Fix instance explorer

[micahmo]

Pull Request Description

This PR attempts to fix #1189. I believe the problem is less that the results are cycling endlessly, and more that we are retrieving the same page more than once, causing duplicate results, making it look like a cycle. This seems to be caused by the fact that the scroll trigger can happen multiple times in quick succession, causing the community loading to be re-entrant when we want it to complete (and emit the new page number) before loading more.

Issue Being Fixed

Issue Number: #1189

[hjiangsu]

Ahh I see what's happening here. Could you do something similar to how the FeedPage does it? It checks the bloc's state to see if its currently fetching, and only calls the onScroll logic when its not in the fetching state:

This is the corresponding logic from the FeedPage:

if (
  _scrollController.position.pixels > _scrollController.position.maxScrollExtent * 0.7 &&
  context.read<FeedBloc>().state.status != FeedStatus.fetching
) {
  context.read<FeedBloc>().add(FeedFetchedEvent(
    feedTypeSubview: selectedUserOption[0] ? FeedTypeSubview.post : FeedTypeSubview.comment
  ));
}

[micahmo]

I did that first but that state hadn't updated yet. I'm not sure why _onScroll was being called so quickly in succession, but we can't rely on the bloc to have emitted the loading state yet. Any other ideas?

[hjiangsu]

Hmm, I see. I guess we can stick to the solution you have for the time being!