C#

BillWoodruff wrote:

I would ask Mads T. if I could

This type of CollectionView does not support changes to its SourceCollection from a thread different from the Dispatcher thread.

public class MainViewModel:BindableBase
   {

     //  ObservableCollection<string> MainCollection = new ObservableCollection<string>();

       #region "ctor"
       public MainViewModel()
       {

           Text = "1: Main UI thread on: " + Thread.CurrentThread.ManagedThreadId.ToString();
           TextCollection.Add("1: Main UI thread on: " + Thread.CurrentThread.ManagedThreadId.ToString());
           Task.Run(() => DoSomething(MethodCallback)).Await(CompletedCallback, ErrorCallback);
       }
       #endregion

       async Task DoSomething(Action<string> methodCallback)
       {
           await Task.Delay(1500);
           methodCallback?.Invoke("2: Task starts on thread: " + Thread.CurrentThread.ManagedThreadId.ToString());
           TextCollection.Add("2,5: Task starts on thread: " + Thread.CurrentThread.ManagedThreadId.ToString());
           await Task.Delay(1500);

           //throw new Exception("Aborted exception on thread " + Thread.CurrentThread.ManagedThreadId.ToString());

           methodCallback?.Invoke("3: Task runs on thread: " + Thread.CurrentThread.ManagedThreadId.ToString());
           await Task.Delay(1500);
       }

       #region "Variables"

       private ObservableCollection<string> _textCollection = new ObservableCollection<string>();
       public ObservableCollection<string> TextCollection
       {
           get { return _textCollection; }
           set { SetProperty(ref _textCollection, value); }
       }

       private string _text = "Default value";

       public string Text
       {
           get { return _text; }
           set
           {
               SetProperty(ref _text, value);
           }
       }
       #endregion

       #region "Callback methods"

       private void CompletedCallback()
       {
           Text = "4: Method completed called from thread: " + Thread.CurrentThread.ManagedThreadId.ToString();
           TextCollection.Add("4: Method completed called from thread: " + Thread.CurrentThread.ManagedThreadId.ToString());
       }

       private void MethodCallback(string message)
       {
           Text = message + Environment.NewLine +  "Task callback from thread: " + Thread.CurrentThread.ManagedThreadId.ToString();
           TextCollection.Add(message + Environment.NewLine + "Task callback from thread: " + Thread.CurrentThread.ManagedThreadId.ToString());
       }

       private void ErrorCallback(Exception ex)
       {
           Text = ex.Message;
       }
       #endregion
   }
   public static class TaskExtensions
   {
       public async static void Await(this Task task, Action completedCallback, Action<Exception> errorCallback)
       {
           try
           {
               await task;
               completedCallback?.Invoke();
           }
           catch (Exception ex)
           {
               errorCallback?.Invoke(ex);
           }
       }
   }

private object _TextCollectionLock = new object();

public MainViewModel()
{
    BindingOperations.EnableCollectionSynchronization(TextCollection, _TextCollectionLock);
    ...
}

Dave Kreskowiak wrote:

You have to create your own collection type that does the marshalling.