Add DynamicAvailabilityPreferenceController

This is a PreferenceController that correctly handles the case of
isAvailable() changing dynamically, while the Settings page containing
the preference in question is open.

Bug: 32692748
Test: m RunSettingsRoboTests

Change-Id: I95e22bbc7bdc17bacd2bf6b82fa5b535494d5bce

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

@@ -0,0 +1,59 @@
+/*
+ * 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;
+
+import android.content.Context;
+import android.support.v7.preference.Preference;
+import android.support.v7.preference.PreferenceScreen;
+
+import com.android.settings.core.lifecycle.Lifecycle;
+import com.android.settings.core.lifecycle.LifecycleObserver;
+import com.android.settings.core.lifecycle.events.OnResume;
+
+public abstract class DynamicAvailabilityPreferenceController extends PreferenceController
+        implements LifecycleObserver, OnResume {
+
+    private Preference mPreference;
+    private PreferenceScreen mScreen;
+
+    public DynamicAvailabilityPreferenceController(Context context, Lifecycle lifecycle) {
+        super(context);
+        if (lifecycle != null) {
+            lifecycle.addObserver(this);
+        }
+    }
+
+    @Override
+    public void displayPreference(PreferenceScreen screen) {
+        mScreen = screen;
+        mPreference = screen.findPreference(getPreferenceKey());
+        super.displayPreference(screen);
+    }
+
+    @Override
+    public void onResume() {
+        if (!isAvailable()) {
+            removePreference(mScreen, getPreferenceKey());
+            return;
+        }
+
+        updateState(mPreference);
+        if (mScreen.findPreference(getPreferenceKey()) == null) {
+            mScreen.addPreference(mPreference);
+        }
+    }
+}