scrollTop not working if rendered with 0 items

Hey,

Thanks for the great lib.

I am trying to set the scrollTop prop on a List that is wrapped by an InfiniteScroller. During the first render the list’s rowCount is 0, and after that all scrollTop is ignored, and always stays at 0.

In https://github.com/bvaughn/react-virtualized/blob/master/source/Grid/Grid.js, line 596:

componentWillReceiveProps (nextProps) {
    const { scrollLeft, scrollTop } = this.state

    if (
      nextProps.columnCount === 0 &&
      scrollLeft !== 0 ||
      nextProps.rowCount === 0 &&
      scrollTop !== 0
    ) {
      this._setScrollPosition({
        scrollLeft: 0,
        scrollTop: 0
      })
    }

Since nextProps.rowCount === 0, and scrollTop !== 0, _setScrollPosition is setting scrollTop to 0, and now since my scrollTop never changes always staying at a constant number (>0), scrollTop is never set again.

Here is a fiddle: https://jsfiddle.net/omerts/qcrg17md/

[bvaughn]

Ah, you are right about the first issue. I misread (distracted working on something else).

The second check can’t be changed, since scrollTop (and scrollLeft) props are meant to function more as… default values, rather than true controlled props. The change you’ve suggested would cause a List to be snap-locked to the offset specified. (Anytime the state changed in response to a user scroll, the next prop-change would snap it back.)

It’s a bit tricky/unfortunate, but I kind of backed myself into a corner with the API design. ☹️

You can use the API method I mentioned above to work around this or you could refrain from setting scrollTop until the List has some rows. Unfortunately I think those are the only 2 options without a major refactor- so I’m going to close this issue for now. Happy to keep discussing it though.

[bvaughn]

You’re welcome 😄