android - NoSuchMethodError，迭代器调用为null

Question

I/flutter ( 8282): The following NoSuchMethodError was thrown building Meme(dirty, state: _MemeState#77e49):
I/flutter ( 8282): The getter 'iterator' was called on null.
I/flutter ( 8282): Receiver: null
I/flutter ( 8282): Tried calling: iterator
I/flutter ( 8282): 
I/flutter ( 8282): The relevant error-causing widget was:
I/flutter ( 8282):   Meme file:///F:/android_studio_projects/daily_indian_memes/lib/main.dart:7:9
I/flutter ( 8282): 
I/flutter ( 8282): When the exception was thrown, this was the stack:
I/flutter ( 8282): #0      Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5)
I/flutter ( 8282): #1      _MemeState.build (package:dailyindianmemes/main.dart:102:30)
I/flutter ( 8282): #2      StatefulElement.build (package:flutter/src/widgets/framework.dart:4334:27)
I/flutter ( 8282): #3      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4223:15)
I/flutter ( 8282): #4      Element.rebuild (package:flutter/src/widgets/framework.dart:3947:5)
I/flutter ( 8282): #5      ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4206:5)
I/flutter ( 8282): #6      StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4381:11)
I/flutter ( 8282): #7      ComponentElement.mount (package:flutter/src/widgets/framework.dart:4201:5)
I/flutter ( 8282): #8      Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14)
I/flutter ( 8282): #9      Element.updateChild (package:flutter/src/widgets/framework.dart:2988:12)
I/flutter ( 8282): #10     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5445:14)
I/flutter ( 8282): #11     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14)
I/flutter ( 8282): #12     Element.updateChild (package:flutter/src/widgets/framework.dart:2988:12)
I/flutter ( 8282): #13     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4243:16)
I/flutter ( 8282): #14     Element.rebuild (package:flutter/src/widgets/framework.dart:3947:5)
I/flutter ( 8282): #15     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4206:5)
I/flutter ( 8282): #16     ComponentElement.mount (package:flutter/src/widgets/framework.dart:4201:5)
I/flutter ( 8282): #17     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14)
I/flutter ( 8282): #18     Element.updateChild (package:flutter/src/widgets/framework.dart:2988:12)
I/flutter ( 8282): #19     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5445:14)
I/flutter ( 8282): #20     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14)
I/flutter ( 8282): #21     Element.updateChild (package:flutter/src/widgets/framework.dart:2988:12)
I/flutter ( 8282): #22     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5445:14)
I/flutter ( 8282): #23     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14)
I/flutter ( 8282): #24     Element.updateChild (package:flutter/src/widgets/framework.dart:2988:12)
I/flutter ( 8282): #25     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4243:16)
I/flutter ( 8282): #26     Element.rebuild (package:flutter/src/widgets/framework.dart:3947:5)
I/flutter ( 8282): #27     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4206:5)
I/flutter ( 8282): #28     StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4381:11)
I/flutter ( 8282): #29     ComponentElement.mount (package:flutter/src/widgets/framework.dart:4201:5)
I/flutter ( 8282): #30     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14)
I/flutter ( 8282): #31     Element.updateChild (package:flutter/src/widgets/framework.dart:2988:12)
I/flutter ( 8282): #32     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5445:14)
I/flutter ( 8282): #33     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14)
I/flutter ( 8282): #34     Element.updateChild (package:flutter/src/widgets/framework.dart:2988:12)
I/flutter ( 8282): #35     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5445:14)
I/flutter ( 8282): #36     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14)
I/flutter ( 8282): #37     Element.updateChild (package:flutter/src/widgets/framework.dart:2988:12)
I/flutter ( 8282): #38     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4243:16)
I/flutter ( 8282): #39     Element.rebuild (package:flutter/src/widgets/framework.dart:3947:5)
I/flutter ( 8282): #40     ComponentElement._firstBuild 

这是代码:

import 'package:flutter/material.dart';
import 'package:dailyindianmemes/about.dart';
import 'package:http/http.dart';

void main() => runApp(MaterialApp(
    home: Meme(),
));

class Meme extends StatefulWidget {
    @override
    _MemeState createState() => _MemeState();
}

class _MemeState extends State<Meme> {
    var len ;

    void getData() async {
        Response response = await get('http://glappy.freeasphost.net/');
        var urlBunch = response.body;

        List<String> urls = new List();
        urls = urlBunch.split(',');
    }

    @override
    void initState() {
        super.initState();
        getData();
    }

    Widget build(BuildContext context) {
        return Scaffold(
            backgroundColor: Colors.grey[850],
            appBar: AppBar(
                centerTitle: true,
                backgroundColor: Colors.grey[850],
                title: Text(
                    'Indian Memes',
                    style: TextStyle(
                        color: Colors.white,
                        letterSpacing: 1,
                        fontSize: 25,
                        fontWeight: FontWeight.bold
                    ),
                ),
            ),
            drawer: Drawer(
                child: Container(
                    color: Colors.grey[850],
                    child: ListView(
                        padding: EdgeInsets.zero,
                        children: <Widget>[
                            DrawerHeader(
                                padding: EdgeInsets.zero,
                                child: Text(
                                    '       Indian Memes ',
                                    style: TextStyle(
                                    color: Colors.white,
                                    letterSpacing: 1.5,
                                    fontSize: 25,
                                    fontWeight: FontWeight.bold,
                               ),
                           ),
                           decoration: BoxDecoration(
                               color: Colors.grey[850],
                           ),
                       ),
                       ListTile(
                           leading: Icon(Icons.image,color: Colors.grey),
                           title: Text('Memes',
                               style: TextStyle(
                                   color: Colors.white
                               ),
                           ), 
                           onTap: (){
                               //to the page navigating to...
                               Navigator.pop(context);
                           },
                       ),
                       ListTile(
                           leading: Icon(Icons.info_outline,color: Colors.grey,),
                           title: Text('About',
                               style: TextStyle(color: Colors.white)),
                               onTap: (){
                                   Navigator.push(context, MaterialPageRoute(builder: (context) => About()));
                               },
                       ),
                       for ( var i in len ) Text(i.toString())
                   ],
              ),
          ),
      ),
      body: ListView(
          padding: EdgeInsets.fromLTRB(0, 0, 0, 10),
          children: <Widget>[
          ],
      )
  );
}
}

我怎样才能解决这个问题？

Answer 1

错误的关键部分是:

The getter 'iterator' was called on null

这意味着您试图遍历null的值的集合(如列表)。因此，我猜urls = urlBunch.split(',');是问题所在。尝试检查列表中是否首先包含诸如此类的值

 if(urls != null){
urls = urlBunch.split(',');
    }