Make TrackingCollection refreshable

Author: shana

src/GitHub.Exports.Reactive/Collections/TrackingCollection.cs

@@ -88,6 +88,7 @@ public TrackingCollection(Func<T, T, int> comparer = null, Func<T, int, IList<T>
             this.filter = filter;
         }
 
+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
         public TrackingCollection(IObservable<T> source,
             Func<T, T, int> comparer = null,
             Func<T, int, IList<T>, bool> filter = null,
@@ -109,6 +110,10 @@ public IObservable<T> Listen(IObservable<T> obs)
             if (disposed)
                 throw new ObjectDisposedException("TrackingCollection");
 
+            disposables.Clear();
+            while (!queue.IsEmpty)
+                GetFromQueue();
+
             sourceQueue = obs
                 .Do(data => queue.Enqueue(new ActionData(data)));