Added ChangeThemeMode

@@ -599,6 +599,10 @@ class Get {
     _get._getController.setTheme(theme);
   }
 
+  Get.changeThemeMode(ThemeMode themeMode) {
+    Get()._getController.setThemeMode(themeMode);
+  }
+
   Get.restartApp() {
     _get._getController.restartApp();
   }

@@ -6,12 +6,18 @@ class GetMaterialController extends GetController {
   ParseRoute parse = ParseRoute();
   Key key = UniqueKey();
   ThemeData theme;
+  ThemeMode themeMode;
 
   void setTheme(ThemeData value) {
     theme = value;
     update(this);
   }
 
+  void setThemeMode(ThemeMode value) {
+    themeMode = value;
+    update(this);
+  }
+
   void restartApp() {
     key = UniqueKey();
     update(this);

@@ -213,7 +213,7 @@ class GetMaterialApp extends StatelessWidget {
             color: color,
             theme: _.theme ?? theme ?? ThemeData.fallback(),
             darkTheme: darkTheme,
-            themeMode: themeMode ?? ThemeMode.system,
+            themeMode: _.themeMode ?? themeMode ?? ThemeMode.system,
             locale: locale,
             localizationsDelegates: localizationsDelegates,
             localeListResolutionCallback: localeListResolutionCallback,