ScrollController not attached to any scroll views

Question

I\'m using CustomScrollView, and providing it with a controller. ScrollController works, I even added a listener to it and print out the position of the scroll view.

Answer 1

This sometimes happens when you are attempting to bind a ScrollController to a widget that doesn't actually exist (yet). So it attempts to bind, but there is no ListView/ScrollView to bind to. Say you have this code:

Column(
  crossAxisAlignment: CrossAxisAlignment.start,
  children: <Widget>[
    Expanded(
      flex: 8,
      child: Container(
        child: ListView.builder(
          controller: scrollController,
          itemCount: messages.length,
          itemBuilder: (context, index) {
            return MessageTile(message: messages[index]);
          }),
        ),
     ),
 ]),

Here we are building a ListView dynamically. Since we never declared this ListView before, the scrollController does not have anything to bind to. But this can easily be fixed:

// first declare the ListView and ScrollController

final scrollController = ScrollController(initialScrollOffset: 0);
ListView list = ListView.builder(
  controller: scrollController,
  itemCount: messages.length,
  itemBuilder: (context, index) {
    return MessageTile(message: messages[index]);
  }
);

// then inside your build function just reference the already built list

Column(
  crossAxisAlignment: CrossAxisAlignment.start,
  children: <Widget>[
    Expanded(
      flex: 8,
      child: Container(
         child: list,
      ),
    ),
  ]),

Answer 2

@carlosx2 answer is correct but if someone wonder where to put WigetsBinding. So here it is.

@override
void initState(){
  super.initState();
  WidgetsBinding.instance.addPostFrameCallback((_){
    //write or call your logic
    //code will run when widget rendering complete
  });
}

Answer 3

Use setState() method to bind to a scroll related widget (your listview etc.)

setState(() {
    topicsScrollController.animateTo(....);
});

Answer 4

Check if the scrollController is attached to a scroll view by using its hasClients property first.

if (_scrollController.hasClients) 
    _scrollController.jumpTo(50.0);

Answer 5

I found working solution, but frankly the method is not best practice, I suppose. In my case controller.jumpTo() was called before it was attached to any scroll view. In order to solve problem I delayed some milliseconds and then call .jumpTo(), because build will be called and controller will be attached to any scroll view.

Future.delayed(Duration(milliseconds: <some time, ex: 100>), () {
         _scrollController.jumpTo(50.0);
        });

I full agree that it is bad solution, but It can solve problem.