Optimize FluentTheme updating

ios/FluentUI.Demo/FluentUI.Demo/BrandedSwitch.swift

@@ -10,16 +10,15 @@ class BrandedSwitch: UISwitch {
     override init(frame: CGRect) {
         super.init(frame: frame)
 
-        NotificationCenter.default.addObserver(forName: .didChangeTheme,
-                                               object: nil,
-                                               queue: nil) { [weak self] notification in
+        notificationObserver = NotificationCenter.default.addObserver(forName: .didChangeTheme,
+                                                                      object: nil,
+                                                                      queue: nil) { [weak self] notification in
             guard let strongSelf = self,
-                  let themeView = notification.object as? UIView,
-                  strongSelf.isDescendant(of: themeView)
+                  FluentTheme.isApplicableThemeChange(notification, for: strongSelf)
             else {
                 return
             }
-            strongSelf.onTintColor = themeView.fluentTheme.color(.brandForeground1)
+            strongSelf.onTintColor = strongSelf.fluentTheme.color(.brandForeground1)
         }
     }
 
@@ -34,4 +33,7 @@ class BrandedSwitch: UISwitch {
         }
         onTintColor = newWindow.fluentTheme.color(.brandForeground1)
     }
+
+    /// Stores the notification handler for .didChangeTheme notifications.
+    private var notificationObserver: NSObjectProtocol?
 }

ios/FluentUI.Demo/FluentUI.Demo/ColoredPillBackgroundView.swift

@@ -29,7 +29,7 @@ class ColoredPillBackgroundView: UIView {
     }
 
     @objc func themeDidChange(_ notification: Notification) {
-        guard let themeView = notification.object as? UIView, self.isDescendant(of: themeView) else {
+        guard FluentTheme.isApplicableThemeChange(notification, for: self) else {
             return
         }
         updateBackgroundColor()

ios/FluentUI.Demo/FluentUI.Demo/DemoListViewController.swift

@@ -30,7 +30,7 @@ class DemoListViewController: DemoTableViewController {
     func updateColorProviderFor(window: UIWindow, theme: DemoColorTheme) {
         self.theme = theme
         if let provider = self.provider {
-            FluentTheme.setSharedThemeColorProvider(provider)
+            window.setColorProvider(provider)
             let fluentTheme = self.view.fluentTheme
             let primaryColor = fluentTheme.color(.brandBackground1)
             FluentUIFramework.initializeAppearance(with: primaryColor, whenContainedInInstancesOf: [type(of: window)])

ios/FluentUI/Calendar/CalendarView.swift

@@ -61,7 +61,7 @@ class CalendarView: UIView {
     }
 
     @objc private func themeDidChange(_ notification: Notification) {
-        guard let themeView = notification.object as? UIView, self.isDescendant(of: themeView) else {
+        guard FluentTheme.isApplicableThemeChange(notification, for: self) else {
             return
         }
         updateCollectionViewBackgroundColor()

ios/FluentUI/Calendar/Views/CalendarViewWeekdayHeadingView.swift

@@ -37,7 +37,7 @@ class CalendarViewWeekdayHeadingView: UIView {
     }
 
     @objc private func themeDidChange(_ notification: Notification) {
-        guard let themeView = notification.object as? UIView, self.isDescendant(of: themeView) else {
+        guard FluentTheme.isApplicableThemeChange(notification, for: self) else {
             return
         }
         updateBackgroundColor()

ios/FluentUI/Core/ControlHostingView.swift

@@ -74,7 +74,7 @@ open class ControlHostingView: UIView {
     }
 
     @objc private func themeDidChange(_ notification: Notification) {
-        guard let themeView = notification.object as? UIView, self.isDescendant(of: themeView) else {
+        guard FluentTheme.isApplicableThemeChange(notification, for: self) else {
             return
         }
         updateRootView()

ios/FluentUI/Core/Theme/FluentTheme.swift

@@ -92,19 +92,33 @@ public class FluentTheme: NSObject, ObservableObject {
     @objc(sharedTheme)
     public internal(set) static var shared: FluentTheme = FluentThemeKey.defaultValue {
         didSet {
-            UIApplication.shared.connectedScenes
-                .compactMap {
-                    $0 as? UIWindowScene
-                }
-                .flatMap {
-                    $0.windows
-                }
-                .forEach { window in
-                    NotificationCenter.default.post(name: .didChangeTheme, object: window)
-                }
+            NotificationCenter.default.post(name: .didChangeTheme, object: nil)
         }
     }
 
+    /// Determines if a given `Notification` should cause an update for the given `UIView`.
+    ///
+    /// - Parameter notification: A `Notification` object that may be requesting a view update based on a theme change.
+    /// - Parameter view: The `UIView` instance that wants to determine whether to update.
+    ///
+    /// - Returns: `True` if the view should update, `false` otherwise.
+    @objc(isApplicableThemeChangeNotification:forView:)
+    public static func isApplicableThemeChange(_ notification: Notification,
+                                               for view: UIView) -> Bool {
+        // Do not update unless the notification's name is `.didChangeTheme`.
+        guard notification.name == .didChangeTheme else {
+            return false
+        }
+
+        // If there is no object, or it is not a UIView, we must assume that we need to update.
+        guard let themeView = notification.object as? UIView else {
+            return true
+        }
+
+        // If the object is a UIView, we only update if `view` is a descendant thereof.
+        return view.isDescendant(of: themeView)
+    }
+
     // Token storage
     let colorTokenSet: TokenSet<ColorToken, UIColor>
     let shadowTokenSet: TokenSet<ShadowToken, ShadowInfo>

ios/FluentUI/Core/Theme/Tokens/ControlTokenSet.swift

@@ -162,13 +162,12 @@ public class ControlTokenSet<T: TokenSetKey>: ObservableObject {
                                                                       object: nil,
                                                                       queue: nil) { [weak self, weak control] notification in
             guard let strongSelf = self,
-                  let themeView = notification.object as? UIView,
                   let control,
-                  control.isDescendant(of: themeView)
+                  FluentTheme.isApplicableThemeChange(notification, for: control)
             else {
                 return
             }
-            strongSelf.update(themeView.fluentTheme)
+            strongSelf.update(control.fluentTheme)
         }
     }
 

ios/FluentUI/Date Time Pickers/Date Picker/DatePickerController.swift

@@ -149,7 +149,7 @@ class DatePickerController: UIViewController, GenericDateTimePicker {
     }
 
     @objc private func themeDidChange(_ notification: Notification) {
-        guard let themeView = notification.object as? UIView, view.isDescendant(of: themeView) else {
+        guard FluentTheme.isApplicableThemeChange(notification, for: view) else {
             return
         }
         updateBackgroundColor()

ios/FluentUI/Date Time Pickers/Date Time Picker/DateTimePickerController.swift

@@ -115,7 +115,7 @@ class DateTimePickerController: UIViewController, GenericDateTimePicker {
     }
 
     @objc private func themeDidChange(_ notification: Notification) {
-        guard let themeView = notification.object as? UIView, view.isDescendant(of: themeView) else {
+        guard FluentTheme.isApplicableThemeChange(notification, for: view) else {
             return
         }
         updateBackgroundColor()

ios/FluentUI/Date Time Pickers/Date Time Picker/Views/DateTimePickerView.swift

@@ -89,7 +89,7 @@ class DateTimePickerView: UIControl {
     }
 
     @objc private func themeDidChange(_ notification: Notification) {
-        guard let themeView = notification.object as? UIView, self.isDescendant(of: themeView) else {
+        guard FluentTheme.isApplicableThemeChange(notification, for: self) else {
             return
         }
         updateBackgroundColor()

ios/FluentUI/People Picker/PersonaListView.swift

@@ -100,7 +100,7 @@ open class PersonaListView: UITableView {
     }
 
     @objc private func themeDidChange(_ notification: Notification) {
-        guard let themeView = notification.object as? UIView, self.isDescendant(of: themeView) else {
+        guard FluentTheme.isApplicableThemeChange(notification, for: self) else {
             return
         }
         updateBackgroundColor()

ios/FluentUI/Presenters/PageCardPresenterController.swift

@@ -76,7 +76,7 @@ open class PageCardPresenterController: UIViewController {
     }
 
     @objc private func themeDidChange(_ notification: Notification) {
-        guard let themeView = notification.object as? UIView, view.isDescendant(of: themeView) else {
+        guard FluentTheme.isApplicableThemeChange(notification, for: view) else {
             return
         }
         updatePageControlColors()