Try to avoid recurion and comment

Author: VictoriousRaptor

Flow.Launcher/SettingWindow.xaml.cs

@@ -519,6 +519,10 @@ private void PreviewClockAndDate(object sender, RoutedEventArgs e)
         {
             if (DateFormat != null && TimeFormat != null)
             {
+                if (DateFormat.SelectedIndex == -1 || TimeFormat.SelectedIndex == -1)
+                {
+                    return;
+                }
                 viewModel.UpdateDateTimeDisplayList(DateFormat.SelectedIndex, TimeFormat.SelectedIndex);
                 DateFormat.Items.Refresh();
                 TimeFormat.Items.Refresh(); // selected = -1

Flow.Launcher/ViewModel/SettingWindowViewModel.cs

@@ -52,7 +52,7 @@ public SettingWindowViewModel(Updater updater, IPortable portable)
             int tmp = 0;
             TimeFormatIndex = (tmp = TimeFormatList.FindIndex(x => x.Equals(Settings.TimeFormat))) >= 0 ? tmp : 0;
             DateFormatIndex = (tmp = DateFormatList.FindIndex(x => x.Equals(Settings.DateFormat))) >= 0 ? tmp : 0;
-
+            // TODO: CurrentCulture may equal to settings.language when this is constructed
             TimeFormatDisplayList = TimeFormatList.Select(x => DateTime.Now.ToString(x, CultureInfo.CurrentCulture)).ToList();
             DateFormatDisplayList = DateFormatList.Select(x => DateTime.Now.ToString(x, CultureInfo.CurrentCulture)).ToList();
             UpdateSettingsDateTimeFormat();  // just in case something wrong
@@ -492,8 +492,6 @@ public void UpdateSettingsDateTimeFormat()
 
         public void UpdateDateTimeDisplayList(int dateIndex, int timeIndex)
         {
-            if (dateIndex == -1 || timeIndex == -1) 
-                return;
             DateFormatIndex = dateIndex;
             TimeFormatIndex = timeIndex;