Fix unresponsive UI during scan and display of "No Bluetooth devices"

- When there are no available Bluetooth devices, we show
  "No Bluetooth devices were found nearby" as a preference item after
  the scan completes. Update the layout for this Preference item so
  that the text is centered and doesn't highlight when touched.

- Fix slow responsiveness on scanning caused by repeated removal of
  "No Bluetooth devices were found" preference item on every call to
  onBindView().

- If no devices are paired, don't restart the scan on every rotation.

Bug: 5173935
Bug: 5055460
Change-Id: I52fb2d52f315c5e793f08499146842d54c5c3ead

res/layout/preference_empty_list.xml

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (C) 2011 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.
+-->
+
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:minHeight="48dip"
+    android:background="@android:color/transparent">
+
+    <TextView
+        android:id="@+android:id/title"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:padding="@*android:dimen/preference_fragment_padding_side"
+        android:gravity="center" />
+
+</LinearLayout>

src/com/android/settings/ProgressCategory.java

@@ -26,12 +26,13 @@ public class ProgressCategory extends ProgressCategoryBase {
 
     private boolean mProgress = false;
     private Preference mNoDeviceFoundPreference;
+    private boolean mNoDeviceFoundAdded;
 
     public ProgressCategory(Context context, AttributeSet attrs) {
         super(context, attrs);
         setLayoutResource(R.layout.preference_progress_category);
     }
-    
+
     @Override
     public void onBindView(View view) {
         super.onBindView(view);
@@ -39,21 +40,26 @@ public class ProgressCategory extends ProgressCategoryBase {
         final View progressBar = view.findViewById(R.id.scanning_progress);
 
         textView.setText(mProgress ? R.string.progress_scanning : R.string.progress_tap_to_pair);
-        boolean noDeviceFound = getPreferenceCount() == 0;
+        boolean noDeviceFound = (getPreferenceCount() == 0 ||
+                (getPreferenceCount() == 1 && getPreference(0) == mNoDeviceFoundPreference));
         textView.setVisibility(noDeviceFound ? View.INVISIBLE : View.VISIBLE);
         progressBar.setVisibility(mProgress ? View.VISIBLE : View.INVISIBLE);
 
         if (mProgress) {
-            if (mNoDeviceFoundPreference != null) {
+            if (mNoDeviceFoundAdded) {
                 removePreference(mNoDeviceFoundPreference);
+                mNoDeviceFoundAdded = false;
             }
         } else {
-            if (noDeviceFound) {
+            if (noDeviceFound && !mNoDeviceFoundAdded) {
                 if (mNoDeviceFoundPreference == null) {
                     mNoDeviceFoundPreference = new Preference(getContext());
-                    mNoDeviceFoundPreference.setSummary(R.string.bluetooth_no_devices_found);
+                    mNoDeviceFoundPreference.setLayoutResource(R.layout.preference_empty_list);
+                    mNoDeviceFoundPreference.setTitle(R.string.bluetooth_no_devices_found);
+                    mNoDeviceFoundPreference.setSelectable(false);
                 }
                 addPreference(mNoDeviceFoundPreference);
+                mNoDeviceFoundAdded = true;
             }
         }
     }

src/com/android/settings/bluetooth/BluetoothSettings.java

@@ -99,8 +99,8 @@ public final class BluetoothSettings extends DeviceListPreferenceFragment {
 
     @Override
     public void onActivityCreated(Bundle savedInstanceState) {
-        mActivityStarted = true;
         super.onActivityCreated(savedInstanceState);
+        mActivityStarted = (savedInstanceState == null);    // don't auto start scan after rotation
 
         mEmptyView = (TextView) getView().findViewById(android.R.id.empty);
         getListView().setEmptyView(mEmptyView);