how to await setState in Flutter?

Question

I am dynamically adding item to ListView. When I add new item, it should scroll to bottom like in WhatsApp app.

I am doing it like this

setState(() {
  _textList.add(text);
});
_scrollController.animateTo( //Should run after rebuild
  _scrollController.position.maxScrollExtent,
  duration: const Duration(milliseconds: 300),
  curve: Curves.easeInOut,
);

Since setState() runs asynchronously, maxScrollExtent is not updated, which is resulting in scroll until previous item only.

How to do await for setState. Is there anyway to achieve this. Also I don't want do call Future.delayed.

Here is my full code DartPad.

Thanks.

use scrollcontroller not set state to dynamically scroll to positions. what about this https://stackoverflow.com/questions/47916247/flutter-scroll-to-bottom-of-dynamic-listview ? — Salma, Dec 23 '19 at 14:06
`WidgetsBinding.instance..addPostFrameCallback` is what I actually wanted like @HarshvardhanJoshi mentioned. But there is a new problem by using it, I am trying to solve it. Thanks @Salma. — Crazy Lazy Cat, Dec 23 '19 at 14:20
SetState is synchronous, so the whole question doesn't make sense — Rémi Rousselet, Dec 23 '19 at 14:32
@HarshvardhanJoshi If I add `_scrollController.animateTo` as call back in `addPostFrameCallback`, it scrolls once. But my `ListView` is lazily build. — Crazy Lazy Cat, Dec 23 '19 at 14:46
@HarshvardhanJoshi Important: I only want it to scroll to bottom when i send message, not when receive message. So I did not use it inside `build` — Crazy Lazy Cat, Dec 23 '19 at 14:51
@CrazyLazyCat you should use this code when sending message. As in somewhere where you trigger an event for sending message. Like, side onTap of the send button — Harshvardhan Joshi, Dec 23 '19 at 14:57
@HarshvardhanJoshi that is what I did. The problem is solved. Because of the debug mode, it looked like jumping around. It works good in performance mode. Thank you so much — Crazy Lazy Cat, Dec 23 '19 at 15:46
Don't do close vote with another post that is not even related to this topic. At least see the tags attached — Crazy Lazy Cat, Dec 24 '19 at 05:22
@RémiRousselet Atleast some people understood the problem and gave the answer — Crazy Lazy Cat, Dec 24 '19 at 05:43

score 0 · Answer 1 · answered Dec 23 '19 at 15:35

You can try this method as the first line in your build method.

         WidgetsBinding.instance.addPostFrameCallback((_) {
                  if (_scrollController.hasClients) {
                    _scrollController.animateTo( 
      _scrollController.position.maxScrollExtent,
      duration: const Duration(milliseconds: 300),
      curve: Curves.easeInOut,
    );
  }

  });

how to await setState in Flutter?

1 Answers1