Show custom notifications for API < 26.

app/src/main/java/org/thoughtcrime/securesms/groups/ui/managegroup/ManageGroupFragment.java

@@ -314,19 +314,17 @@ public class ManageGroupFragment extends Fragment {
       }
     });
 
-    if (NotificationChannels.supported()) {
     customNotificationsRow.setVisibility(View.VISIBLE);
 
     customNotificationsRow.setOnClickListener(v -> CustomNotificationsDialogFragment.create(groupId)
                                                                                     .show(requireFragmentManager(), "CUSTOM_NOTIFICATIONS"));
 
     //noinspection CodeBlock2Expr
+    if (NotificationChannels.supported()) {
       viewModel.hasCustomNotifications().observe(getViewLifecycleOwner(), hasCustomNotifications -> {
         customNotificationsButton.setText(hasCustomNotifications ? R.string.ManageGroupActivity_on
                                                                  : R.string.ManageGroupActivity_off);
       });
-    } else {
-      customNotificationsRow.setVisibility(View.GONE);
     }
 
     viewModel.getSnackbarEvents().observe(getViewLifecycleOwner(), this::handleSnackbarEvent);

app/src/main/java/org/thoughtcrime/securesms/groups/ui/managegroup/ManageGroupViewModel.java

@@ -31,6 +31,7 @@ import org.thoughtcrime.securesms.groups.ui.GroupChangeFailureReason;
 import org.thoughtcrime.securesms.groups.ui.GroupErrors;
 import org.thoughtcrime.securesms.groups.ui.GroupMemberEntry;
 import org.thoughtcrime.securesms.groups.ui.addmembers.AddMembersActivity;
+import org.thoughtcrime.securesms.notifications.NotificationChannels;
 import org.thoughtcrime.securesms.recipients.Recipient;
 import org.thoughtcrime.securesms.recipients.RecipientId;
 import org.thoughtcrime.securesms.recipients.RecipientUtil;
@@ -100,7 +101,7 @@ public class ManageGroupViewModel extends ViewModel {
     this.muteState                 = Transformations.map(this.groupRecipient,
                                                          recipient -> new MuteState(recipient.getMuteUntil(), recipient.isMuted()));
     this.hasCustomNotifications    = Transformations.map(this.groupRecipient,
-                                                         recipient -> recipient.getNotificationChannel() != null);
+                                                         recipient -> recipient.getNotificationChannel() != null || !NotificationChannels.supported());
     this.canLeaveGroup             = liveGroup.isActive();
     this.canBlockGroup             = Transformations.map(this.groupRecipient, recipient -> !recipient.isBlocked());
   }

app/src/main/java/org/thoughtcrime/securesms/groups/ui/notifications/CustomNotificationsDialogFragment.java

@@ -24,6 +24,7 @@ import androidx.lifecycle.ViewModelProviders;
 import org.thoughtcrime.securesms.R;
 import org.thoughtcrime.securesms.database.RecipientDatabase;
 import org.thoughtcrime.securesms.groups.GroupId;
+import org.thoughtcrime.securesms.notifications.NotificationChannels;
 import org.thoughtcrime.securesms.util.ThemeUtil;
 
 public class CustomNotificationsDialogFragment extends DialogFragment {
@@ -123,6 +124,11 @@ public class CustomNotificationsDialogFragment extends DialogFragment {
       vibrateSwitch.setVisibility(hasCustomNotifications ? View.VISIBLE : View.GONE);
     });
 
+    if (!NotificationChannels.supported()) {
+      customNotificationsSwitch.setVisibility(View.GONE);
+      view.findViewById(R.id.custom_notifications_enable_label).setVisibility(View.GONE);
+    }
+
     CompoundButton.OnCheckedChangeListener onVibrateSwitchCheckChangedListener = (buttonView, isChecked) -> {
       viewModel.setMessageVibrate(isChecked ? RecipientDatabase.VibrateState.ENABLED : RecipientDatabase.VibrateState.DISABLED);
     };

app/src/main/java/org/thoughtcrime/securesms/groups/ui/notifications/CustomNotificationsRepository.java

@@ -30,11 +30,13 @@ class CustomNotificationsRepository {
       Recipient         recipient         = getRecipient();
       RecipientDatabase recipientDatabase = DatabaseFactory.getRecipientDatabase(context);
 
+      if (NotificationChannels.supported()) {
         recipientDatabase.setMessageRingtone(recipient.getId(), NotificationChannels.getMessageRingtone(context, recipient));
         recipientDatabase.setMessageVibrate(recipient.getId(), NotificationChannels.getMessageVibrate(context, recipient) ? RecipientDatabase.VibrateState.ENABLED
                                                                                                                           : RecipientDatabase.VibrateState.DISABLED);
 
         NotificationChannels.ensureCustomChannelConsistency(context);
+      }
 
       onLoaded.run();
     });

app/src/main/java/org/thoughtcrime/securesms/groups/ui/notifications/CustomNotificationsViewModel.java

@@ -13,6 +13,7 @@ import androidx.lifecycle.ViewModelProvider;
 import org.thoughtcrime.securesms.database.RecipientDatabase;
 import org.thoughtcrime.securesms.groups.GroupId;
 import org.thoughtcrime.securesms.groups.LiveGroup;
+import org.thoughtcrime.securesms.notifications.NotificationChannels;
 import org.thoughtcrime.securesms.recipients.Recipient;
 
 public final class CustomNotificationsViewModel extends ViewModel {
@@ -27,7 +28,7 @@ public final class CustomNotificationsViewModel extends ViewModel {
   private CustomNotificationsViewModel(@NonNull GroupId groupId, @NonNull CustomNotificationsRepository repository) {
     this.liveGroup              = new LiveGroup(groupId);
     this.repository             = repository;
-    this.hasCustomNotifications = Transformations.map(liveGroup.getGroupRecipient(), recipient -> recipient.getNotificationChannel() != null);
+    this.hasCustomNotifications = Transformations.map(liveGroup.getGroupRecipient(), recipient -> recipient.getNotificationChannel() != null || !NotificationChannels.supported());
     this.isVibrateEnabled       = Transformations.map(liveGroup.getGroupRecipient(), Recipient::getMessageVibrate);
     this.notificationSound      = Transformations.map(liveGroup.getGroupRecipient(), Recipient::getMessageRingtone);
 

app/src/main/java/org/thoughtcrime/securesms/notifications/NotificationChannels.java

@@ -400,6 +400,9 @@ public class NotificationChannels {
   @TargetApi(26)
   @WorkerThread
   public static synchronized void ensureCustomChannelConsistency(@NonNull Context context) {
+    if (!supported()) {
+      return;
+    }
     Log.d(TAG, "ensureCustomChannelConsistency()");
 
     NotificationManager notificationManager = ServiceUtil.getNotificationManager(context);