Fix Windows' try_theme returning Theme::Dark when new theme is light (#1861)

CHANGELOG.md

@@ -9,6 +9,7 @@
 - On Android, unimplemented events are marked as unhandled on the native event loop.
 - On Windows, added `WindowBuilderExtWindows::with_menu` to set a custom menu at window creation time.
 - On Android, bump `ndk` and `ndk-glue` to 0.3: use predefined constants for event `ident`.
+- On Windows, fixed `WindowEvent::ThemeChanged` not properly firing and fixed `Window::theme` returning the wrong theme.
 - On Web, added support for `DeviceEvent::MouseMotion` to listen for relative mouse movements.
 
 # 0.24.0 (2020-12-09)

src/platform_impl/windows/dark_mode.rs

@@ -81,16 +81,20 @@ pub fn try_theme(hwnd: HWND, preferred_theme: Option<Theme>) -> Theme {
             None => should_use_dark_mode(),
         };
 
-        let theme_name = if is_dark_mode {
-            DARK_THEME_NAME.as_ptr()
+        let theme = if is_dark_mode {
+            Theme::Dark
         } else {
-            LIGHT_THEME_NAME.as_ptr()
+            Theme::Light
+        };
+        let theme_name = match theme {
+            Theme::Dark => DARK_THEME_NAME.as_ptr(),
+            Theme::Light => LIGHT_THEME_NAME.as_ptr(),
         };
 
         let status = unsafe { uxtheme::SetWindowTheme(hwnd, theme_name as _, std::ptr::null()) };
 
         if status == S_OK && set_dark_mode_for_window(hwnd, is_dark_mode) {
-            return Theme::Dark;
+            return theme;
         }
     }