Hide "Changes made by your organization's admin" when empty

The admin of a manged device can take a number actions that will be
listed in the "Changes made by your organization's admin" section of
Settings. If the admin has not taken any such actions, the section
will be empty and should be hidden. This is accomplished by having a
PreferenceController for the section that observes the state of the
PreferenceControllers inside it.

Bug: 35912953
Test: m RunSettingsRoboTests

Change-Id: Ia95754493ee6c5a19b4aa9731fd56fd558e61849

src/com/android/settings/core/DynamicAvailabilityPreferenceController.java

@@ -29,6 +29,7 @@ public abstract class DynamicAvailabilityPreferenceController extends Preference
 
     private Preference mPreference;
     private PreferenceScreen mScreen;
+    private PreferenceAvailabilityObserver mAvailabilityObserver = null;
 
     public DynamicAvailabilityPreferenceController(Context context, Lifecycle lifecycle) {
         super(context);
@@ -37,6 +38,14 @@ public abstract class DynamicAvailabilityPreferenceController extends Preference
         }
     }
 
+    public void setAvailabilityObserver(PreferenceAvailabilityObserver observer) {
+        mAvailabilityObserver = observer;
+    }
+
+    public PreferenceAvailabilityObserver getAvailabilityObserver() {
+        return mAvailabilityObserver;
+    }
+
     @Override
     public void displayPreference(PreferenceScreen screen) {
         mScreen = screen;
@@ -56,4 +65,10 @@ public abstract class DynamicAvailabilityPreferenceController extends Preference
             mScreen.addPreference(mPreference);
         }
     }
+
+    protected void notifyOnAvailabilityUpdate(boolean available) {
+        if (mAvailabilityObserver != null) {
+            mAvailabilityObserver.onPreferenceAvailabilityUpdated(getPreferenceKey(), available);
+        }
+    }
 }

src/com/android/settings/core/PreferenceAvailabilityObserver.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2017 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.core;
+
+/**
+ * @deprecated This interface allows a {@link android.support.v7.preference.PreferenceGroup}'s
+ * controller to observe the availability of the {@link android.support.v7.preference.Preference}s
+ * inside it, hiding the group when all preferences become unavailable. In the future,
+ * {@link android.support.v7.preference.PreferenceGroup} will have native support for that
+ * functionality, removing the need for this interface.
+ */
+public interface PreferenceAvailabilityObserver {
+
+    /**
+     * Notifies the observer that the availability of the preference identified by {@code key} has
+     * been updated.
+     */
+    void onPreferenceAvailabilityUpdated(String key, boolean available);
+}