I am trying to develop a flutter app. This flutter is creating teams for a card game. After the creation of the team, the points could be counted through the, so that you don't have to think about how many points everybody has.

But I got an exception, where I know where the exception and what it means, but i do not have any clue how i could solve the problem. I hope some of you guys could help me.

This is the code where the error is thrown:

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"); } }
}

And this is the error message:

══╡ 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

After the fix, I got another error:

══╡ 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.

1

6 Answers

punkteanzahl_teamEins is only declared. But not initialized. So it is throwing null error.

You should assign value to punkteanzahl_teamEins as

List<int> punkteanzahl_teamEins = [1,4,5,7];

or pass data from parent as requirement.

4

We spend lost's of time to resolve issue finally we got a solution is: Please check you pubspec.yaml and remove extra '-' in case of assets file and also please follow the structure of that like spacing and all that.

We are must sure that issue only in pubspec.yaml file

0

First one check spieler_namen is null or not.If it is null then use below code i hope this will solve your problem.....

if(spieler_namen == null){ new Container(width: 10.0,height: 10.0,); }else{ your requirement ....... }

In our case, we got this error when Internet Connection is off after calling webservice.

1

Initialize your list, and run hot restart (press R).

It works correctly.

I fix this by revisiting this section in pubspec.yaml

# To add assets to your application, add an assets section, like this:
# assets:
# - images/a_dot_burr.jpeg
# - images/a_dot_ham.jpeg

Ensure your spacing, hyphens and filenames are correct. Note: You do not need to list every image file; instead, you can just list their directory:

assets:
- images/

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