"filterSearchResults"中 else 部分的 setstate 中的"data"值正在获取空值

Question

"filterSearchResults"中else部分的setstate中的"data"值为空。数据值是我从上一页传递的值。

我在变量数据中得到一个空值，作为"filterSearchResults"函数中else部分的setstate。

import 'package:flutter/material.dart';
class Country extends StatefulWidget {
final List data;
Country(this.data);
@override
_CountryState createState() => _CountryState(this.data);
}
class _CountryState extends State<Country> {
TextEditingController editingController = TextEditingController();
List data;
_CountryState(this.data);
List data1;
//  search function
void filterSearchResults(String query) {
List<dynamic> dummySearchList = List<dynamic>();
List<dynamic> dummyList = List<dynamic>();
dummySearchList.addAll(data1);
print("dummy sreach List : $dummySearchList");
if (query.isNotEmpty) {
for (var i = 0; i < data1.length; i++) {
var keys = data1[i].keys.toList();
var val = data1[i][keys[0]];
print("val is: ${val.toLowerCase()}");
if (val.toLowerCase().contains((query.toLowerCase()))) {
dummyList.add(data1[i]);
print("dummy list is : $dummyList");
}
}
setState(() {
print("if set");
data1.clear();
data1 = dummyList;
print("data1 : $data1");
});
return;
} else {
print("else started");
setState(() {
data1.clear();
print("CLEAR DATA : $data1");
print('original data: $data'); 
data1 = data;                     //this is where the problem is.. 
print('else data1: $data1');
print("else ended");
});
}
}
void setData1() {
setState(() {
this.data1 = data;
print("set data : $data");
});
}
@override
void initState() {
super.initState();
setData1();
print("init state started");
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Covid 19"),
),
body: Container(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
TextField(
controller: editingController,
decoration: InputDecoration(
labelText: "Search",
hintText: "Search",
prefixIcon: Icon(Icons.search),
border: OutlineInputBorder(
borderRadius: BorderRadius.all(Radius.circular(25.0)))),
onChanged: (value) {
filterSearchResults(value);
},
),
Expanded(
child: ListView.builder(
itemCount: data1.length,
shrinkWrap: true,
itemBuilder: (context, index) {
Padding(padding: EdgeInsets.fromLTRB(8, 5, 8, 5));
return Card(
elevation: 5,
child: Container(
height: 200,
width: MediaQuery.of(context).size.width,
child: Column(
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
Padding(
padding: EdgeInsets.only(top: 10),
),
Text(
data1[index]['country'],
style: TextStyle(fontSize: 30, color: Colors.black),
),
Padding(
padding: EdgeInsets.only(top: 20),
),
Row(
children: <Widget>[
Expanded(
child: Column(
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
Text(
"Cases",
style: TextStyle(
fontSize: 15, color: Colors.black),
),
Text(
data1[index]["cases"].toString(),
style: TextStyle(
fontSize: 15, color: Colors.black),
),
Padding(
padding: EdgeInsets.only(top: 25),
),
Text(
"TodayCases",
style: TextStyle(
fontSize: 15, color: Colors.black),
),
Text(
data1[index]["todayCases"].toString(),
style: TextStyle(
fontSize: 15, color: Colors.black),
),
],
),
),
Expanded(
child: Column(
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
Text(
"Deaths",
style: TextStyle(
fontSize: 15, color: Colors.black),
),
Text(
data1[index]["deaths"].toString(),
style: TextStyle(
fontSize: 15, color: Colors.black),
),
Padding(
padding: EdgeInsets.only(top: 25),
),
Text(
"TodayDeaths",
style: TextStyle(
fontSize: 15, color: Colors.black),
),
Text(
data1[index]["todayDeaths"].toString(),
style: TextStyle(
fontSize: 15, color: Colors.black),
),
],
),
),
Expanded(
child: Column(
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
Text(
"Active",
style: TextStyle(
fontSize: 15, color: Colors.black),
),
Text(
data1[index]["active"].toString(),
style: TextStyle(
fontSize: 15, color: Colors.black),
),
Padding(
padding: EdgeInsets.only(top: 25),
),
Text(
"Recovered",
style: TextStyle(
fontSize: 15, color: Colors.black),
),
Text(
data1[index]["recovered"].toString(),
style: TextStyle(
fontSize: 15, color: Colors.black),
),
],
),
),
Expanded(
child: Column(
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
Text(
"Critical",
style: TextStyle(
fontSize: 15, color: Colors.black),
),
Text(
data1[index]["critical"].toString(),
style: TextStyle(
fontSize: 15, color: Colors.black),
),
Padding(
padding: EdgeInsets.only(top: 25),
),
Text(
"PerOneMillion",
style: TextStyle(
fontSize: 15, color: Colors.black),
),
Text(
data1[index]["casesPerOneMillion"]
.toString(),
style: TextStyle(
fontSize: 15, color: Colors.black),
),
],
),
),
],
),
],
),
),
);
},
),
),
],
),
),
);
}
}

Answer 1

您必须从widget字段访问data字段：this.widget.data。通过State传递数据不会被更新。请参阅将数据传递到状态小部件

尝试将StatefulWidget更改为：

class Country extends StatefulWidget {
final List data;
const Country ({Key key, this.data}): super(key: key);
@override
_CountryState createState() => _CountryState();
}
class _CountryState extends State<Country> {
TextEditingController editingController = TextEditingController();
List data1;
...

在您的其他部分，您必须访问数据变量，然后通过widget.data

else {
print("else started");
setState(() {
data1.clear();
print("CLEAR DATA : $data1");
print('original data: $widget.data');
data1 = widget.data; //this is where the problem (hopefully) were..
print('else data1: $data1');
print("else ended");
}