Low priority paging

app/src/main/java/eu/faircode/email/FragmentMessages.java

@@ -50,6 +50,8 @@ import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
@@ -125,6 +127,8 @@ public class FragmentMessages extends FragmentEx {
 
     private BoundaryCallbackMessages searchCallback = null;
 
+    private ExecutorService executor = Executors.newSingleThreadExecutor(Helper.backgroundThreadFactory);
+
     private static final int LOCAL_PAGE_SIZE = 100;
     private static final int REMOTE_PAGE_SIZE = 10;
     private static final int UNDO_TIMEOUT = 5000; // milliseconds
@@ -1622,7 +1626,6 @@ public class FragmentMessages extends FragmentEx {
         model.set(getContext(), folder, search, REMOTE_PAGE_SIZE);
 
         // Observe folder/messages/search
-        if (TextUtils.isEmpty(search)) {
         SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getContext());
         String sort = prefs.getString("sort", "time");
         boolean debug = prefs.getBoolean("debug", false);
@@ -1631,10 +1634,11 @@ public class FragmentMessages extends FragmentEx {
         if (messages != null)
             messages.removeObservers(getViewLifecycleOwner());
 
+        LivePagedListBuilder<Integer, TupleMessageEx> builder = null;
         switch (viewType) {
             case UNIFIED:
-                    messages = new LivePagedListBuilder<>(
-                            db.message().pagedUnifiedInbox(threading, sort, debug), LOCAL_PAGE_SIZE).build();
+                builder = new LivePagedListBuilder<>(
+                        db.message().pagedUnifiedInbox(threading, sort, debug), LOCAL_PAGE_SIZE);
                 break;
 
             case FOLDER:
@@ -1662,23 +1666,21 @@ public class FragmentMessages extends FragmentEx {
                                 }
                             });
 
-                    PagedList.Config config = new PagedList.Config.Builder()
+                PagedList.Config configFolder = new PagedList.Config.Builder()
                         .setPageSize(LOCAL_PAGE_SIZE)
                         .setPrefetchDistance(REMOTE_PAGE_SIZE)
                         .build();
-                    LivePagedListBuilder<Integer, TupleMessageEx> builder = new LivePagedListBuilder<>(
-                            db.message().pagedFolder(folder, threading, sort, false, debug), config);
+                builder = new LivePagedListBuilder<>(
+                        db.message().pagedFolder(folder, threading, sort, false, debug), configFolder);
                 builder.setBoundaryCallback(searchCallback);
-                    messages = builder.build();
-
                 break;
 
             case THREAD:
-                    messages = new LivePagedListBuilder<>(
-                            db.message().pagedThread(account, thread, threading ? null : id, debug), LOCAL_PAGE_SIZE).build();
+                builder = new LivePagedListBuilder<>(
+                        db.message().pagedThread(account, thread, threading ? null : id, debug), LOCAL_PAGE_SIZE);
                 break;
-            }
-        } else {
+
+            case SEARCH:
                 if (searchCallback == null)
                     searchCallback = new BoundaryCallbackMessages(this, model,
                             new BoundaryCallbackMessages.IBoundaryCallbackMessages() {
@@ -1706,16 +1708,19 @@ public class FragmentMessages extends FragmentEx {
                                 }
                             });
 
-            PagedList.Config config = new PagedList.Config.Builder()
+                PagedList.Config configSearch = new PagedList.Config.Builder()
                         .setPageSize(LOCAL_PAGE_SIZE)
                         .setPrefetchDistance(REMOTE_PAGE_SIZE)
                         .build();
-            LivePagedListBuilder<Integer, TupleMessageEx> builder = new LivePagedListBuilder<>(
-                    db.message().pagedFolder(folder, threading, "time", true, false), config);
+                builder = new LivePagedListBuilder<>(
+                        db.message().pagedFolder(folder, threading, "time", true, false), configSearch);
                 builder.setBoundaryCallback(searchCallback);
-            messages = builder.build();
+                break;
         }
 
+        builder.setFetchExecutor(executor);
+
+        messages = builder.build();
         messages.observe(getViewLifecycleOwner(), new Observer<PagedList<TupleMessageEx>>() {
             @Override
             public void onChanged(@Nullable PagedList<TupleMessageEx> messages) {