Grey the previously connected device preference

* For fix the TreeHugger error in pi-dev, cherry pick the ag/3935357 in
  master and fix TreeHugger error.
* Add PreviouslyConnectedDevicePreferenceController to handle the preference should be
  enable or disable.
  Example: If there are no previously connected devices disable the preference otherwise
  enable it.
* Add PreviouslyConnectedDevicePreferenceControllerTest
  1. Verify the callback can be registered and unregistered
  2. Verify the preference is enable when there
     have more than 1 previously connected device
  3. Verify the preference is disable when there
     have no previously connected device

Bug: 78250052
Test: make -j50 RunSettingsRoboTests
Change-Id: I31b5d416aaf907c3bbf1cb61de6e7401463e3df7

src/com/android/settings/connecteddevice/PreviouslyConnectedDevicePreferenceController.java

@@ -0,0 +1,108 @@
+/*
+ * Copyright 2018 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.connecteddevice;
+
+import android.content.Context;
+import android.content.pm.PackageManager;
+
+import androidx.annotation.VisibleForTesting;
+import androidx.preference.Preference;
+import androidx.preference.PreferenceScreen;
+import com.android.settings.bluetooth.BluetoothDeviceUpdater;
+import com.android.settings.bluetooth.SavedBluetoothDeviceUpdater;
+import com.android.settings.core.BasePreferenceController;
+import com.android.settings.dashboard.DashboardFragment;
+
+import com.android.settingslib.core.lifecycle.LifecycleObserver;
+import com.android.settingslib.core.lifecycle.events.OnStart;
+import com.android.settingslib.core.lifecycle.events.OnStop;
+
+public class PreviouslyConnectedDevicePreferenceController extends BasePreferenceController
+        implements LifecycleObserver, OnStart, OnStop, DevicePreferenceCallback {
+
+    private Preference mPreference;
+    private BluetoothDeviceUpdater mBluetoothDeviceUpdater;
+    private int mPreferenceSize;
+
+    public PreviouslyConnectedDevicePreferenceController(Context context, String preferenceKey) {
+        super(context, preferenceKey);
+    }
+
+    @Override
+    public int getAvailabilityStatus() {
+        return mContext.getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH)
+                ? AVAILABLE
+                : CONDITIONALLY_UNAVAILABLE;
+    }
+
+    @Override
+    public void displayPreference(PreferenceScreen screen) {
+        super.displayPreference(screen);
+        if (isAvailable()) {
+            mPreference = screen.findPreference(getPreferenceKey());
+            mBluetoothDeviceUpdater.setPrefContext(screen.getContext());
+        }
+    }
+
+    @Override
+    public void onStart() {
+        mBluetoothDeviceUpdater.registerCallback();
+        updatePreferenceOnSizeChanged();
+    }
+
+    @Override
+    public void onStop() {
+        mBluetoothDeviceUpdater.unregisterCallback();
+    }
+
+    public void init(DashboardFragment fragment) {
+        mBluetoothDeviceUpdater = new SavedBluetoothDeviceUpdater(fragment.getContext(),
+                fragment, PreviouslyConnectedDevicePreferenceController.this);
+    }
+
+    @Override
+    public void onDeviceAdded(Preference preference) {
+        mPreferenceSize++;
+        updatePreferenceOnSizeChanged();
+    }
+
+    @Override
+    public void onDeviceRemoved(Preference preference) {
+        mPreferenceSize--;
+        updatePreferenceOnSizeChanged();
+    }
+
+    @VisibleForTesting
+    void setBluetoothDeviceUpdater(BluetoothDeviceUpdater bluetoothDeviceUpdater) {
+        mBluetoothDeviceUpdater = bluetoothDeviceUpdater;
+    }
+
+    @VisibleForTesting
+    void setPreferenceSize(int size) {
+        mPreferenceSize = size;
+    }
+
+    @VisibleForTesting
+    void setPreference(Preference preference) {
+        mPreference = preference;
+    }
+
+    private void updatePreferenceOnSizeChanged() {
+        if (isAvailable()) {
+            mPreference.setEnabled(mPreferenceSize != 0);
+        }
+    }
+}