Optimize RecyclerView performance after returning from NoteEditActivity (scroll position, lag, unnecessary re-rendering)

[amarradi]

📝 Description

When returning from NoteEditActivity to MainActivity, the app currently reloads the entire note list, resulting in a noticeable jump (especially in GridView layout) and UI lag before the list becomes usable. This negatively impacts user experience, particularly with many notes or when the ReleaseNote header is visible.

🔍 Observed behavior

• After closing NoteEditActivity, noteViewModel.loadNotes() is called in MainActivity.
• This triggers the observer for notesLiveData, which in turn calls noteAdapter.updateNotes(...).
• That invokes DiffUtil.calculateDiff(...) internally, causing the entire adapter content to be recalculated.
• Then, recyclerView.scrollToPosition(...) is called to restore the previous scroll position.
• This entire sequence happens on the UI thread, leading to stuttering and visible jumping.
• With StaggeredGridLayoutManager, layouting is especially expensive.

⚠️ Root cause

• loadNotes() always loads the full note list, even when only one note was edited or created.
• This causes a full rebind in the adapter, triggering layout invalidation.
• Scroll restoration occurs too early, before RecyclerView has finished layouting.
• The ReleaseNote header is reset on every return, even if unchanged → triggers layout recalculation.

✅ Expected behavior

• Only update the changed or new note in the list (e.g., via updateSingleNote(...)).
• Avoid full list reload unless necessary.
• Restore scroll position only after RecyclerView layout is complete, ideally without expensive ViewTreeObserver.
• Only update the ReleaseNote header if its content actually changed.

✅ Suggested solution (for next version)

1. Add updateSingleNote(Note note) method in NoteViewModel

• Replaces the matching note in the notesLiveData list.
• Triggers a minimal update via setValue().

2. In NoteEditActivity

• Add the updated note to the result Intent:

  intent.putExtra("updated_note", note);
  setResult(RESULT_OK, intent);

3. In MainActivity

• Handle the updated note in ActivityResultLauncher:

  if (result.getResultCode() == RESULT_OK) {
      Intent data = result.getData();
      if (data != null && data.hasExtra("updated_note")) {
          Note updated = data.getParcelableExtra("updated_note");
          noteViewModel.updateSingleNote(updated);
          scrollAfterLoadToPosition = lastScrollPosition;
      }
  }

• Do not call loadNotes() after every return unless absolutely necessary (e.g., delete or category switch).

4. Restore scroll position using recyclerView.post(...), only if scrollAfterLoadToPosition >= 0.

5. Prevent unnecessary ReleaseNote updates

if (!releaseNote.equals(noteAdapter.getReleaseNote())) {
    noteAdapter.setReleaseNoteHeader(releaseNote);
}

🛠 To-do list

• Add updateSingleNote(...) method to NoteViewModel
• Return updated_note from NoteEditActivity using Intent.putExtra
• In MainActivity, avoid loadNotes() after return and use the new update method instead
• Move scroll restoration logic into the notesLiveData observer
• Add check to avoid resetting the ReleaseNote header if it's unchanged
• Optionally, also improve onReleaseNoteClosed() to avoid unnecessary reloads

🕓 Timing

This optimization is scheduled for a future release to allow a clean and well-tested implementation.

🧩 Affected components

• MainActivity.java
• NoteViewModel.java
• NoteEditActivity.java
• NoteAdapter.java