Implement the main switch of notifications on lock screen

Add the ability of controlling whether to show notifs on the lock
screen (secure setting: lock_screen_show_notifications) to the new
lock screen notification settings page main switch. This switch also
listens to the change of lock_screen_show_notifications to update
its status in case of other places change the value.

Bug: 367455695
Flag: com.android.server.notification.notification_lock_screen_settings
Test: atest LockScreenNotificationsPreferenceControllerTest
Change-Id: Id598d508ac383563a0d9413578251eb22ed4ca90

res/xml/lock_screen_notifications_settings.xml

@@ -20,5 +20,9 @@
     xmlns:settings="http://schemas.android.com/apk/res-auto"
     xmlns:app="http://schemas.android.com/apk/res-auto">
 
+    <com.android.settingslib.widget.MainSwitchPreference
+        android:key="lock_screen_notification_global_pref"
+        android:title="@string/switch_on_text"
+        settings:controller="com.android.settings.notification.LockScreenNotificationsGlobalPreferenceController"/>
 
 </PreferenceScreen>

src/com/android/settings/notification/LockScreenNotificationsGlobalPreferenceController.java

@@ -0,0 +1,117 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.notification;
+
+import android.content.ContentResolver;
+import android.content.Context;
+import android.database.ContentObserver;
+import android.net.Uri;
+import android.os.Handler;
+import android.os.Looper;
+import android.provider.Settings;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.lifecycle.Lifecycle;
+import androidx.lifecycle.LifecycleEventObserver;
+import androidx.lifecycle.LifecycleOwner;
+import androidx.preference.Preference;
+import androidx.preference.PreferenceScreen;
+
+import com.android.server.notification.Flags;
+import com.android.settings.widget.SettingsMainSwitchPreferenceController;
+
+public class LockScreenNotificationsGlobalPreferenceController
+        extends SettingsMainSwitchPreferenceController
+        implements LifecycleEventObserver {
+
+    public static final int ON = 1;
+    public static final int OFF = 0;
+    private final ContentResolver mContentResolver;
+    private final ContentObserver mContentObserver;
+    @Nullable private Preference mPreference;
+
+
+    public LockScreenNotificationsGlobalPreferenceController(
+            @NonNull Context context,
+            @NonNull String preferenceKey
+    ) {
+        super(context, preferenceKey);
+        mContentResolver = context.getContentResolver();
+        mContentObserver = new ContentObserver(new Handler(Looper.getMainLooper())) {
+            @Override
+            public void onChange(boolean selfChange, @Nullable Uri uri) {
+                if (mPreference == null) return;
+                updateState(mPreference);
+            }
+        };
+    }
+
+    @Override
+    public void displayPreference(@NonNull PreferenceScreen screen) {
+        super.displayPreference(screen);
+        mPreference = screen.findPreference(getPreferenceKey());
+    }
+
+    @Override
+    public void updateState(@NonNull Preference preference) {
+        super.updateState(preference);
+        setChecked(lockScreenShowNotifications());
+    }
+
+    @Override
+    public int getAvailabilityStatus() {
+        // TODO: b/367455695 - remove this when the feature flag is removed!
+        return Flags.notificationLockScreenSettings() ? AVAILABLE : CONDITIONALLY_UNAVAILABLE;
+    }
+
+    @Override
+    public boolean isChecked() {
+        return lockScreenShowNotifications();
+    }
+
+    private boolean lockScreenShowNotifications() {
+        return Settings.Secure.getInt(mContext.getContentResolver(),
+                Settings.Secure.LOCK_SCREEN_SHOW_NOTIFICATIONS, OFF) == ON;
+    }
+
+    @Override
+    public boolean setChecked(boolean isChecked) {
+        return Settings.Secure.putInt(mContext.getContentResolver(),
+                Settings.Secure.LOCK_SCREEN_SHOW_NOTIFICATIONS, (isChecked ? ON : OFF));
+    }
+
+    @Override
+    public int getSliceHighlightMenuRes() {
+        // not needed since it's not sliceable
+        return NO_RES;
+    }
+
+    @Override
+    public void onStateChanged(@NonNull LifecycleOwner lifecycleOwner,
+            @NonNull Lifecycle.Event event) {
+        if (event == Lifecycle.Event.ON_RESUME) {
+            mContentResolver.registerContentObserver(
+                    Settings.Secure.getUriFor(Settings.Secure.LOCK_SCREEN_SHOW_NOTIFICATIONS),
+                    /* notifyForDescendants= */ false,
+                    mContentObserver
+            );
+        } else {
+            mContentResolver.unregisterContentObserver(mContentObserver);
+        }
+    }
+}