Fix common exceptions

Telegram/Common/MediaDeviceList.cs

@@ -103,7 +103,7 @@ public bool? HasValues
             {
                 lock (_cache)
                 {
-                    return _cache.Count > 0 ? true : _watcher.Status == DeviceWatcherStatus.EnumerationCompleted ? false : null;
+                    return _cache.Count > 0 ? true : _watcher?.Status == DeviceWatcherStatus.EnumerationCompleted ? false : null;
                 }
             }
         }

Telegram/Controls/ChatListListView.cs

@@ -185,7 +185,7 @@ void Continue(bool restore)
                 }
             }
 
-            if (_changingView || direction == CarouselDirection.None || !IsConnected || !PowerSavingPolicy.AreSmoothTransitionsEnabled)
+            if (_changingView || _tracker == null || direction == CarouselDirection.None || !IsConnected || !PowerSavingPolicy.AreSmoothTransitionsEnabled)
             {
                 Continue(true);
                 return;

Telegram/Controls/FileButton.cs

@@ -53,6 +53,12 @@ public partial class FileButton : GlyphHyperlinkButton
         public FileButton()
         {
             DefaultStyleKey = typeof(FileButton);
+            Connected += OnConnected;
+        }
+
+        private void OnConnected(object sender, RoutedEventArgs e)
+        {
+            // Used to enable FrameworkElementEx
         }
 
         public MessageContentState State => _state;
@@ -112,7 +118,7 @@ public double Progress
         {
             set
             {
-                if (_shouldEnqueueProgress)
+                if (_shouldEnqueueProgress || !IsConnected)
                 {
                     _enqueuedProgress = value;
                 }
@@ -240,7 +246,7 @@ private void OnGlyphChanged(string newValue, string oldValue, bool animate, stri
 
             _label.Text = newValue;
 
-            if (_hasContainer && (clearContainer || !animate) && this.IsConnected())
+            if (_hasContainer && (clearContainer || !animate) && IsConnected)
             {
                 _hasContainer = false;
                 ElementComposition.SetElementChildVisual(RootGrid, null);
@@ -370,7 +376,7 @@ private void OnDownloadingCompleted(object sender, CompositionBatchCompletedEven
         {
             try
             {
-                if (_state == MessageContentState.Downloading && this.IsConnected())
+                if (_state == MessageContentState.Downloading && IsConnected)
                 {
                     OnGlyphChanged(Icons.Cancel, Icons.ArrowDownload, true, Strings.AccActionCancelDownload, false);
                     InternalProgress = _enqueuedProgress;

Telegram/Controls/FrameworkElementEx.cs

@@ -662,4 +662,84 @@ private void OnChanged(object sender, RoutedEventArgs e)
             }
         }
     }
+
+    public partial class HyperlinkButtonEx : HyperlinkButton
+    {
+        private bool _loaded;
+        private bool _unloaded;
+
+        public bool IsConnected => _loaded;
+        public bool IsDisconnected => _unloaded;
+
+        private event RoutedEventHandler _connected;
+        public event RoutedEventHandler Connected
+        {
+            add
+            {
+                if (_connected == null && _disconnected == null)
+                {
+                    Loaded += OnChanged;
+                    Unloaded += OnChanged;
+                }
+
+                _connected += value;
+            }
+            remove
+            {
+                _connected -= value;
+
+                if (_connected == null && _disconnected == null)
+                {
+                    Loaded -= OnChanged;
+                    Unloaded -= OnChanged;
+                }
+            }
+        }
+
+        private event RoutedEventHandler _disconnected;
+        public event RoutedEventHandler Disconnected
+        {
+            add
+            {
+                if (_connected == null && _disconnected == null)
+                {
+                    Loaded += OnChanged;
+                    Unloaded += OnChanged;
+                }
+
+                _disconnected += value;
+            }
+            remove
+            {
+                _disconnected -= value;
+
+                if (_connected == null && _disconnected == null)
+                {
+                    Loaded -= OnChanged;
+                    Unloaded -= OnChanged;
+                }
+            }
+        }
+
+        private void OnChanged(object sender, RoutedEventArgs e)
+        {
+            // TODO: unfortunately FrameworkElement.Parent returns null
+            // whenever the control is a DataTemplate root or similar,
+            // hence we're forced to use VisualTreeHelper here, but I'm quite sure it's slower.
+
+            var parent = Parent ?? Windows.UI.Xaml.Media.VisualTreeHelper.GetParent(this);
+            if (parent != null && !_loaded)
+            {
+                _loaded = true;
+                _unloaded = false;
+                _connected?.Invoke(this, e);
+            }
+            else if (parent == null && _loaded)
+            {
+                _loaded = false;
+                _unloaded = true;
+                _disconnected?.Invoke(sender, e);
+            }
+        }
+    }
 }

Telegram/Controls/GlyphButton.cs

@@ -28,7 +28,7 @@ public string Glyph
         #endregion
     }
 
-    public partial class GlyphHyperlinkButton : HyperlinkButton
+    public partial class GlyphHyperlinkButton : HyperlinkButtonEx
     {
         public GlyphHyperlinkButton()
         {

Telegram/Services/ClientService.cs

@@ -657,7 +657,10 @@ private void UpdateTimeZones()
 
         public bool TryGetTimeZone(string timeZoneId, out TimeZone timeZone)
         {
-            return _timezones.TryGetValue(timeZoneId, out timeZone);
+            lock (_timezones)
+            {
+                return _timezones.TryGetValue(timeZoneId, out timeZone);
+            }
         }
 
         private void UpdateGreetingStickers()