Fix: 修复 macOS 下主题模式「跟随系统设置」失效

HMCL/src/main/java/org/jackhuang/hmcl/theme/Themes.java

@@ -466,6 +466,16 @@ public static Brightness getCurrentBrightness() {
 
     /// Returns the brightness requested by the current system or platform settings.
     private static Brightness getAutomaticBrightness() {
+        // On macOS the launcher pins the application appearance (see #applyNativeDarkMode), and JavaFX derives its
+        // color scheme from NSApp.effectiveAppearance. Reading FXUtils.DARK_MODE here would therefore read back the
+        // brightness this launcher itself applied, so the system setting is read directly instead.
+        if (OperatingSystem.CURRENT_OS == OperatingSystem.MACOS && MacOSNativeUtils.isSupported()) {
+            @Nullable Boolean systemDarkMode = MacOSNativeUtils.isSystemInDarkMode();
+            if (systemDarkMode != null) {
+                return systemDarkMode ? Brightness.DARK : Brightness.LIGHT;
+            }
+        }
+
         if (FXUtils.DARK_MODE != null) {
             return FXUtils.DARK_MODE.get() ? Brightness.DARK : Brightness.LIGHT;
         }
@@ -1151,13 +1161,32 @@ public void handle(WindowEvent event) {
                 });
             }
         } else if (OperatingSystem.CURRENT_OS == OperatingSystem.MACOS && MacOSNativeUtils.isSupported()) {
-            MacOSNativeUtils.setAppearance(darkModeProperty().get());
+            applyMacOSAppearance(darkModeProperty().get());
 
-            ChangeListener<Boolean> listener = FXUtils.onWeakChange(Themes.darkModeProperty(), MacOSNativeUtils::setAppearance);
+            ChangeListener<Boolean> listener = FXUtils.onWeakChange(Themes.darkModeProperty(), Themes::applyMacOSAppearance);
             stage.getProperties().put("Themes.applyNativeDarkMode.listener", listener);
         }
     }
 
+    /// Applies the launcher brightness to the macOS application appearance.
+    ///
+    /// Setting an explicit appearance is what makes native windows owned by the application - notably the file
+    /// chooser - follow the launcher brightness instead of the system one. It has a cost: while an appearance is
+    /// pinned, `NSApp.effectiveAppearance` no longer reports the system appearance, so JavaFX stops reporting
+    /// system color scheme changes.
+    ///
+    /// The appearance is therefore only pinned while the launcher brightness actually differs from the system
+    /// brightness. When they agree - which is the case whenever the brightness mode follows the system - the
+    /// appearance is cleared, so the system appearance is inherited and JavaFX keeps observing system changes.
+    private static void applyMacOSAppearance(boolean dark) {
+        @Nullable Boolean systemDarkMode = MacOSNativeUtils.isSystemInDarkMode();
+        if (systemDarkMode != null && systemDarkMode == dark) {
+            MacOSNativeUtils.clearAppearance();
+        } else {
+            MacOSNativeUtils.setAppearance(dark);
+        }
+    }
+
     /// Prevents instantiation.
     private Themes() {
     }

HMCL/src/main/java/org/jackhuang/hmcl/ui/MacOSNativeUtils.java

@@ -96,6 +96,63 @@ public static void setAppearance(boolean dark, boolean highContrast) {
         }
     }
 
+    /// Clears the explicit application appearance, so that the application inherits the system appearance again.
+    ///
+    /// While an explicit appearance is set, `NSApp.effectiveAppearance` reports that appearance rather than the
+    /// system one. JavaFX derives [javafx.application.Platform.Preferences#colorSchemeProperty()] from
+    /// `effectiveAppearance`, so leaving an appearance pinned makes the reported color scheme follow the launcher
+    /// instead of the system.
+    public static void clearAppearance() {
+        if (nsApp == null) return;
+
+        try {
+            var objc = ObjectiveCRuntime.INSTANCE;
+            // A null Pointer maps to Objective-C nil, which resets the appearance to inherited.
+            objc.objc_msgSend(nsApp, objc.sel_registerName("setAppearance:"), (Pointer) null);
+        } catch (Throwable t) {
+            LOG.warning("Failed to clear macOS appearance", t);
+        }
+    }
+
+    /// Reads whether the system is currently using dark mode, independently of the application appearance.
+    ///
+    /// This reads the `AppleInterfaceStyle` user default, which reflects the system setting and is unaffected by
+    /// [#setAppearance(boolean)]. It must not be derived from `effectiveAppearance` or from the JavaFX color
+    /// scheme, because both report the pinned application appearance once one has been set.
+    ///
+    /// @return whether the system is in dark mode, or `null` if it could not be determined
+    public static @Nullable Boolean isSystemInDarkMode() {
+        if (nsApp == null) return null;
+
+        try {
+            var objc = ObjectiveCRuntime.INSTANCE;
+
+            @Nullable Pointer userDefaults = objc.objc_getClass("NSUserDefaults");
+            if (isNull(userDefaults)) return null;
+
+            @Nullable Pointer defaults = objc.objc_msgSend(userDefaults, objc.sel_registerName("standardUserDefaults"));
+            if (isNull(defaults)) return null;
+
+            @Nullable Pointer nsString = objc.objc_getClass("NSString");
+            if (isNull(nsString)) return null;
+
+            @Nullable Pointer key = objc.objc_msgSend(nsString, objc.sel_registerName("stringWithUTF8String:"), "AppleInterfaceStyle");
+            if (isNull(key)) return null;
+
+            @Nullable Pointer value = objc.objc_msgSend(defaults, objc.sel_registerName("stringForKey:"), key);
+            // The key is absent in light mode.
+            if (isNull(value)) return Boolean.FALSE;
+
+            @Nullable Pointer utf8 = objc.objc_msgSend(value, objc.sel_registerName("UTF8String"));
+            if (isNull(utf8)) return null;
+
+            return "Dark".equalsIgnoreCase(utf8.getString(0));
+        } catch (Throwable t) {
+            LOG.warning("Failed to read macOS system appearance", t);
+            return null;
+        }
+    }
+
     private MacOSNativeUtils() {
     }
 }