Don't add duplicate Threads to Thread list

This happens when coming back to the MainPage

Author: golf1052

Signal-Windows/ViewModels/MainPageViewModel.cs

@@ -65,6 +65,14 @@ public bool ThreadListAlignRight
 
         public void AddThread(SignalConversation contact)
         {
+            // only add a contact to Threads if it isn't already there
+            foreach (var thread in Threads)
+            {
+                if (thread.ThreadId == contact.ThreadId)
+                {
+                    return;
+                }
+            }
             Threads.Add(contact);
             ThreadsDictionary[contact.ThreadId] = contact;
         }
@@ -186,6 +194,12 @@ await Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatch
             Debug.WriteLine("Init lock released");
         }
 
+        public async Task OnNavigatingFrom()
+        {
+            SelectedThread = null;
+            View.Thread.DisposeCurrentThread();
+        }
+
         public async Task Shutdown()
         {
             Running = false;

Signal-Windows/Views/MainPage.xaml.cs

@@ -93,6 +93,13 @@ protected override async void OnNavigatedTo(NavigationEventArgs e)
             await Vm.Init();
         }
 
+        protected override async void OnNavigatingFrom(NavigatingCancelEventArgs e)
+        {
+            base.OnNavigatingFrom(e);
+            ContactsList.SelectedItem = null;
+            await Vm.OnNavigatingFrom();
+        }
+
         private void Frame_SizeChanged(object sender, SizeChangedEventArgs e)
         {
             var oldStyle = Utils.GetViewStyle(e.PreviousSize);