如何解决如何在颤振中对特定产品进行递增和递减
我正在开发一个送餐应用程序,我试图为列表中的特定产品创建增量减量系统。一开始它可以工作let deck = [
"r0","r1","r2","r3","r4","r5","r6","r7","r8","r9","rSkip","rReverse","r+2","b0","b1","b2","b3","b4","b5","b6","b7","b8","b9","bSkip","bReverse","b+2","g0","g1","g2","g3","g4","g5","g6","g7","g8","g9","gSkip","gReverse","g+2","y0","y1","y2","y3","y4","y5","y6","y7","y8","y9","ySkip","yReverse","y+2","Wild","Wild+4","Wild+4"
];
function shuffleDeck() {
for (let i = 0; i <= deck.length; i++) {
let randomNum = Math.floor(Math.random() * deck.length);
deck.splice(randomNum,deck[0]);
deck.splice(0,1,deck[randomNum + 1]);
deck.splice(randomNum + 1,1);
}
}
function player() {
this.hand = [];
};
let Player1 = new player();
let Player2 = new player();
let Player3 = new player();
let humanPlayers = [];
//initialize the participants
initializePlayers = prompt("How many players? (1-4)");
if (initializePlayers < 4) {
let initializeString2Num = parseInt(initializePlayers);
for (let j = 0; j <= initializeString2Num - 1; j++) {
//pushing human objects into array
switch (initializePlayers) {
case "1":
humanPlayers.push(Player1);
break;
case "2":
humanPlayers.push(Player2);
break;
case "3":
humanPlayers.push(Player3);
break;
}
}
}
shuffleDeck();
dealCards(humanPlayers.length);
function dealCards(humans) {
console.log("number of humans to deal to " + humanPlayers.length);
switch (humans) {
case 3:
let dealtCard;
console.log("case 3");
for (let l = 0; l <= 7; l++) {
if (l <= 6) {
dealtCard = deck.shift();
}
if (humanPlayers[0].hand.length <= 6) {
humanPlayers[0].hand.push(dealtCard);
console.log(dealtCard);
}
}
for (let m = 0; m <= 7; m++) {
if (m <= 6) {
dealtCard = deck.shift();
}
if (humanPlayers[1].hand.length <= 6) {
humanPlayers[1].hand.push(dealtCard);
console.log(dealtCard);
}
}
for (let n = 0; n <= 7; n++) {
if (n <= 6) {
dealtCard = deck.shift();
}
if (humanPlayers[2].hand.length <= 6) {
humanPlayers[2].hand.push(dealtCard);
console.log(dealtCard);
}
}
break;
}
}
console.log(humanPlayers);
,但是在计数器自动按下i.e the counter increases
之后不久,无需按下任何按钮。我不知道为什么会发生
下面是我正在尝试的代码
这是课程
0
这是从网址获取数据的功能
class ItemData {
final String itemName;
final String itemPrice;
final String image;
int counter = 0;
bool isAdded = false;
ItemData({this.itemName,this.itemPrice,this.image});
}
这是将来的构建器中提取产品的代码
Future<List<ItemData>> _getProducts() async {
var data = await http
.get("https://orangecitycafe.in/app_configs/products_display.php");
var jsonData = json.decode(data.body);
List<ItemData> details = [];
for (var p in jsonData) {
ItemData detail = ItemData(
itemName: p["product_name"],itemPrice: p["product_price"],image: p["product_image"]);
details.add(detail);
}
return details;
}
其余的都起作用,但是只有当我增加计数器时,计数器才会增加,并且在一段时间后它会自动返回到 Widget _myCart() {
return FutureBuilder(
future: _getProfile(),builder: (BuildContext context,AsyncSnapshot snapshot) {
if (snapshot.hasData) {
return ListView.builder(
itemCount: snapshot.data.length,itemBuilder: (BuildContext context,int index) {
return ListTile(
title: Text(snapshot.data[index].itemName),leading: Image.network("https://www.orangecitycafe.in/" +
snapshot.data[index].image),trailing: snapshot.data[index].isAdded
? Row(
mainAxisSize: MainAxisSize.min,children: <Widget>[
IconButton(
icon: Icon(Icons.remove),onPressed: () {
setState(() {
if (snapshot.data[index].counter > 0) {
snapshot.data[index].counter--;
}
});
},color: Colors.green,),Text(snapshot.data[index].counter.toString()),IconButton(
icon: Icon(Icons.add),onPressed: () {
setState(() {
snapshot.data[index].counter++;
});
},],)
: RaisedButton(
onPressed: (){
setState(() {
snapshot.data[index].isAdded = true;
});
},child: Text("Add"),);
},);
} else {
return Container();
}
},);
}
解决方法
您可以在下面复制粘贴运行完整代码
您可以使用以下方式在Future
中使用FutureBuilder
,以避免setState
导致FutureBuilder
再次重建。
详细原因https://github.com/flutter/flutter/issues/11426#issuecomment-414047398
每次发出重建文件时,都会调用didUpdateWidget
状态的FutureBuilder
。此函数检查旧的旧对象是否与新的旧对象不同,如果有,则重新触发FutureBuilder
。
要克服这一点,我们可以在构建函数之外的其他地方调用Future
。例如,在initState
中,将其保存在成员变量中,然后将此变量传递给FutureBuilder
。
代码段
Future<List<ItemData>> _future;
...
@override
void initState() {
_future = _getProducts();
super.initState();
}
...
Widget _myCart() {
return FutureBuilder(
future: _future,
工作演示
完整代码
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';
class ItemData {
final String itemName;
final String itemPrice;
final String image;
int counter = 0;
bool isAdded = false;
ItemData({this.itemName,this.itemPrice,this.image});
}
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',theme: ThemeData(
primarySwatch: Colors.blue,visualDensity: VisualDensity.adaptivePlatformDensity,),home: MyHomePage(title: 'Flutter Demo Home Page'),);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key,this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
Future<List<ItemData>> _future;
Future<List<ItemData>> _getProducts() async {
var data = await http
.get("https://orangecitycafe.in/app_configs/products_display.php");
var jsonData = json.decode(data.body);
List<ItemData> details = [];
for (var p in jsonData) {
ItemData detail = ItemData(
itemName: p["product_name"],itemPrice: p["product_price"],image: p["product_image"]);
details.add(detail);
}
return details;
}
@override
void initState() {
_future = _getProducts();
super.initState();
}
Widget _myCart() {
return FutureBuilder(
future: _future,builder: (BuildContext context,AsyncSnapshot snapshot) {
if (snapshot.hasData) {
return ListView.builder(
itemCount: snapshot.data.length,itemBuilder: (BuildContext context,int index) {
return ListTile(
title: Text(snapshot.data[index].itemName),leading: Image.network("https://www.orangecitycafe.in/" +
snapshot.data[index].image),trailing: snapshot.data[index].isAdded
? Row(
mainAxisSize: MainAxisSize.min,children: <Widget>[
IconButton(
icon: Icon(Icons.remove),onPressed: () {
setState(() {
if (snapshot.data[index].counter > 0) {
snapshot.data[index].counter--;
}
});
},color: Colors.green,Text(snapshot.data[index].counter.toString()),IconButton(
icon: Icon(Icons.add),onPressed: () {
setState(() {
snapshot.data[index].counter++;
});
},],)
: RaisedButton(
onPressed: () {
setState(() {
snapshot.data[index].isAdded = true;
});
},child: Text("Add"),);
},);
} else {
return Container();
}
},);
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),body: _myCart());
}
}
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