Fix LHN flickers and scroll position restoring

[rezkiy37]

Explanation of Change

The PR enhances LHN (FlashList) performance. Especially when the user switches between tabs. It allows FlashList to avoid auto-measuring by setting the static estimated list size.

Fixed Issues

$ #53605
PROPOSAL: #53605 (comment)

Tests

• Verify that no errors appear in the JS console

1. Scroll LHN down.
2. Tap on the "Search" tab.
3. Tap on the "Inbox" tab.
4. Verify that LHN does not flicker when rendering rows.
5. Verify that LHN always scrolls on the correct previous position.

Offline tests

Same as "Tests".

QA Steps

// TODO: These must be filled out, or the issue title must include "[No QA]."

• Verify that no errors appear in the JS console

Same as "Tests".

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I added steps for the expected offline behavior in the Offline steps section
  • I added steps for Staging and/or Production testing in the QA steps section
  • I added steps to cover failure scenarios (i.e. verify an input displays the correct error message if the entered data is not correct)
  • I turned off my network connection and tested it while offline to ensure it matches the expected behavior (i.e. verify the default avatar icon is displayed if app is offline)
  • I tested this PR with a High Traffic account against the staging or production API to ensure there are no regressions (e.g. long loading states that impact usability).
• I included screenshots or videos for tests on all platforms
• I ran the tests on all platforms & verified they passed on:
  • Android: Native
  • Android: mWeb Chrome
  • iOS: Native
  • iOS: mWeb Safari
  • MacOS: Chrome / Safari
  • MacOS: Desktop
• I verified there are no console errors (if there's a console error not related to the PR, report it or open an issue for it to be fixed)
• I followed proper code patterns (see Reviewing the code)
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• If a new code pattern is added I verified it was agreed to be used by multiple Expensify engineers
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• I tested other components that can be impacted by my changes (i.e. if the PR modifies a shared library or component like Avatar, I verified the components using Avatar are working as expected)
• I verified all code is DRY (the PR doesn't include any logic written more than once, with the exception of tests)
• I verified any variables that can be defined as constants (ie. in CONST.ts or at the top of the file that uses the constant) are defined as such
• I verified that if a function's arguments changed that all usages have also been updated correctly
• If any new file was added I verified that:
  • The file has a description of what it does and/or why is needed at the top of the file if the code is not self explanatory
• If a new CSS style is added I verified that:
  • A similar style doesn't already exist
  • The style can't be created with an existing StyleUtils function (i.e. StyleUtils.getBackgroundAndBorderStyle(theme.componentBG))
• If the PR modifies code that runs when editing or sending messages, I tested and verified there is no unexpected behavior for all supported markdown - URLs, single line code, code blocks, quotes, headings, bold, strikethrough, and italic.
• If the PR modifies a generic component, I tested and verified that those changes do not break usages of that component in the rest of the App (i.e. if a shared library or component like Avatar is modified, I verified that Avatar is working as expected in all cases)
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  • I added Design label and/or tagged @Expensify/design so the design team can review the changes.
• If a new page is added, I verified it's using the ScrollView component to make it scrollable when more elements are added to the page.
• I added unit tests for any new feature or bug fix in this PR to help automatically prevent regressions in this user flow.
• If the main branch was merged into this PR after a review, I tested again and verified the outcome was still expected according to the Test steps.

Screenshots/Videos

Android: Native

Android.mp4

Android: mWeb Chrome

Android.Chrome.mp4

iOS: Native

IOS.mp4

iOS: mWeb Safari

IOS.Safari.mp4

MacOS: Chrome / Safari

Chrome.mp4

MacOS: Desktop

Desktop.mp4

[hungvu193]

@rezkiy37 It looks pretty cool so far. Can you resolve the linting and mark this as ready for review?

[rezkiy37]

@hungvu193, hi!
Yes, of course. Can we assume that the proposal has been approved?

[hungvu193]

@hungvu193, hi! Yes, of course. Can we assume that the proposal has been approved?

Yes. You got assigned to the issue already. Please go ahead 😄

[melvin-bot]

@hungvu193 Please copy/paste the Reviewer Checklist from here into a new comment on this PR and complete it. If you have the K2 extension, you can simply click: [this button]

[rezkiy37]

Local tests have passed well.

[hungvu193]

@rezkiy37 on mWeb Chrome, there's an empty view display for a while before LHN displays. It looks like it display the first index of LHN first then scroll to the current position.

Screen.Recording.2025-01-24.at.10.10.42.mov

[hungvu193]

It happens also on Desktop and Chrome

Screen.Recording.2025-01-24.at.10.29.45.mov

[rezkiy37]

@hungvu193, I am thinking about the next fix for web-based platforms. The app uses the scrollToOffset method anyway

App/src/components/LHNOptionsList/LHNOptionsList.tsx

Line 256 in 264728f

flashListRef.current.scrollToOffset({offset});

What if apply animated: true? It really smoothly scrolls to the previous position. When the list is extremely long it can take time to render items. However, it does not flicker. Yeah, there is a blank area but I don't think it is critical.

Moreover, the current behavior does not restore the position at all. So the user has to do it manually.

Video

Example.mp4

WDYT?

[hungvu193]

It looks weird to me 😄. I think that's fine to keep current behavior on web (stay at top) if we can't fix the empty issue.

Screen.Recording.2025-01-26.at.00.28.01.mov

[rezkiy37]

@hungvu193, well. I will apply the current changes for native platforms only for now. Also, I can work on a follow-up to find a web solution.

[hungvu193]

@hungvu193, well. I will apply the current changes for native platforms only for now. Also, I can work on a follow-up to find a web solution.

Thank you 😁

[rezkiy37]

@hungvu193, done 🙂

Video

Web.mp4

IOS.mp4

[hungvu193]

Ty. Look good to me. I'll complete the checklist today 🤞

[rezkiy37]

I've synced it up.

[puneetlath]

What list is this referring to? The LHN? Or any list?

Also, can we add some comments explaining what this is and when one might use it.

[rezkiy37]

The LHN. Working on it.

[rezkiy37]

Done - 717c184, 88f6bda.

[puneetlath]

Also, are there any tests we can add related to this change?

[rezkiy37]

Also, are there any tests we can add related to this change?

No, I don't think so.

[rezkiy37]

I've run the perf-test locally and it passed successfully.

[puneetlath]

I've run the Reassure test 3 times and it has failed every time. Can you look into it further @rezkiy37

[rezkiy37]

I've run the Reassure test 3 times and it has failed every time. Can you look into it further @rezkiy37

Yes, I can, However, I already have mentioned that it works properly for me locally. I will take a look one more time.

[rezkiy37]

@puneetlath, I just needed to mock the newly added hook in the test file. It works properly now. The tests have been passed. It is ready to merge 🙂

[github-actions]

🚀 Deployed to staging by https://github.com/puneetlath in version: 9.0.94-0 🚀

platform	result
🤖 android 🤖	success ✅
🖥 desktop 🖥	success ✅
🍎 iOS 🍎	success ✅
🕸 web 🕸	success ✅
🤖🔄 android HybridApp 🤖🔄	success ✅
🍎🔄 iOS HybridApp 🍎🔄	success ✅

[IuliiaHerets]

This PR is failing because of issue #56323

[rezkiy37]

@IuliiaHerets, this PR is not failing on the web because it fixes only native platforms.

[IuliiaHerets]

@rezkiy37 Ok, thanks for letting me know

[github-actions]

🚀 Deployed to production by https://github.com/AndrewGable in version: 9.0.94-25 🚀

platform	result
🤖 android 🤖	true ❌
🖥 desktop 🖥	cancelled 🔪
🍎 iOS 🍎	success ✅
🕸 web 🕸	success ✅
🤖🔄 android HybridApp 🤖🔄	failure ❌
🍎🔄 iOS HybridApp 🍎🔄	failure ❌

[github-actions]

🚀 Deployed to production by https://github.com/AndrewGable in version: 9.0.94-25 🚀

platform	result
🤖 android 🤖	true ❌
🖥 desktop 🖥	success ✅
🍎 iOS 🍎	success ✅
🕸 web 🕸	success ✅
🤖🔄 android HybridApp 🤖🔄	failure ❌
🍎🔄 iOS HybridApp 🍎🔄	failure ❌