[gnome-tweak-tool] widgets: Enable Dark Theme for gtk4 too

[Jeremy Bicha <jbicha src gnome org>]

commit 62c0f53bedeafec5255df1743b638bb48cfd24cb
Author: Jeremy Bicha <jbicha ubuntu com>
Date:   Mon May 29 18:50:06 2017 -0400

    widgets: Enable Dark Theme for gtk4 too
    
    https://bugzilla.gnome.org/show_bug.cgi?id=780915

 gtweak/gtksettings.py |    5 ++---
 gtweak/widgets.py     |    9 ++++++---
 2 files changed, 8 insertions(+), 6 deletions(-)
---
diff --git a/gtweak/gtksettings.py b/gtweak/gtksettings.py
index bcec9f1..8d10f2e 100644
--- a/gtweak/gtksettings.py
+++ b/gtweak/gtksettings.py
@@ -26,11 +26,10 @@ SETTINGS_GROUP_NAME = "Settings"
 
 LOG = logging.getLogger(__name__)
 
-@gtweak.utils.singleton
 class GtkSettingsManager:
-    def __init__(self):
+    def __init__(self, version):
         self._path = os.path.join(GLib.get_user_config_dir(),
-                                  "gtk-3.0",
+                                  "gtk-" + version,
                                   "settings.ini")
     def _get_keyfile(self):
         keyfile = None
diff --git a/gtweak/widgets.py b/gtweak/widgets.py
index 8422880..b3c43c7 100644
--- a/gtweak/widgets.py
+++ b/gtweak/widgets.py
@@ -501,10 +501,11 @@ class DarkThemeSwitcher(Gtk.Box, Tweak):
                        _("Enable the dark theme hint for all the applications in the session"),
                        **options)
 
-        self._gtksettings = GtkSettingsManager()
+        self._gtksettings3 = GtkSettingsManager('3.0')
+        self._gtksettings4 = GtkSettingsManager('4.0')
 
         w = Gtk.Switch()
-        w.set_active(self._gtksettings.get_integer("gtk-application-prefer-dark-theme"))
+        w.set_active(self._gtksettings3.get_integer("gtk-application-prefer-dark-theme"))
                
         title = _("Global Dark Theme")
         description = _("Applications need to be restarted for this change to take place.")
@@ -531,7 +532,9 @@ class DarkThemeSwitcher(Gtk.Box, Tweak):
         active = switch.get_active()
 
         try:
-            self._gtksettings.set_integer("gtk-application-prefer-dark-theme",
+            self._gtksettings3.set_integer("gtk-application-prefer-dark-theme",
+                                          active)
+            self._gtksettings4.set_integer("gtk-application-prefer-dark-theme",
                                           active)
         except:
             self.notify_information(_("Error writing setting"))