Retain scroll position in paged lists

app/src/main/java/com/todoroo/astrid/activity/TaskListFragment.java

@@ -275,7 +275,12 @@ public final class TaskListFragment extends InjectingFragment
                 taskListViewModel.getValue(),
                 taskDao)
             : new PagedListRecyclerAdapter(
-                taskAdapter, viewHolderFactory, this, taskListViewModel.getValue(), taskDao);
+                taskAdapter,
+                recyclerView,
+                viewHolderFactory,
+                this,
+                taskListViewModel.getValue(),
+                taskDao);
     taskAdapter.setHelper(recyclerAdapter);
     ((DefaultItemAnimator) recyclerView.getItemAnimator()).setSupportsChangeAnimations(false);
     recyclerView.setLayoutManager(new LinearLayoutManager(context));

app/src/main/java/org/tasks/tasklist/PagedListRecyclerAdapter.java

@@ -1,8 +1,10 @@
 package org.tasks.tasklist;
 
+import android.os.Parcelable;
 import androidx.paging.AsyncPagedListDiffer;
 import androidx.paging.PagedList;
 import androidx.recyclerview.widget.AsyncDifferConfig;
+import androidx.recyclerview.widget.RecyclerView;
 import com.todoroo.astrid.activity.TaskListFragment;
 import com.todoroo.astrid.adapter.TaskAdapter;
 import com.todoroo.astrid.dao.TaskDao;
@@ -11,15 +13,18 @@ import org.tasks.data.TaskContainer;
 
 public class PagedListRecyclerAdapter extends TaskListRecyclerAdapter {
 
+  private final RecyclerView recyclerView;
   private AsyncPagedListDiffer<TaskContainer> differ;
 
   public PagedListRecyclerAdapter(
       TaskAdapter adapter,
+      RecyclerView recyclerView,
       ViewHolderFactory viewHolderFactory,
       TaskListFragment taskList,
       List<TaskContainer> list,
       TaskDao taskDao) {
     super(adapter, viewHolderFactory, taskList, taskDao);
+    this.recyclerView = recyclerView;
     differ =
         new AsyncPagedListDiffer<>(
             this, new AsyncDifferConfig.Builder<>(new ItemCallback()).build());
@@ -37,6 +42,15 @@ public class PagedListRecyclerAdapter extends TaskListRecyclerAdapter {
     differ.submitList((PagedList<TaskContainer>) list);
   }
 
+  @Override
+  public void onMoved(int fromPosition, int toPosition) {
+    Parcelable recyclerViewState = recyclerView.getLayoutManager().onSaveInstanceState();
+
+    super.onMoved(fromPosition, toPosition);
+
+    recyclerView.getLayoutManager().onRestoreInstanceState(recyclerViewState);
+  }
+
   @Override
   public int getItemCount() {
     return differ.getItemCount();