[Windows] Fix system theme integration. (flutter#35902)

The flutter#35019 didn't merge SettingsPluginWin32's constructor and destructor. This PR adds them and fix SettingsPlugin to re-enable it to watch the theme changes.

This PR is part of flutter/flutter#110700.

No changes in the flutter/tests repo.

Author: moko256

shell/platform/windows/settings_plugin.cc

@@ -36,7 +36,9 @@ SettingsPlugin::SettingsPlugin(BinaryMessenger* messenger,
           &JsonMessageCodec::GetInstance())),
       task_runner_(task_runner) {}
 
-SettingsPlugin::~SettingsPlugin() = default;
+SettingsPlugin::~SettingsPlugin() {
+  StopWatching();
+}
 
 void SettingsPlugin::SendSettings() {
   rapidjson::Document settings(rapidjson::kObjectType);
@@ -55,6 +57,12 @@ void SettingsPlugin::SendSettings() {
 }
 
 void SettingsPlugin::StartWatching() {
+  RegOpenKeyEx(HKEY_CURRENT_USER, kGetPreferredBrightnessRegKey,
+               RRF_RT_REG_DWORD, KEY_NOTIFY, &preferred_brightness_reg_hkey_);
+  RegOpenKeyEx(HKEY_CURRENT_USER, kGetTextScaleFactorRegKey, RRF_RT_REG_DWORD,
+               KEY_NOTIFY, &text_scale_factor_reg_hkey_);
+
+  // Start watching when the keys exist.
   if (preferred_brightness_reg_hkey_ != nullptr) {
     WatchPreferredBrightnessChanged();
   }
@@ -66,6 +74,13 @@ void SettingsPlugin::StartWatching() {
 void SettingsPlugin::StopWatching() {
   preferred_brightness_changed_watcher_ = nullptr;
   text_scale_factor_changed_watcher_ = nullptr;
+
+  if (preferred_brightness_reg_hkey_ != nullptr) {
+    RegCloseKey(preferred_brightness_reg_hkey_);
+  }
+  if (text_scale_factor_reg_hkey_ != nullptr) {
+    RegCloseKey(text_scale_factor_reg_hkey_);
+  }
 }
 
 bool SettingsPlugin::GetAlwaysUse24HourFormat() {

shell/platform/windows/settings_plugin.h

@@ -49,12 +49,15 @@ class SettingsPlugin {
   // Returns the user-preferred brightness.
   virtual PlatformBrightness GetPreferredBrightness();
 
+  // Starts watching brightness changes.
+  virtual void WatchPreferredBrightnessChanged();
+
+  // Starts watching text scale factor changes.
+  virtual void WatchTextScaleFactorChanged();
+
  private:
   std::unique_ptr<BasicMessageChannel<rapidjson::Document>> channel_;
 
-  void WatchPreferredBrightnessChanged();
-  void WatchTextScaleFactorChanged();
-
   HKEY preferred_brightness_reg_hkey_ = nullptr;
   HKEY text_scale_factor_reg_hkey_ = nullptr;
 

shell/platform/windows/settings_plugin_unittests.cc

@@ -22,12 +22,12 @@ class MockSettingsPlugin : public SettingsPlugin {
   virtual ~MockSettingsPlugin() = default;
 
   // |SettingsPlugin|
-  MOCK_METHOD0(StartWatching, void());
-  MOCK_METHOD0(StopWatching, void());
-
   MOCK_METHOD0(GetAlwaysUse24HourFormat, bool());
   MOCK_METHOD0(GetTextScaleFactor, float());
   MOCK_METHOD0(GetPreferredBrightness, PlatformBrightness());
+
+  MOCK_METHOD0(WatchPreferredBrightnessChanged, void());
+  MOCK_METHOD0(WatchTextScaleFactorChanged, void());
 };
 
 }  // namespace
@@ -58,5 +58,17 @@ TEST(SettingsPluginTest, SendSettingsGetsSettings) {
   settings_plugin.SendSettings();
 }
 
+TEST(SettingsPluginTest, StartWatchingStartsWatchingChanges) {
+  TestBinaryMessenger messenger([](const std::string& channel,
+                                   const uint8_t* message, size_t message_size,
+                                   BinaryReply reply) {});
+  ::testing::NiceMock<MockSettingsPlugin> settings_plugin(&messenger, nullptr);
+
+  EXPECT_CALL(settings_plugin, WatchPreferredBrightnessChanged).Times(1);
+  EXPECT_CALL(settings_plugin, WatchTextScaleFactorChanged).Times(1);
+
+  settings_plugin.StartWatching();
+}
+
 }  // namespace testing
 }  // namespace flutter