Fix NPE with registering content listener

1) Fix the condition to check either subscribed or null.
2) Don't register listeners unless the feature flag is enabled

Test: make RunSettingsRoboTest
Bug: 267357231
Change-Id: I0134812cbac60c394d96c5a5621a7c16d781b05d

src/com/android/settings/biometrics/activeunlock/ActiveUnlockContentListener.java

@@ -87,10 +87,10 @@ public class ActiveUnlockContentListener {
 
     }
 
-    /** Starts listening for updates from the ContentProvider, and fetches the current value. */
-    public synchronized void subscribe() {
-        if (mSubscribed && mUri != null) {
-            return;
+    /** Returns true if start listening for updates from the ContentProvider, false otherwise. */
+    public synchronized boolean subscribe() {
+        if (mSubscribed || mUri == null) {
+            return false;
         }
         mSubscribed = true;
         mContext.getContentResolver().registerContentObserver(
@@ -99,15 +99,17 @@ public class ActiveUnlockContentListener {
                 () -> {
                     getContentFromUri();
                 });
+        return true;
     }
 
-    /** Stops listening for updates from the ContentProvider. */
-    public synchronized void unsubscribe() {
-        if (!mSubscribed && mUri != null) {
-            return;
+    /** Returns true if stops listening for updates from the ContentProvider, false otherewise. */
+    public synchronized boolean unsubscribe() {
+        if (!mSubscribed || mUri == null) {
+            return false;
         }
         mSubscribed = false;
         mContext.getContentResolver().unregisterContentObserver(mContentObserver);
+        return true;
     }
 
     /** Retrieves the most recently fetched value from the ContentProvider. */

src/com/android/settings/biometrics/activeunlock/ActiveUnlockStatusPreferenceController.java

@@ -50,6 +50,7 @@ public class ActiveUnlockStatusPreferenceController
     private final CombinedBiometricStatusUtils mCombinedBiometricStatusUtils;
     private final ActiveUnlockSummaryListener mActiveUnlockSummaryListener;
     private final ActiveUnlockDeviceNameListener mActiveUnlockDeviceNameListener;
+    private final boolean mIsAvailable;
 
     public ActiveUnlockStatusPreferenceController(@NonNull Context context) {
         this(context, KEY_ACTIVE_UNLOCK_SETTINGS);
@@ -59,6 +60,7 @@ public class ActiveUnlockStatusPreferenceController
             @NonNull Context context, @NonNull String key) {
         super(context, key);
         mActiveUnlockStatusUtils = new ActiveUnlockStatusUtils(context);
+        mIsAvailable = mActiveUnlockStatusUtils.isAvailable();
         mCombinedBiometricStatusUtils = new CombinedBiometricStatusUtils(context, getUserId());
         OnContentChangedListener onSummaryChangedListener = new OnContentChangedListener() {
             @Override
@@ -90,8 +92,10 @@ public class ActiveUnlockStatusPreferenceController
     /** Subscribes to update preference summary dynamically. */
     @OnLifecycleEvent(Lifecycle.Event.ON_START)
     public void onStart() {
-        mActiveUnlockSummaryListener.subscribe();
-        mActiveUnlockDeviceNameListener.subscribe();
+        if (mIsAvailable) {
+            mActiveUnlockSummaryListener.subscribe();
+            mActiveUnlockDeviceNameListener.subscribe();
+        }
     }
 
     /** Resets the preference reference on resume. */
@@ -105,8 +109,10 @@ public class ActiveUnlockStatusPreferenceController
     /** Unsubscribes to prevent leaked listener. */
     @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
     public void onStop() {
-        mActiveUnlockSummaryListener.unsubscribe();
-        mActiveUnlockDeviceNameListener.unsubscribe();
+        if (mIsAvailable) {
+            mActiveUnlockSummaryListener.unsubscribe();
+            mActiveUnlockDeviceNameListener.unsubscribe();
+        }
     }
 
     @Override
@@ -127,7 +133,7 @@ public class ActiveUnlockStatusPreferenceController
         // This should never be called, as getAvailabilityStatus() will return the exact value.
         // However, this is an abstract method in BiometricStatusPreferenceController, and so
         // needs to be overridden.
-        return mActiveUnlockStatusUtils.isAvailable();
+        return mIsAvailable;
     }
 
     @Override