如何解决根据对象列表的排序方式对字符串列表进行排序
我遇到了问题,我试图根据对象列表的排序方式对字符串列表进行排序。
这是我的代码:
void main() => runApp(MaterialApp(home: App()));
List<objects> items = List<objects>();
List<String> filteritems = List();
class App extends StatefulWidget {
@override
_AppState createState() => _AppState();
}
class _AppState extends State<App> {
void berechnung() {
for (var i = 0; i < items.length; i++) {
items[i].result = items[i].number1 + items[i].number2;
}
final Map<String,String> mappings = {
for (int i = 0; i < items.length; i++)
items[i].title : filteritems[i]
};
Comparator<objects> sortById = (a,b) => a.result.compareTo(b.result);
items.sort(sortById);
filteritems = [
for (objects item in items) mappings[item]
];
print(filteritems);
}
@override
void initState() {
super.initState();
items = [
objects(title: 'Gummibärchen',number1: 1,number2: 3,result: 0),objects(title: 'Schokolade',number1: 5,number2: 2,objects(title: 'Eis',number1: 4,number2: 6,objects(title: 'Nutella',number1: 2,number2: 0,];
filteritems = ['Gummibärchen','Schokolade','Eis','Nutella' ];
berechnung();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Mapping'),),body: ListView.builder(
itemCount: items.length,itemBuilder: (context,index) {
return Card(
child: Container(
height: MediaQuery.of(context).size.height / 20,width: MediaQuery.of(context).size.width,child: Column(
children: <Widget>[
Text(items[index].title),Text(items[index].result.toString()),],);
},);
}
}
class objects {
String title;
int number1;
int number2;
int result;
objects({this.title,this.number1,this.number2,this.result});
}
我对编码非常陌生,所以我不理解自己编写的所有代码都很好,我只是复制了代码并希望做到最好,但这对我没有帮助。
我的行print(filteritems);
的输出为[null,null,null,null],我希望得到:
[Nutella,Gummibärchen,Schokolade,Eis],因为这是对其他列表进行排序的方式。
我希望有人能提供帮助,我将非常感谢。
解决方法
您可以在下面复制粘贴运行完整代码
您需要使用mappings[item.title]
而不是mappings[item]
filteritems = [for (objects item in items) mappings[item.title]];
输出
I/flutter (20843): [Nutella,Gummibärchen,Schokolade,Eis]
完整代码
import 'package:flutter/material.dart';
void main() => runApp(MaterialApp(home: App()));
List<objects> items = List<objects>();
List<String> filteritems = List();
class App extends StatefulWidget {
@override
_AppState createState() => _AppState();
}
class _AppState extends State<App> {
void berechnung() {
for (var i = 0; i < items.length; i++) {
items[i].result = items[i].number1 + items[i].number2;
}
print(items.toString());
final Map<String,String> mappings = {
for (int i = 0; i < items.length; i++) items[i].title: filteritems[i]
};
print(mappings.toString());
Comparator<objects> sortById = (a,b) => a.result.compareTo(b.result);
items.sort(sortById);
print(items.toString());
filteritems = [for (objects item in items) mappings[item.title]];
print(filteritems);
}
@override
void initState() {
super.initState();
items = [
objects(title: 'Gummibärchen',number1: 1,number2: 3,result: 0),objects(title: 'Schokolade',number1: 5,number2: 2,objects(title: 'Eis',number1: 4,number2: 6,objects(title: 'Nutella',number1: 2,number2: 0,];
filteritems = ['Gummibärchen','Schokolade','Eis','Nutella'];
berechnung();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Mapping'),),body: ListView.builder(
itemCount: items.length,itemBuilder: (context,index) {
return Card(
child: Container(
height: MediaQuery.of(context).size.height / 20,width: MediaQuery.of(context).size.width,child: Column(
children: <Widget>[
Text(items[index].title),Text(items[index].result.toString()),],);
},);
}
}
class objects {
String title;
int number1;
int number2;
int result;
objects({this.title,this.number1,this.number2,this.result});
}
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