Avoid crash if settings cannot be deserialized

Author: Maxhy

WpfApp/AboutWindow.xaml.cs

@@ -73,15 +73,15 @@ private void BtnCheckUpdate_Click(object sender, RoutedEventArgs e)
         private void Window_Loaded(object sender, RoutedEventArgs e)
         {
             AutoUpdateToggleButton.IsChecked = true;
-            if (AppSettings.GetSingletonInstance().IsAutoUpdateEnabled)
+            if ((AppSettings.GetSingletonInstance()?.IsAutoUpdateEnabled).GetValueOrDefault(false))
             {
                 CheckUpdate();
             }
         }
 
         private void AutoUpdateToggleButton_Click(object sender, RoutedEventArgs e)
         {
-            var settings = AppSettings.GetSingletonInstance();
+            var settings = AppSettings.GetSingletonInstance() ?? new AppSettings();
             settings.IsAutoUpdateEnabled = AutoUpdateToggleButton.IsChecked.GetValueOrDefault(false);
             if (settings.IsAutoUpdateEnabled)
             {

WpfApp/Domain/AboutWindowViewModel.cs

@@ -34,7 +34,7 @@ public AboutWindowViewModel()
         {
             GetInfoFromAssembly();
 
-            _settings = AppSettings.GetSingletonInstance();
+            _settings = AppSettings.GetSingletonInstance() ?? new AppSettings();
             _autoUpdate = new AutoUpdate();
 
             Libraries = new ObservableCollection<Library>(new[]

WpfApp/Domain/MainWindowViewModel.cs

@@ -39,7 +39,7 @@ public MainWindowViewModel(ISnackbarMessageQueue snackbarMessageQueue)
                         lang = "en-US";
                     }
 
-                    var settings = UserAppSettings.GetSingletonInstance();
+                    var settings = UserAppSettings.GetSingletonInstance() ?? new UserAppSettings();
                     settings.Language = lang;
                     settings.SaveToFile();
 
@@ -135,20 +135,20 @@ public static void ModifyAndSaveTheme(bool isDarkTheme)
         {
             ModifyTheme(isDarkTheme);
 
-            var settings = UserAppSettings.GetSingletonInstance();
+            var settings = UserAppSettings.GetSingletonInstance() ?? new UserAppSettings();
             settings.UseDarkTheme = isDarkTheme;
             settings.SaveToFile();
         }
 
         public void InitFromSettings()
         {
             var userSettings = UserAppSettings.GetSingletonInstance();
-            if (userSettings.UseDarkTheme)
+            if (userSettings != null && userSettings.UseDarkTheme)
             {
                 IsDarkMode = userSettings.UseDarkTheme;
             }
             var settings = AppSettings.GetSingletonInstance();
-            if (settings.IsAutoUpdateEnabled)
+            if (settings != null && settings.IsAutoUpdateEnabled)
             {
                 Application.Current.Dispatcher.BeginInvoke(async () =>
                 {