and updating the UI thread

This is something that I couldn't remember parts of earlier today so I figured I would add it to my "knowledge base". I wanted to retrieve a TFS work item on a background thread in my ViewModel and have the UI update when complete. Specifically I wanted to retrieve the title of a TFS work item (project here) and have that display after the user entered a work item id. While this is not a terribly expensive server hit, it can be noticeable enough to want it performed on another thread.

In the end the method associated with my RelayCommand looked like the below:

private void CheckWorkItemId()
{
    if (!this.WorkItemIdInvalidated || this.ProjectId <= 0
    || string.IsNullOrWhiteSpace(Settings.Default.TfsServerName))
        return;
   
    this.WorkItemTitle = WORK_ITEM_FETCH;
   
    Task.Factory.StartNew(() => WorkItemInfoRetriever.Get(
        Settings.Default.TfsServerName, this.ProjectId)).ContinueWith(t =>
        {
            if (null == t.Exception)
            {
                this.WorkItemTitle = t.Result.Title;
                this.WorkItemIdInvalidated = false;
            }
            else
            {
                this.WorkItemTitle = null;
                var ex = t.Exception.InnerException;
                if (ex is InvalidWorkItemException)
                    _messageBoxService.ShowOKDispatch(ex.Message, "Invalid Work Item");
                else
                    _messageBoxService.ShowErrorDispatch(ex.Message, "Unexpected Error");
            }

            ReCalculateCommands();
        }, TaskScheduler.FromCurrentSynchronizationContext());
}

The salient points are:

    Grabbing the current task scheduler while on the UI thread with TaskScheduler.FromCurrentSynchronizationContext, done in the ContinueWith call
    Chaining in a continuation to be run when the task completes via Task.ContinueWith
    Checking for exception when completed. I bypassed explicit use of AggregateException and InnerExceptions as in my case there'd be a single error or none

Read more: geoffhudik.com
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