我正在尝试开发一个Flutter应用程序。这种动荡正在为纸牌游戏创建团队。团队创建后,积分可以计入,因此您不必考虑每个人有多少积分。
但是我有一个例外,我知道例外在哪里及其含义,但是我不知道如何解决该问题。我希望你们中的一些人能帮助我。
这是引发错误的代码:
import 'package:flutter/material.dart';
class Punktezaehler extends StatefulWidget{
final List<String> spieler_namen;
Punktezaehler(this.spieler_namen);
@override
State<StatefulWidget> createState() => new _Punktezaehler(this.spieler_namen);
}
class _Punktezaehler extends State<Punktezaehler>{
final List<String> spieler_namen;
_Punktezaehler(this.spieler_namen);
List<int> punkteanzahl_teamEins;
List<int> punkteanzahl_teamZwei;
@override
Widget build(BuildContext context) {
var spieler1 = spieler_namen[0].substring(0,3);
var spieler2 = spieler_namen[1].substring(0,3);
var spieler3 = spieler_namen[2].substring(0,3);
var spieler4 = spieler_namen[3].substring(0,3);
return new Scaffold(
appBar: new AppBar(
automaticallyImplyLeading: false,
title: new Text("$spieler1 & $spieler2 vs" +" $spieler3 & $spieler4"),
actions: <Widget>[
],
),
body: Container(
child: new Row(
children: <Widget>[
new Column(
children: <Widget>[
new IconButton(
icon: Icon(Icons.exposure_plus_2),
onPressed: () => punkte_hinzuzaehlen(1, 2)
)
],
),
new Column(
children: <Widget>[
//new FlatButton(onPressed: () => print(punkteanzahl_teamEins.length), child: new Text("Punkte")),
ListView.builder(
itemCount: punkteanzahl_teamEins.length, //--> Error is thrown here
itemBuilder: (context, index){
return Text(punkteanzahl_teamEins[index].toString());
}
),
new Row()
],
),
new Column(
children: <Widget>[
new IconButton(
icon: Icon(Icons.exposure_plus_2),
onPressed: () => punkte_hinzuzaehlen(2, 2)
)],
)
],
)
),
);
}
void punkte_hinzuzaehlen(int team, int nummer){
if (team == 1){
//Team 1 bekommt die Punkte
print("Team 1 gets points");
}
else if(team == 2){
//Team 2 bekommt die Punkte
print("Team 2 gets points");
}
}
}
这是错误消息:
══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
I/flutter (26028): The following NoSuchMethodError was thrown while handling a gesture:
I/flutter (26028): The getter 'length' was called on null.
I/flutter (26028): Receiver: null
I/flutter (26028): Tried calling: length
修复后,我得到另一个错误:
══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
I/flutter (26028): The following assertion was thrown during performResize():
I/flutter (26028): Vertical viewport was given unbounded width.
I/flutter (26028): Viewports expand in the cross axis to fill their container and constrain their children to match
I/flutter (26028): their extent in the cross axis. In this case, a vertical viewport was given an unlimited amount of
I/flutter (26028): horizontal space in which to expand.
仅声明punkteanzahl_teamEins。但未初始化。因此,它引发空错误。
您应该将值分配punkteanzahl_teamEins
为
List<int> punkteanzahl_teamEins = [1,4,5,7];
或根据需要传递来自父级的数据。
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我来说两句