title: WPF with UI threading issues - TaskFactory, CollectionView issues - syntax nightmare
body: <p>See bottom of post for my pseudo solution.</p>
  
  <p>Once again I'm completely and utterly stuck on this. I've burned hours trying to understand - and yes I can get a single collectionviewsource to work beautifully with nothing about threading on the code behind.</p>
  
  <p>Imagine my shock when I found merely adding two collectionviewsources on the page causes threading issues. I've spent a few hours last night reading Async in C#5 and the MSDN stuff however I get into work today and I can't decipher how to make this happen.</p>
  
  <p>The code below is the last attempt I've made before whining for help as I've burnt, possibly, a bit too much work time on attempting to understand how to do this. I understand that I need one collectionviewsource to complete before starting the other, so I tried Await Task.ContinueWith etc to try and chain one after the other.</p>
  
  <p>Lining up both sets of tasks in the threads correctly seems to be quite tricky, or I'm still misunderstanding something fundemental.</p>
  
  <p>If anyone can advise how they would asynchronously populate a few controls on a WPF UI I would be very grateful.</p>
  
  <p>The application itself is a throwaway application, linked to an Access database that I'm using to try and become fluent enough in threading to implement it in our proper code base. I'm long way off that!</p>
  
  <p>Updated with more complete code samples and the adjustments made according to answers:</p>
  
  <pre><code>Private Async Sub MainWindowLoaded(sender As Object, e As RoutedEventArgs) Handles MyBase.Loaded
  InitializeComponent()
  
  Dim personSetViewSource As System.Windows.Data.CollectionViewSource = CType(Me.FindResource("personSetViewSource"), System.Windows.Data.CollectionViewSource)
  Dim contactSetViewSource As System.Windows.Data.CollectionViewSource = CType(Me.FindResource("contactSetViewSource"), System.Windows.Data.CollectionViewSource)
  
  Dim personList = Await Task.Run(Function() personSet.personList)
  personSetViewSource.Source = personList
  
  Dim contactList = Await Task.Run(Function() contactSet.contactList)
  contactSetViewSource.Source = contactList
  
  End Sub`
  </code></pre>
  
  <p>The ObservableCollectionEx class:</p>
  
  <pre><code>public class ObservableCollectionEx&lt;T&gt; : ObservableCollection&lt;T&gt;
  {
  public override event NotifyCollectionChangedEventHandler CollectionChanged;
  
  protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
  {
      using (BlockReentrancy())
      {
          NotifyCollectionChangedEventHandler collectionChanged = this.CollectionChanged;
          if (collectionChanged != null)
              foreach (NotifyCollectionChangedEventHandler nh in collectionChanged.GetInvocationList())
              {
                  DispatcherObject dispObj = nh.Target as DispatcherObject;
                  if (dispObj != null)
                  {
                      Dispatcher dispatcher = dispObj.Dispatcher;
                      if (dispatcher != null &amp;&amp; !dispatcher.CheckAccess())
                      {
                          NotifyCollectionChangedEventHandler nh1 = nh;
                          dispatcher.BeginInvoke(
                              (Action) (() =&gt; nh1.Invoke(this,
                                                         new NotifyCollectionChangedEventArgs(
                                                             NotifyCollectionChangedAction.Reset))),
                              DispatcherPriority.DataBind);
                          continue;
                      }
                  }
                  nh.Invoke(this, e);
              }
      }
  }
  }
  </code></pre>
  
  <p>Please note, I can't translate this class to VB due to requiring an Event Override.
  Another variation I've tried, but falls foul of thread ownership again. The two collectionviews thing isn't yielding to a solution: I don't know if it's because the underlying collection isn't good for it or whether in reality it wasn't meant to work that way. I get close but no cigar.</p>
  
  <pre><code> Dim CarePlanList = Task.Run(Function() CarePlanSet.CarePlanList)
      Dim rcpdList = Task.Run(Function() rcpdSet.rcpdList)
  
      Dim tasks() As Task = {CarePlanList, rcpdList}
      Dim t = New TaskFactory
      Await t.ContinueWhenAll(tasks, Sub()
                                         carePlanSetViewSource.Source = CarePlanList
                                         rcpdSetViewSource.Source = rcpdList
                                     End Sub)
  </code></pre>
  
  <p>I found a way to do it, based on a combination of feedback and research this morning. Building the two collectionviews asynchronously itself is somewhat impractical given the STAThread model of WPF. However, merely ensuring one HAS completed and shifting some of the async out of one entity class has made this plausible.</p>
  
  <p>Instead I fire off the first task, who's underlying class does build it's data with its own Async method. Then test to see if it has completed before allowing the second collectionview to be fired off. This way I don't need to worry about context or dispatcherobjects. The second collection does not use any async.</p>
  
  <pre><code>    Dim personList = Task(Of List(Of person)).Run(Function() personSet.personList)
      Dim contactList = Task(Of ObservableCollectionEx(Of contact)).Run(Function() contactSet.contactList)
  
      contactSetViewSource.Source = contactList.Result
      If contactList.IsCompleted Then personSetViewSource.Source = personList.Result
  </code></pre>
  
  <p>This is an experimental project for concept research really. As it happens, the idea I'd want two such lists built this way isn't as useful as all that but I do see where being able to compose a data heavy interface asynchronously could be handy.</p>