Remove NFC Slice jank

The NFC Slice would jank on enable and disable, because of the
intent filter it registered with SysUI. The intent filter would
broadcast an update for four states:
1) On
2) Off
3) Turning On
4) Turning off

The first two caused no problems. The third and fourth caused jank,
since when clicked, the switch in the NFC slice would turn on / off
asynchronously - that is, it turned on or off based on the previous
state of the switch, rather than on the actual value of NFC. It does
this to feel fluid in the app in which it is rendered.

From the off state, the order of events is:
1.  Switch clicked
2.  Switch animates on
2.  Background intent is fired to settings to turn on Nfc (happens at
       the same time as animation)
3.  Settings calls the NFC enable API
4.  A broadcast for Turning On is sent
5.  The receiver in SysUI gets the broadcast and forwards it to settings
6.  Settings tells the Slice to make sure it is up to date
7.  The Slice checks for the current value - IMPORTANTLY - which is
        currently off, it is only in the process of being enabled.
8.  The Slice flips back off
9.  Nfc finishes getting enabled in the background
10. The framework pushes the NFC ON broadcast
11. SysUI gets the broadcast, and forwards it to settings
12. Settings tells the slice to update
13. The slice checks again and finds that NFC is on, flipping on.

This CL creates a new background slice worker for NFC and registers
the intent filter there, rather than in SysUI. When the background
worker gets the broadcast, it checks if it is in state 3/4, and if so,
it drops the update silently.

Fixes: 115737701
Test: robotests
Change-Id: I17043828ad3a67a2a5acdf5c75d9cc51ff7e91d0

src/com/android/settings/nfc/NfcPreferenceController.java

@@ -15,20 +15,26 @@
  */
 package com.android.settings.nfc;
 
+import android.content.BroadcastReceiver;
 import android.content.Context;
+import android.content.Intent;
 import android.content.IntentFilter;
+import android.net.Uri;
 import android.nfc.NfcAdapter;
 import android.provider.Settings;
-
+import android.util.Log;
 import androidx.annotation.VisibleForTesting;
 import androidx.preference.PreferenceScreen;
 import androidx.preference.SwitchPreference;
 
 import com.android.settings.core.TogglePreferenceController;
+import com.android.settings.slices.SliceBackgroundWorker;
 import com.android.settingslib.core.lifecycle.LifecycleObserver;
 import com.android.settingslib.core.lifecycle.events.OnPause;
 import com.android.settingslib.core.lifecycle.events.OnResume;
 
+import java.io.IOException;
+
 public class NfcPreferenceController extends TogglePreferenceController
         implements LifecycleObserver, OnResume, OnPause {
 
@@ -51,8 +57,7 @@ public class NfcPreferenceController extends TogglePreferenceController
             return;
         }
 
-        final SwitchPreference switchPreference =
-                (SwitchPreference) screen.findPreference(getPreferenceKey());
+        final SwitchPreference switchPreference = screen.findPreference(getPreferenceKey());
 
         mNfcEnabler = new NfcEnabler(mContext, switchPreference);
 
@@ -86,14 +91,6 @@ public class NfcPreferenceController extends TogglePreferenceController
                 : UNSUPPORTED_ON_DEVICE;
     }
 
-    @Override
-    public IntentFilter getIntentFilter() {
-        final IntentFilter filter = new IntentFilter();
-        filter.addAction(NfcAdapter.ACTION_ADAPTER_STATE_CHANGED);
-        filter.addAction(NfcAdapter.EXTRA_ADAPTER_STATE);
-        return filter;
-    }
-
     @Override
     public boolean hasAsyncUpdate() {
         return true;
@@ -104,6 +101,11 @@ public class NfcPreferenceController extends TogglePreferenceController
         return true;
     }
 
+    @Override
+    public Class<? extends SliceBackgroundWorker> getBackgroundWorkerClass() {
+        return NfcSliceWorker.class;
+    }
+
     @Override
     public void onResume() {
         if (mAirplaneModeObserver != null) {
@@ -135,4 +137,77 @@ public class NfcPreferenceController extends TogglePreferenceController
                 Settings.Global.AIRPLANE_MODE_TOGGLEABLE_RADIOS);
         return toggleable != null && toggleable.contains(Settings.Global.RADIO_NFC);
     }
+
+    /**
+     * Listener for background changes to NFC.
+     *
+     * <p>
+     *     Listen to broadcasts from {@link NfcAdapter}. The worker will call notify changed on the
+     *     NFC Slice only when the following extras are present in the broadcast:
+     *     <ul>
+     *      <li>{@link NfcAdapter#STATE_ON}</li>
+     *      <li>{@link NfcAdapter#STATE_OFF}</li>
+     *     </ul>
+     */
+    public static class NfcSliceWorker extends SliceBackgroundWorker<Void> {
+
+        private static final String TAG = "NfcSliceWorker";
+
+        private static final IntentFilter NFC_FILTER =
+                new IntentFilter(NfcAdapter.ACTION_ADAPTER_STATE_CHANGED);
+
+        private NfcUpdateReceiver mUpdateObserver;
+
+        public NfcSliceWorker(Context context, Uri uri) {
+            super(context, uri);
+            mUpdateObserver = new NfcUpdateReceiver(this);
+        }
+
+        @Override
+        protected void onSlicePinned() {
+            getContext().registerReceiver(mUpdateObserver, NFC_FILTER);
+        }
+
+        @Override
+        protected void onSliceUnpinned() {
+            getContext().unregisterReceiver(mUpdateObserver);
+        }
+
+        @Override
+        public void close() throws IOException {
+            mUpdateObserver = null;
+        }
+
+        public void updateSlice() {
+            notifySliceChange();
+        }
+
+        public class NfcUpdateReceiver extends BroadcastReceiver {
+
+            private final int NO_EXTRA = -1;
+
+            private final NfcSliceWorker mSliceBackgroundWorker;
+
+            public NfcUpdateReceiver(NfcSliceWorker sliceWorker) {
+                mSliceBackgroundWorker = sliceWorker;
+            }
+
+            @Override
+            public void onReceive(Context context, Intent intent) {
+                final int nfcStateExtra = intent.getIntExtra(NfcAdapter.EXTRA_ADAPTER_STATE,
+                        NO_EXTRA);
+
+                // Do nothing if state change is empty, or an intermediate step.
+                if ( (nfcStateExtra == NO_EXTRA)
+                        || (nfcStateExtra == NfcAdapter.STATE_TURNING_ON)
+                        || (nfcStateExtra == NfcAdapter.STATE_TURNING_OFF)) {
+                    Log.d(TAG, "Transitional update, dropping broadcast");
+                    return;
+                }
+
+                Log.d(TAG, "Nfc broadcast received, updating Slice.");
+                mSliceBackgroundWorker.updateSlice();
+            }
+        }
+    }
 }