Flutter：滚动到 ListView 中的小部件

Question

How can I scroll to a special widget in a ListView ? For instance I want to scroll automatically to some Container in the ListView if I press a specific button.

ListView(children: <Widget>[
  Container(...),
  Container(...), #scroll for example to this container 
  Container(...)
]);

Answer 1

By far, the easiest solution is to use Scrollable.ensureVisible(context) . As it does everything for you and work with any widget size. Fetching the context using GlobalKey .

The problem is that ListView won't render non-visible items. Meaning that your target most likely will not be built at all . Which means your target will have no context ; preventing you from using that method without some more work.

In the end, the easiest solution will be to replace your ListView by a SingleChildScrollView and wrap your children into a Column . Example :

class ScrollView extends StatelessWidget {
  final dataKey = new GlobalKey();

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      primary: true,
      appBar: new AppBar(
        title: const Text('Home'),
      ),
      body: new SingleChildScrollView(
        child: new Column(
          children: <Widget>[
            new SizedBox(height: 160.0, width: double.infinity, child: new Card()),
            new SizedBox(height: 160.0, width: double.infinity, child: new Card()),
            new SizedBox(height: 160.0, width: double.infinity, child: new Card()),
            // destination
            new Card(
              key: dataKey,
              child: new Text("data\n\n\n\n\n\ndata"),
            )
          ],
        ),
      ),
      bottomNavigationBar: new RaisedButton(
        onPressed: () => Scrollable.ensureVisible(dataKey.currentContext),
        child: new Text("Scroll to data"),
      ),
    );
  }
}

NOTE : While this allows to scroll to the desired item easily, consider this method only for small predefined lists. As for bigger lists you'll get performance problems.

But it's possible to make Scrollable.ensureVisible work with ListView ; although it will require more work.

Answer 2

Unfortunately, ListView has no built-in approach to a scrollToIndex() function. You'll have to develop your own way to measure to that element's offset for animateTo() or jumpTo() , or you can search through these suggested solutions/plugins or from other posts like flutter ListView scroll to index not available

(the general scrollToIndex issue is discussed at flutter/issues/12319 since 2017, but still with no current plans)

---

But there is a different kind of ListView that does support scrollToIndex:

• ScrollablePositionedList
  • dependency: scrollable_positioned_list

You set it up exactly like ListView and works the same, except you now have access to a ItemScrollController that does:

• jumpTo({index, alignment})
• scrollTo({index, alignment, duration, curve})

Simplified example:

ItemScrollController _scrollController = ItemScrollController();

ScrollablePositionedList.builder(
  itemScrollController: _scrollController,
  itemCount: _myList.length,
  itemBuilder: (context, index) {
    return _myList[index];
  },
)

_scrollController.scrollTo(index: 150, duration: Duration(seconds: 1));

(note that this library is developed by Google but not by the core Flutter team.)

Answer 3

If your widgets inside the ListView all have the same height, you can implement it like this:

Screenshot:

---

For ListView , you can try this, the following code will animate to 10th index.

class HomePage extends StatelessWidget {
  final _controller = ScrollController();
  final _height = 100.0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      floatingActionButton: FloatingActionButton(
        onPressed: () => _animateToIndex(10),
        child: Icon(Icons.arrow_downward),
      ),
      body: ListView.builder(
        controller: _controller,
        itemCount: 100,
        itemBuilder: (_, i) => Container(
          height: _height,
          child: Card(child: Center(child: Text("Item $i"))),
        ),
      ),
    );
  }

  _animateToIndex(i) => _controller.animateTo(_height * i, duration: Duration(seconds: 2), curve: Curves.fastOutSlowIn);
}

Answer 4

For people are trying to jump to widget in CustomScrollView . First, add this plugin to your project.

Then look at my example code below:

class Example extends StatefulWidget {
  @override
  _ExampleState createState() => _ExampleState();
}

class _ExampleState extends State<Example> {
  AutoScrollController _autoScrollController;
  final scrollDirection = Axis.vertical;

  bool isExpaned = true;
  bool get _isAppBarExpanded {
    return _autoScrollController.hasClients &&
        _autoScrollController.offset > (160 - kToolbarHeight);
  }

  @override
  void initState() {
    _autoScrollController = AutoScrollController(
      viewportBoundaryGetter: () =>
          Rect.fromLTRB(0, 0, 0, MediaQuery.of(context).padding.bottom),
      axis: scrollDirection,
    )..addListener(
        () => _isAppBarExpanded
            ? isExpaned != false
                ? setState(
                    () {
                      isExpaned = false;
                      print('setState is called');
                    },
                  )
                : {}
            : isExpaned != true
                ? setState(() {
                    print('setState is called');
                    isExpaned = true;
                  })
                : {},
      );
    super.initState();
  }

  Future _scrollToIndex(int index) async {
    await _autoScrollController.scrollToIndex(index,
        preferPosition: AutoScrollPosition.begin);
    _autoScrollController.highlight(index);
  }

  Widget _wrapScrollTag({int index, Widget child}) {
    return AutoScrollTag(
      key: ValueKey(index),
      controller: _autoScrollController,
      index: index,
      child: child,
      highlightColor: Colors.black.withOpacity(0.1),
    );
  }

  _buildSliverAppbar() {
    return SliverAppBar(
      brightness: Brightness.light,
      pinned: true,
      expandedHeight: 200.0,
      backgroundColor: Colors.white,
      flexibleSpace: FlexibleSpaceBar(
        collapseMode: CollapseMode.parallax,
        background: BackgroundSliverAppBar(),
      ),
      bottom: PreferredSize(
        preferredSize: Size.fromHeight(40),
        child: AnimatedOpacity(
          duration: Duration(milliseconds: 500),
          opacity: isExpaned ? 0.0 : 1,
          child: DefaultTabController(
            length: 3,
            child: TabBar(
              onTap: (index) async {
                _scrollToIndex(index);
              },
              tabs: List.generate(
                3,
                (i) {
                  return Tab(
                    text: 'Detail Business',
                  );
                },
              ),
            ),
          ),
        ),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        controller: _autoScrollController,
        slivers: <Widget>[
          _buildSliverAppbar(),
          SliverList(
              delegate: SliverChildListDelegate([
            _wrapScrollTag(
                index: 0,
                child: Container(
                  height: 300,
                  color: Colors.red,
                )),
            _wrapScrollTag(
                index: 1,
                child: Container(
                  height: 300,
                  color: Colors.red,
                )),
            _wrapScrollTag(
                index: 2,
                child: Container(
                  height: 300,
                  color: Colors.red,
                )),
          ])),
        ],
      ),
    );
  }
}

Yeah it's just a example, use your brain to make it this idea become true

Answer 5

You can just specify a ScrollController to your listview and call the animateTo method on button click.

A mininmal example to demonstrate animateTo usage :

class Example extends StatefulWidget {
  @override
  _ExampleState createState() => new _ExampleState();
}

class _ExampleState extends State<Example> {
  ScrollController _controller = new ScrollController();

  void _goToElement(int index){
    _controller.animateTo((100.0 * index), // 100 is the height of container and index of 6th element is 5
        duration: const Duration(milliseconds: 300),
        curve: Curves.easeOut);
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(),
      body: new Column(
        children: <Widget>[
          new Expanded(
            child: new ListView(
              controller: _controller,
              children: Colors.primaries.map((Color c) {
                return new Container(
                  alignment: Alignment.center,
                  height: 100.0,
                  color: c,
                  child: new Text((Colors.primaries.indexOf(c)+1).toString()),
                );
              }).toList(),
            ),
          ),
          new FlatButton(
            // on press animate to 6 th element
            onPressed: () => _goToElement(6),
            child: new Text("Scroll to 6th element"),
          ),
        ],
      ),
    );
  }
}

Answer 6

Output:

Use Dependency:

dependencies:
    scroll_to_index: ^1.0.6

Code: (Scroll will always perform 6th index widget as its added below as hardcoded, try with scroll index which you required for scrolling to specific widget)

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final scrollDirection = Axis.vertical;

  AutoScrollController controller;
  List<List<int>> randomList;

  @override
  void initState() {
    super.initState();
    controller = AutoScrollController(
        viewportBoundaryGetter: () =>
            Rect.fromLTRB(0, 0, 0, MediaQuery.of(context).padding.bottom),
        axis: scrollDirection);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: ListView(
        scrollDirection: scrollDirection,
        controller: controller,
        children: <Widget>[
          ...List.generate(20, (index) {
            return AutoScrollTag(
              key: ValueKey(index),
              controller: controller,
              index: index,
              child: Container(
                height: 100,
                color: Colors.red,
                margin: EdgeInsets.all(10),
                child: Center(child: Text('index: $index')),
              ),
              highlightColor: Colors.black.withOpacity(0.1),
            );
          }),
        ],
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _scrollToIndex,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
  // Scroll listview to the sixth item of list, scrollling is dependent on this number
  Future _scrollToIndex() async {
    await controller.scrollToIndex(6, preferPosition: AutoScrollPosition.begin);
  }
}

Answer 7

I found a perfect solution to it using ListView .
I forgot where the solution comes from, so I posted my code. This credit belongs to other one.

21/09/22:edit. I posted a complete example here, hope it is clearer.

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

class CScrollToPositionPage extends StatefulWidget {

CScrollToPositionPage();

@override
State<StatefulWidget> createState() => CScrollToPositionPageState();
}

class CScrollToPositionPageState extends State<CScrollToPositionPage> {
static double TEXT_ITEM_HEIGHT = 80;
final _formKey = GlobalKey<FormState>();
late List _controls;
List<FocusNode> _lstFocusNodes = [];

final __item_count = 30;

@override
void initState() {
    super.initState();

    _controls = [];
    for (int i = 0; i < __item_count; ++i) {
        _controls.add(TextEditingController(text: 'hello $i'));

        FocusNode fn = FocusNode();
        _lstFocusNodes.add(fn);
        fn.addListener(() {
            if (fn.hasFocus) {
                _ensureVisible(i, fn);
            }
        });
    }
}

@override
void dispose() {
    super.dispose();

    for (int i = 0; i < __item_count; ++i) {
        (_controls[i] as TextEditingController).dispose();
    }
}

@override
Widget build(BuildContext context) {
    List<Widget> widgets = [];
    for (int i = 0; i < __item_count; ++i) {
        widgets.add(TextFormField(focusNode: _lstFocusNodes[i],controller: _controls[i],));
    }

    return Scaffold( body: Container( margin: const EdgeInsets.all(8),
        height: TEXT_ITEM_HEIGHT * __item_count,
        child: Form(key: _formKey, child: ListView( children: widgets)))
    );
}

Future<void> _keyboardToggled() async {
    if (mounted){
        EdgeInsets edgeInsets = MediaQuery.of(context).viewInsets;
        while (mounted && MediaQuery.of(context).viewInsets == edgeInsets) {
            await Future.delayed(const Duration(milliseconds: 10));
        }
    }

    return;
}
Future<void> _ensureVisible(int index,FocusNode focusNode) async {
    if (!focusNode.hasFocus){
        debugPrint("ensureVisible. has not the focus. return");
        return;
    }

    debugPrint("ensureVisible. $index");
    // Wait for the keyboard to come into view
    await Future.any([Future.delayed(const Duration(milliseconds: 300)), _keyboardToggled()]);


    var renderObj = focusNode.context!.findRenderObject();
    if( renderObj == null ) {
      return;
    }
    var vp = RenderAbstractViewport.of(renderObj);
    if (vp == null) {
        debugPrint("ensureVisible. skip. not working in Scrollable");
        return;
    }
    // Get the Scrollable state (in order to retrieve its offset)
    ScrollableState scrollableState = Scrollable.of(focusNode.context!)!;

    // Get its offset
    ScrollPosition position = scrollableState.position;
    double alignment;

    if (position.pixels > vp.getOffsetToReveal(renderObj, 0.0).offset) {
        // Move down to the top of the viewport
        alignment = 0.0;
    } else if (position.pixels < vp.getOffsetToReveal(renderObj, 1.0).offset){
        // Move up to the bottom of the viewport
        alignment = 1.0;
    } else {
        // No scrolling is necessary to reveal the child
        debugPrint("ensureVisible. no scrolling is necessary");
        return;
    }

    position.ensureVisible(
        renderObj,
        alignment: alignment,
        duration: const Duration(milliseconds: 300),
    );

}

}

Answer 8

Here is the solution for StatefulWidget if you want to made widget visible right after building the view tree .

By extending Remi's answer, you can achieve it with this code:

class ScrollView extends StatefulWidget {
  // widget init
}

class _ScrollViewState extends State<ScrollView> {

  final dataKey = new GlobalKey();

  // + init state called

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      primary: true,
      appBar: AppBar(
        title: const Text('Home'),
      ),
      body: _renderBody(),
    );
  }

  Widget _renderBody() {
    var widget = SingleChildScrollView(
        child: Column(
          children: <Widget>[
           SizedBox(height: 1160.0, width: double.infinity, child: new Card()),
           SizedBox(height: 420.0, width: double.infinity, child: new Card()),
           SizedBox(height: 760.0, width: double.infinity, child: new Card()),
           // destination
           Card(
              key: dataKey,
              child: Text("data\n\n\n\n\n\ndata"),
            )
          ],
        ),
      );
    setState(() {
        WidgetsBinding.instance!.addPostFrameCallback(
              (_) => Scrollable.ensureVisible(dataKey.currentContext!));
    });
    return widget;
  }
}

Answer 9

I am posting a solution here in which List View will scroll 100 pixel right and left . you can change the value according to your requirements. It might be helpful for someone who want to scroll list in both direction

import 'package:flutter/material.dart';

class HorizontalSlider extends StatelessWidget {
 HorizontalSlider({Key? key}) : super(key: key);

// Dummy Month name
List<String> monthName = [
"Jan",
"Feb",
"Mar",
"Apr",
"May",
"Jun",
"July",
"Aug",
"Sep",
"Oct",
"Nov",
"Dec"
 ];
ScrollController slideController = new ScrollController();

@override
Widget build(BuildContext context) {
 return Container(
  child: Flex(
    direction: Axis.horizontal,
    crossAxisAlignment: CrossAxisAlignment.center,
    mainAxisAlignment: MainAxisAlignment.center,
    children: [
      InkWell(
        onTap: () {
          // Here monthScroller.position.pixels represent current postion 
          // of scroller
           slideController.animateTo(
            slideController.position.pixels - 100, // move slider to left
             duration: Duration(
              seconds: 1,
            ),
            curve: Curves.ease,
          );
        },
        child: Icon(Icons.arrow_left),
      ),
      Container(
        height: 50,
        width: MediaQuery.of(context).size.width * 0.7,
        child: ListView(
          scrollDirection: Axis.horizontal,
          controller: slideController,
          physics: ScrollPhysics(),
          children: monthName
              .map((e) => Padding(
                    padding: const EdgeInsets.all(12.0),
                    child: Text("$e"),
                  ))
              .toList(),
        ),
      ),
      GestureDetector(
        onTap: () {
          slideController.animateTo(
            slideController.position.pixels +
                100, // move slider 100px to right
            duration: Duration(
              seconds: 1,
            ),
            curve: Curves.ease,
          );
        },
        child: Icon(Icons.arrow_right),
      ),
    ],
  ),
);
 }
 }

Answer 10

You can use GlobalKey to access buildercontext.

I use GlobalObjectKey with Scrollable .

Define GlobalObjectKey in item of ListView

ListView.builder(
itemCount: category.length,
itemBuilder: (_, int index) {
return Container(
    key: GlobalObjectKey(category[index].id),

You can navigate to item from anywhere

InkWell(
  onTap: () {
Scrollable.ensureVisible(GlobalObjectKey(category?.id).currentContext);

You add scrollable animation changing property of ensureVisible

Scrollable.ensureVisible(
  GlobalObjectKey(category?.id).currentContext,
  duration: Duration(seconds: 1),// duration for scrolling time
  alignment: .5, // 0 mean, scroll to the top, 0.5 mean, half
  curve: Curves.easeInOutCubic);

Answer 11

You can also simply use the FixedExtentScrollController for same size items with the index of your initialItem :

controller: FixedExtentScrollController(initialItem: itemIndex);

The documentation : Creates a scroll controller for scrollables whose items have the same size.

Answer 12

The simplest way is to call this method inside your InitState method. (not the build to evict unwanted errors)

WidgetsBinding.instance.addPostFrameCallback((_) => Scrollable.ensureVisible(targetKey.currentContext!))

WidgetsBinding.instance.addPostFrameCallback will guarantee that the list is builded and the this automatic search for your target and move the scroll to it. You can then customize the animation of the scroll effect on the Scrollable.ensureVisible method

Note: Remember to add the targetKey (a GlobalKey ) to the widget you want to scroll to.

Answer 13

Adding with Rémi Rousselet's answer,

If there is a case you need to scroll past to end scroll position with addition of keyboard pop up, this might be hided by the keyboard . Also you might notice the scroll animation is a bit inconsistent when keyboard pops up (there is addition animation when keyboard pops up), and sometimes acts weird. In that case wait till the keyboard finishes animation(500ms for ios).

BuildContext context = key.currentContext;
  Future.delayed(const Duration(milliseconds: 650), () {
    Scrollable.of(context).position.ensureVisible(
        context.findRenderObject(),
        duration: const Duration(milliseconds: 600));
  });

Answer 14

1. To achieve initial scrolling at a particular index in a list of items
2. on tap of the floating action button you will be scrolled to an index of 10 in a list of items

    class HomePage extends StatelessWidget {
      final _controller = ScrollController();
      final _height = 100.0;
    
      @override
      Widget build(BuildContext context) {
        
        // to achieve initial scrolling at particular index
        SchedulerBinding.instance.addPostFrameCallback((_) {
          _scrollToindex(20);
        });
    
        return Scaffold(
          appBar: AppBar(),
          floatingActionButton: FloatingActionButton(
            onPressed: () => _scrollToindex(10),
            child: Icon(Icons.arrow_downward),
          ),
          body: ListView.builder(
            controller: _controller,
            itemCount: 100,
            itemBuilder: (_, i) => Container(
              height: _height,
              child: Card(child: Center(child: Text("Item $i"))),
            ),
          ),
        );
      }
    // on tap, scroll to particular index
      _scrollToindex(i) => _controller.animateTo(_height * i,
          duration: Duration(seconds: 2), curve: Curves.fastOutSlowIn);
    }

Answer 15

This solution improves upon other answers as it does not require hard-coding each elements' heights. Adding ScrollPosition.viewportDimension<\/code> and ScrollPosition.maxScrollExtent<\/code> yields the full content height. This can be used to estimate the position of an element at some index. If all elements are the same height, the estimation is perfect.

// Get the full content height.
final contentSize = controller.position.viewportDimension + controller.position.maxScrollExtent;
// Index to scroll to.
final index = 100;
// Estimate the target scroll position.
final target = contentSize * index / itemCount;
// Scroll to that position.
controller.position.animateTo(
  target,
  duration: const Duration(seconds: 2),
  curve: Curves.easeInOut,
);

Answer 16

这些答案不会使您的列表默认集中在底部，我使用了这个技巧希望它有所帮助：首先反转您提供给ListView.builder的列表，然后将此属性添加到您的 ListView ： reverse: true

Answer 17

Simply use page view controller. Example:

   var controller = PageController();  
     
    ListView.builder(
      controller: controller,
      itemCount: 15,
      itemBuilder: (BuildContext context, int index) {
       return children[index);
      },
    ),
     ElevatedButton(
            onPressed: () {
              controller.animateToPage(5,   //any index that you want to go
    duration: Duration(milliseconds: 700), curve: Curves.linear);
              },
            child: Text(
              "Contact me",), 

       

Answer 18

您可以在加载完成后使用 controller.jumpTo(100)