Vertical scroll position should persist after setGroups call

[kodemi]

Hi! I receive data for Timeline dynamically and have to call setItems and setGroups every time I get new data. But setGroups resets vertical scroll position (I set the parameter height in options). You can see it here: https://codesandbox.io/s/vis-timeline-vertical-scroll-reset-bmoc1

[yotamberk]

Try doing this:

document.getElementById("update-button").onclick = () => {
  const scrollTop = document.getElementsByClassName("vis-vertical-scroll")[0].scrollTop;
  timeline.setGroups(groups);
  setTimeout(() => {
    document.getElementsByClassName("vis-vertical-scroll")[0].scrollTop = scrollTop ;
  }, 0);
};

If this isn't good enough for what you're looking for, feel free to reopen the issue

[kodemi]

Hi! I tried to set timeout and restore scrollTop, but it leads to flicker. I have updated codesandbox example to demonstrate it.

[kodemi]

Should be reopened but I have no rights to do it.

[kodemi]

Hi! I tried to set timeout and restore scrollTop, but it leads to flicker. I have updated codesandbox example to demonstrate it.

[kodemi]

I found that the problem appeared in v6.0.0. Comparing v6.0.0 with v5.1.0 and digging through code I found traces of problem:

1. setGroups call
2. Core.js _redraw() call and redraw of ItemSet
3. ItemSet redraws every group to calculate the sum of the height of the groups.
4. Group during redraw sets it's height to 0 and ItemSet sets it's height prop and frame height style to minHeight
5. _redraw() calls _updateScrollTop() and because this.props.center.height = 30 (minHeight) resets scrollTop to 0.

So group is failed to calculate its height in _calculateHeight because this.visibleItems = [] and this.props.label.height = 0. this.props.label.height will be updated to actual value only in next steps, after height calculation.

Quick fix is preset this.props.label in redraw() function in Group.js:

redraw(range, margin, forceRestack, returnQueue) {
    let resized = false;
    const lastIsVisible = this.isVisible;
    let height;
    const queue = [
      () => {
        forceRestack = this._didMarkerHeightChange.call(this) || forceRestack;
      },
      
      // recalculate the height of the subgroups
      this._updateSubGroupHeights.bind(this, margin),

      // calculate actual size and position
      this._calculateGroupSizeAndPosition.bind(this),

      () => {this._didResize.bind(this)(resized, this.height)}, // <----- adding this function call

      () => {
        this.isVisible = this._isGroupVisible.bind(this)(range, margin);
      },
...

And one of three:

1. comment these lines in _updateItemsInRange:

_updateItemsInRange(orderedItems, oldVisibleItems, range) {
   const visibleItems = [];
    const visibleItemsLookup = {}; // we keep this to quickly look up if an item already exists in the list without using indexOf on visibleItems

    //if (!this.isVisible && this.groupId != ReservedGroupIds.BACKGROUND) {
    //  for (let i = 0; i < oldVisibleItems.length; i++) {
    //    var item = oldVisibleItems[i];
    //    if (item.displayed) item.hide();
    //  }
    //  return visibleItems;
    //} 

    const interval = (range.end - range.start) / 4;
    ...

2. set group height in css:

.vis-panel.vis-left .vis-label .vis-inner {
  height: 40px;
}

3. set timeline option groupHeightMode: 'fixed'

Demos:

1. Combination of redraw() and _updateItemsInRange() changes: https://codesandbox.io/s/vis-timeline-jg9o6
2. Combination of redraw() and group height style: https://codesandbox.io/s/vis-timeline-hycf1
3. Combination of redraw() and option groupHeightMode: 'fixed': https://codesandbox.io/s/vis-timeline-ou1o0

[mckindd]

Is there any updates on a bug fix for this ticket?

I am running into the same issue in my current project. We had tried the original suggested fix to change the element a while back and that did not work or flickered depending on where it was used in React. The issue recently came back into discussion.

Any updates would be appreciated.

[TomHiller-swd]

@kodemi Thank you for this, I used the first option with patch-package to fix it.