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