scroll_snap_list

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

Parameter	Explanation
key	Key for ScrollSnapList, used to call ScrollSnapListState
listViewKey	Key for ListView inside ScrollSnapListState, often used to preserve scroll location
itemBuilder	Same as ListView's itemBuilder
curve	Animation curve when snapping
duration	Animation duration
endOfListTolerance	Pixel tolerance to trigger onReachEnd
focusOnItemTap	Focus to an item when user tap on it. Inactive if the list-item have its own onTap detector (use state-key to help focusing instead).
focusToItem	Method to manually trigger focus to an item. Call with help of GlobalKey<ScrollSnapListState>
margin	Container's margin
itemCount	Number of item in this list
itemSize	Size used is width if scrollDirection is Axis.horizontal, height if Axis.vertical. Composed of the size of each item + its margin/padding.
onItemFocus	Callback function when list snaps/focuses to an item
onReachEnd	Callback function when user reach end of list. E.g. load more data from db
reverse	Same as ListView's reverse to reverse scrollDirection
updateOnScroll	Calls onItemFocus (if it exists) when ScrollUpdateNotification fires
initialIndex	Optional initial position which will not snap until after the first drag
scrollDirection	ListView's scrollDirection
listController	External ScrollController
dynamicItemSize	Scale item's size depending on distance to center
dynamicSizeEquation	Custom equation to determine dynamic item scaling calculation
dynamicItemOpacity	Custom opacity for offset item (single value)
selectedItemAnchor	Anchor location for selected item in the list (Start, Middle, End)
shrinkWrap	ListView's shrinkWrap
scrollPhysics	ListView's scrollPhysics
clipBehavior	ListView's clipBehavior
keyboardDismissBehavior	ListView's keyboardDismissBehavior
allowAnotherDirection	Allow List items to be scrolled using other direction
dispatchScrollNotifications	Control if ScrollNotifications should be dispatched to further ancestors. Default: false

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