监听系统开关变化

// 转屏开关
/**
     * Content observer which listens for system auto-rotate setting changes, and enables/disables
     * the launcher rotation setting accordingly.
     */
private static class SystemDisplayRotationLockObserver extends SettingsObserver.System {

        private final Preference mRotationPref;

        public SystemDisplayRotationLockObserver(
                Preference rotationPref, ContentResolver resolver) {
            super(resolver);
            mRotationPref = rotationPref;
        }

        @Override
        public void onSettingChanged(boolean enabled) {
            mRotationPref.setEnabled(enabled);
            mRotationPref.setSummary(enabled
                    ? R.string.allow_rotation_desc : R.string.allow_rotation_blocked_desc);
        }
    }