scroll_snap_list #

A wrapper for ListView.builder widget that allows "snaping" event to an item at the end of user-scroll.

This widget allows unrestricted scrolling (unlike other widget that only able to "snap" to left/right neighbor at a time).

• Support horizontal & vertical list
• Use ListView.Builder, means no Animation

You can use this widget to achieve:

• Unrestricted scrollable Jumbotron
• Show daily entry for Health App and shows its detail directly below the list (reduce number of click)
• Scrollable InputSelect, like datetime picker in cupertino

Horizontal Jumbotron List	Horizontal List with infinite-loading	Vertical list with InkWell ListItems	Horizontal with dynamic item size	Horizontal with custom dynamic item size

Getting Started #

In your flutter project pubspec.yaml add the dependency:

dependencies:
  ...
  scroll_snap_list: ^[version]

Usage example #

This library doesn't use other library, so it should work out of the box.

Import scroll_snap_list.dart.

import 'package:scroll_snap_list/scroll_snap_list.dart';

Add ScrollSnapList in your build method. Make sure to enter correct itemSize (helps with "snapping" process).

Expanded(
  child: ScrollSnapList(
    onItemFocus: _onItemFocus,
    itemSize: 35,
    itemBuilder: _buildListItem,
    itemCount: data.length,
    reverse: true,
  ),
),

Full example:

import 'dart:math';

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

void main() => runApp(HorizontalListDemo());

class HorizontalListDemo extends StatefulWidget {
  @override
  _HorizontalListDemoState createState() => _HorizontalListDemoState();
}

class _HorizontalListDemoState extends State<HorizontalListDemo> {
  List<int> data = [];
  int _focusedIndex = 0;

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

    for (int i = 0; i < 30; i++) {
      data.add(Random().nextInt(100) + 1);
    }
  }

  void _onItemFocus(int index) {
    setState(() {
      _focusedIndex = index;
    });
  }

  Widget _buildItemDetail() {
    if (data.length > _focusedIndex)
      return Container(
        height: 150,
        child: Text("index $_focusedIndex: ${data[_focusedIndex]}"),
      );

    return Container(
      height: 150,
      child: Text("No Data"),
    );
  }

  Widget _buildListItem(BuildContext context, int index) {
    //horizontal
    return Container(
      width: 35,
      child: Column(
        mainAxisAlignment: MainAxisAlignment.end,
        children: <Widget>[
          Container(
            height: data[index].toDouble()*2,
            width: 25,
            color: Colors.lightBlueAccent,
            child: Text("i:$index\n${data[index]}"),
          )
        ],
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Horizontal List Demo',
      home: Scaffold(
        appBar: AppBar(
          title: Text("Horizontal List"),
        ),
        body: Container(
          child: Column(
            children: <Widget>[
              Expanded(
                child: ScrollSnapList(
                  onItemFocus: _onItemFocus,
                  itemSize: 35,
                  itemBuilder: _buildListItem,
                  itemCount: data.length,
                  reverse: true,
                ),
              ),
              _buildItemDetail(),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                children: <Widget>[
                  RaisedButton(
                    child: Text("Add Item"),
                    onPressed: () {
                      setState(() {
                        data.add(Random().nextInt(100) + 1);
                      });
                    },
                  ),
                  RaisedButton(
                    child: Text("Remove Item"),
                    onPressed: () {
                      int index = data.length > 1
                          ? Random().nextInt(data.length - 1)
                          : 0;
                      setState(() {
                        data.removeAt(index);
                      });
                    },
                  ),
                ],
              )
            ],
          ),
        ),
      ),
    );
  }
}

Usage with dynamic item size #

This feature is added since version 0.4.0.

We can customize item size with respect to distance between item and center of ScrollSnapList.

@override
Widget build(BuildContext context) {
  return MaterialApp(
    title: 'Horizontal List Demo',
    home: Scaffold(
      appBar: AppBar(
        title: Text("Horizontal List"),
      ),
      body: Container(
        child: Column(
          children: <Widget>[
            Expanded(
              child: ScrollSnapList(
                onItemFocus: _onItemFocus,
                itemSize: 150,
                itemBuilder: _buildListItem,
                itemCount: data.length,
                dynamicItemSize: true,
                // dynamicSizeEquation: customEquation, //optional
              ),
            ),
            _buildItemDetail(),
          ],
        ),
      ),
    ),
  );
}

Important parameters and explanation #

Other Notice #

By default, SnapScrollList set focusOnItemTap as true. Means any tap event on items will trigger snap/focus event to that item.

This behavior use GestureDetector, so if the list's items have their own detector (e.g. InkWell, Button), SnapScrollList unable to trigger snap event on its own. To handle this, we may use GlobalKey<ScrollSnapListState> to trigger the event manually.

Add GlobalKey<ScrollSnapListState> in your widget

GlobalKey<ScrollSnapListState> sslKey = GlobalKey();

Add key parameter to SnapScrollList.

ScrollSnapList(
  onItemFocus: _onItemFocus,
  itemSize: 50,
  itemBuilder: _buildListItem,
  itemCount: data.length,
  key: sslKey,
  scrollDirection: Axis.vertical,
)

In your buildItem method, call focusToItem method.

Widget _buildListItem(BuildContext context, int index) {
  //horizontal
  return Container(
    height: 50,
    child: Material(
      color: _focusedIndex == index ? Colors.lightBlueAccent : Colors.white,
      child: InkWell(
        child: Text("Index: $index | Value: ${data[index]}"),
        onTap: () {
          print("Do anything here");

          //trigger focus manually
          sslKey.currentState.focusToItem(index);
        },
      ),
    ),
  );
}

Full example for this part can be found in example/vertical_list.dart.

About #

Created by Vincent (MSVCode) Email: msvcode@gmail.com