我正在尝试开发一个TextField,在更改时更新Firestore数据库上的数据。它似乎工作,但我需要防止onChange事件多次触发。
在JS我会使用lodash _debounce()但在Dart中我不知道该怎么做。我已经阅读了一些去抖库但我无法弄清楚它们是如何工作的。
这是我的代码,它只是一个测试,所以有些奇怪的东西:
import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
class ClientePage extends StatefulWidget {
String idCliente;
ClientePage(this.idCliente);
@override
_ClientePageState createState() => new _ClientePageState();
}
class _ClientePageState extends State<ClientePage> {
TextEditingController nomeTextController = new TextEditingController();
void initState() {
super.initState();
// Start listening to changes
nomeTextController.addListener(((){
_updateNomeCliente(); // <- Prevent this function from run multiple times
}));
}
_updateNomeCliente = (){
print("Aggiorno nome cliente");
Firestore.instance.collection('clienti').document(widget.idCliente).setData( {
"nome" : nomeTextController.text
}, merge: true);
}
@override
Widget build(BuildContext context) {
return new StreamBuilder<DocumentSnapshot>(
stream: Firestore.instance.collection('clienti').document(widget.idCliente).snapshots(),
builder: (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
if (!snapshot.hasData) return new Text('Loading...');
nomeTextController.text = snapshot.data['nome'];
return new DefaultTabController(
length: 3,
child: new Scaffold(
body: new TabBarView(
children: <Widget>[
new Column(
children: <Widget>[
new Padding(
padding: new EdgeInsets.symmetric(
vertical : 20.00
),
child: new Container(
child: new Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
new Text(snapshot.data['cognome']),
new Text(snapshot.data['ragionesociale']),
],
),
),
),
new Expanded(
child: new Container(
decoration: new BoxDecoration(
borderRadius: BorderRadius.only(
topLeft: Radius.circular(20.00),
topRight: Radius.circular(20.00)
),
color: Colors.brown,
),
child: new ListView(
children: <Widget>[
new ListTile(
title: new TextField(
style: new TextStyle(
color: Colors.white70
),
controller: nomeTextController,
decoration: new InputDecoration(labelText: "Nome")
),
)
]
)
),
)
],
),
new Text("La seconda pagina"),
new Text("La terza pagina"),
]
),
appBar: new AppBar(
title: Text(snapshot.data['nome'] + ' oh ' + snapshot.data['cognome']),
bottom: new TabBar(
tabs: <Widget>[
new Tab(text: "Informazioni"), // 1st Tab
new Tab(text: "Schede cliente"), // 2nd Tab
new Tab(text: "Altro"), // 3rd Tab
],
),
),
)
);
},
);
print("Il widget id è");
print(widget.idCliente);
}
}
在您的小部件状态中声明一个控制器和计时器:
final _searchQuery = new TextEditingController();
Timer _debounce;
添加一个监听器方法:
_onSearchChanged() {
if (_debounce?.isActive ?? false) _debounce.cancel();
_debounce = Timer(const Duration(milliseconds: 500), () {
// do something with _searchQuery.text
});
}
将方法挂钩并取消挂钩到控制器:
@override
void initState() {
super.initState();
_searchQuery.addListener(_onSearchChanged);
}
@override
void dispose() {
_searchQuery.removeListener(_onSearchChanged);
_searchQuery.dispose();
super.dispose();
}
在构建树中将控制器绑定到TextField:
child: TextField(
controller: _searchQuery,
// ...
)
你可以使用Debouncer
制作Timer
课程
import 'package:flutter/foundation.dart';
import 'dart:async';
class Debouncer {
final int milliseconds;
VoidCallback action;
Timer _timer;
Debouncer({ this.milliseconds });
run(VoidCallback action) {
if (_timer != null) {
_timer.cancel();
}
_timer = Timer(Duration(milliseconds: milliseconds), action);
}
}
宣布它
final _debouncer = Debouncer(milliseconds: 500);
并触发它
onTextChange(String text) {
_debouncer.run(() => print(text));
}
您可以使用rxdart包使用流创建Observable,然后根据您的要求对其进行去抖动。我认为这个link会帮助你开始。
使用rxdart lib中的BehaviorSubject是一个很好的解决方案。它忽略了在前一个X秒内发生的变化。
final searchOnChange = new BehaviorSubject<String>();
...
TextField(onChanged: _search)
...
void _search(String queryString) {
searchOnChange.add(queryString);
}
void initState() {
searchOnChange.debounce(Duration(seconds: 1)).listen((queryString) {
>> request data from your API
});
}
可以使用Future.delayed
方法实现简单的去抖动
bool debounceActive = false;
...
//listener method
onTextChange(String text) async {
if(debounceActive) return null;
debounceActive = true;
await Future.delayed(Duration(milliSeconds:700));
debounceActive = false;
// hit your api here
}