Fix some issues with notif blocking in settings

- Fix cast cast exception
- Make sure unblocking a notification channel also actually
unblocks it

Test: make -j64 RunSettingsRoboTests ROBOTEST_FILTER="com.android.settings.notification"
Fixes: 177968301
Fixes: 177907827
Change-Id: Ibad56e102e167bcf004fbd0f9873cc29834a30c1

res/xml/channel_notification_settings.xml

@@ -25,10 +25,9 @@
         android:order="1"
         android:layout="@layout/settings_entity_header" />
 
-    <com.android.settingslib.widget.LayoutPreference
+    <com.android.settings.widget.SettingsMainSwitchPreference
         android:key="block"
-        android:order="2"
-        android:layout="@layout/styled_switch_bar" />
+        android:order="2" />
 
     <!-- Importance toggle -->
     <com.android.settingslib.RestrictedSwitchPreference

src/com/android/settings/notification/app/BlockPreferenceController.java

@@ -16,6 +16,7 @@
 
 package com.android.settings.notification.app;
 
+import static android.app.NotificationManager.IMPORTANCE_LOW;
 import static android.app.NotificationManager.IMPORTANCE_NONE;
 import static android.app.NotificationManager.IMPORTANCE_UNSPECIFIED;
 
@@ -107,7 +108,7 @@ public class BlockPreferenceController extends NotificationPreferenceController
                         ? IMPORTANCE_NONE
                         : isDefaultChannel()
                                 ? IMPORTANCE_UNSPECIFIED
-                                : mChannel.getOriginalImportance();
+                                : Math.max(mChannel.getOriginalImportance(), IMPORTANCE_LOW);
                 mChannel.setImportance(importance);
                 saveChannel();
             }

src/com/android/settings/notification/app/ChannelListPreferenceController.java

@@ -339,7 +339,9 @@ public class ChannelListPreferenceController extends NotificationPreferenceContr
         channelPref.setOnPreferenceChangeListener(
                 (preference, o) -> {
                     boolean value = (Boolean) o;
-                    int importance = value ? channel.getOriginalImportance() : IMPORTANCE_NONE;
+                    int importance = value
+                            ? Math.max(channel.getOriginalImportance(), IMPORTANCE_LOW)
+                            : IMPORTANCE_NONE;
                     channel.setImportance(importance);
                     channel.lockFields(NotificationChannel.USER_LOCKED_IMPORTANCE);
                     PrimarySwitchPreference channelPref1 = (PrimarySwitchPreference) preference;