Update selection in FileListListAdapter using ID received from list instead of position, so that changes removals or additions in the list result in correct update of the drawn selection

src/com/owncloud/android/ui/adapter/FileListListAdapter.java

@@ -476,17 +476,12 @@ public class FileListListAdapter extends BaseAdapter implements ListAdapter {
         return mSelection.contains(getItemId(position));
     }
 
-    public void updateSelection(int position, boolean checked) {
+    public void updateSelection(long itemId, boolean checked) {
         if (checked) {
-            mSelection.add(getItemId(position));
-            notifyDataSetChanged();
+            mSelection.add(itemId);
         } else {
-            removeSelection(position);
+            mSelection.remove(itemId);
         }
-    }
-
-    public void removeSelection(int position) {
-        mSelection.remove(getItemId(position));
         notifyDataSetChanged();
     }
 

src/com/owncloud/android/ui/fragment/OCFileListFragment.java

@@ -349,7 +349,7 @@ public class OCFileListFragment extends ExtendedListFragment {
 
             @Override
             public void onItemCheckedStateChanged(ActionMode mode, int position, long id, boolean checked) {
-                mAdapter.updateSelection(position, checked);
+                mAdapter.updateSelection(id, checked);
                 mode.invalidate();
             }
 
@@ -376,18 +376,17 @@ public class OCFileListFragment extends ExtendedListFragment {
 
             @Override
             public boolean onPrepareActionMode(ActionMode mode, Menu menu) {
-                final int checkedCount = getListView().getCheckedItemCount();
+                List<OCFile> checkedFiles = mAdapter.getCheckedItems();
+                final int checkedCount = checkedFiles.size();
                 String title = getResources().getQuantityString(
                     R.plurals.items_selected_count,
                     checkedCount,
                     checkedCount
                 );
                 mode.setTitle(title);
-
                 if (checkedCount > 0) {
-                    List<OCFile> targetFiles = mAdapter.getCheckedItems();
                     FileMenuFilter mf = new FileMenuFilter(
-                        targetFiles,
+                        checkedFiles,
                         ((FileActivity) getActivity()).getAccount(),
                         mContainerActivity,
                         getActivity()