[BUG] [Mobile] [Web] Jump to the bottom of next page when scrolling forward

[Te-Z]

Reproduce steps:

• In a room, jump to a pinned message or to the last unread message
• Scroll forward
• load next page

Actual:

Jump to the bottom of next page, so the user has to scroll backward to continue where he left

Expected:

Next page loads without moving the scroll position

Capture.video.du.27-03-2024.06.41.10.webm

screen-20240327-070619.mp4

[Te-Z]

The problem is we need to know the position (in px) of the item at index 0 before scrolling forward. This way when new items will be inserted starting from this index, the UI won't move.

I tried with infinite_pagination_list (#1681) but couldn't achieve to load correctly the data. But I have a functional POC: https://github.com/Te-Z/flutter_biderectional_pagination .

Solution found here: EdsonBueno/infinite_scroll_pagination#56 (comment)

[Te-Z]

I also tried with a custom scroll physic, but I'm struggling a bit to find the good way to calculate the good position to keep since every item can have a different size.

See this branch: https://github.com/linagora/twake-on-matrix/tree/TW-1634/custom_scroll_physics

import 'package:flutter/material.dart';

class PositionRetainedScrollPhysics extends ScrollPhysics {
  final bool shouldRetain;
  const PositionRetainedScrollPhysics(
      {ScrollPhysics? parent, this.shouldRetain = true})
      : super(parent: parent);

  @override
  PositionRetainedScrollPhysics applyTo(ScrollPhysics? ancestor) {
    return PositionRetainedScrollPhysics(
      parent: buildParent(ancestor),
      shouldRetain: shouldRetain,
    );
  }

  @override
  double adjustPositionForNewDimensions({
    required ScrollMetrics oldPosition,
    required ScrollMetrics newPosition,
    required bool isScrolling,
    required double velocity,
  }) {
    final position = super.adjustPositionForNewDimensions(
      oldPosition: oldPosition,
      newPosition: newPosition,
      isScrolling: isScrolling,
      velocity: velocity,
    );

    final diff = newPosition.maxScrollExtent - oldPosition.maxScrollExtent;
    if (oldPosition.pixels == 0 && newPosition.pixels == 0) {
      if (newPosition.maxScrollExtent > oldPosition.maxScrollExtent &&
          diff > 0 &&
          shouldRetain) {
        return diff;
      } else {
        return position;
      }
    } else {
      return position;
    }
  }
}

[Te-Z]

removing this ticket from In Progresscolumn for now since no solutions worked at the moment