feat(dark-mode): respect traitCollectionColorAppearanceChanged event

tns-core-modules/application/application.ios.ts

@@ -21,6 +21,7 @@ import {
     CLASS_PREFIX,
     getRootViewCssClasses,
     pushToRootViewCssClasses,
+    removeFromRootViewCssClasses,
     resetRootViewCssClasses
 } from "../css/system-classes";
 import { ios as iosView, View } from "../ui/core/view";
@@ -31,6 +32,12 @@ import { ios } from "../utils/utils";
 
 const IOS_PLATFORM = "ios";
 
+// TODO:
+const UI_STYLE_CSS_CLASSES = [
+    `${CLASS_PREFIX}light`,
+    `${CLASS_PREFIX}dark`
+];
+
 const getVisibleViewController = ios.getVisibleViewController;
 
 // NOTE: UIResponder with implementation of window - related to https://github.com/NativeScript/ios-runtime/issues/430
@@ -288,6 +295,26 @@ class IOSApplication implements IOSApplicationDefinition {
         }
 
         setupRootViewCssClasses(controller, rootView);
+
+        rootView.on(iosView.traitCollectionColorAppearanceChangedEvent, () => {
+
+            const newUserInterfaceStyle = controller.traitCollection.userInterfaceStyle;
+            const newUserInterfaceStyleValue = getUserInterfaceStyleValue(newUserInterfaceStyle);
+            const newUserInterfaceStyleCssClass = `${CLASS_PREFIX}${newUserInterfaceStyleValue}`;
+
+            if (!rootView.cssClasses.has(newUserInterfaceStyleCssClass)) {
+                const removeCssClass = (c: string) => {
+                    removeFromRootViewCssClasses(c);
+                    rootView.cssClasses.delete(c);
+                };
+
+                // TODO:
+                UI_STYLE_CSS_CLASSES.forEach(c => removeCssClass(c));
+                pushToRootViewCssClasses(newUserInterfaceStyleCssClass);
+                rootView.cssClasses.add(newUserInterfaceStyleCssClass);
+                rootView._onCssStateChange();
+            }
+        });
     }
 }
 
@@ -359,6 +386,7 @@ export function _start(entry?: string | NavigationEntry) {
                     }
 
                     setupRootViewCssClasses(controller, rootView);
+                    // TODO:
                     iosApp.notifyAppStarted();
                 }
             }