flutter赋值的时候报错，但是数据已经获取到了

Question

问题描述：
movieDetails是电影详情获取到的数据对象，在给
images = movieDetails['images'];
large = images['large'];
赋值的时候回出现以上错误，打印输出的时候，值是正确的，只是页面显示的时候会先出现错误页面然后恢复正常。

import 'package:flutter/material.dart';
//加载请求工具
import 'package:dio/dio.dart';

Dio dio = new Dio();

//电影详情页
class MovieDetail extends StatefulWidget {
MovieDetail({Key key, @required this.id, @required this.title})

  : super(key: key);

final String id;
final String title;
_MovieDetailState createState() => _MovieDetailState();
}
class _MovieDetailState extends State<MovieDetail> {
//电影详情
var movieDetails = {};
@override
void initState() {

super.initState();
//获取电影详情
getMovieDetail();

}
//获取电影详情
getMovieDetail() async {

//获取电影详情
print(widget.id);
var response =
    await dio.get('http://api.douban.com/v2/movie/subject/${widget.id}');
var result = response.data;
// 设置获取的值
if (result != null) {
  setState(() {
    movieDetails = result;
  });
}

}

@override
Widget build(BuildContext context) {

// print('movie------${movieDetail}');
var detail = movieDetails;
var summary="";
var images={};
var large="";
summary = movieDetails['summary'];
images = movieDetails['images'];
// images = ;

// print(images);

large = images['large'];
print(large);
var info = movieDetails['year']+'/'+movieDetails['countries'].join('/')+'/'+movieDetails['genres'].join('/');
return Scaffold(
    appBar: AppBar(
      title: Text(widget.title),
      centerTitle: true,
    ),
    body: Container(
      child: Column(
        children: <Widget>[
          Container(
            padding: EdgeInsets.only(top: 50, bottom: 30),
            color: Color.fromRGBO(23, 45, 74,1),
            child: Align(
              child: Image.network(
               movieDetails['images']['large'].toString(),
                width: 200.0,
              ),
              alignment: Alignment.center,
            ),
          ),
          Container(
            child: Column(
              children: <Widget>[
                Padding(
                  padding: EdgeInsets.only(left: 20, top: 20),
                ),
                Container(
                  padding: EdgeInsets.only(left: 20),
                  child: Row(
                    children: <Widget>[
                      Expanded(
                        child: Column(
                          crossAxisAlignment: CrossAxisAlignment.start,
                          mainAxisAlignment: MainAxisAlignment.start,
                          children: <Widget>[
                            Text(
                              '${widget.title}',
                              softWrap: true,
                              style: TextStyle(
                                  fontSize: 22,
                                  fontWeight: FontWeight.bold),
                            ),
                            Text(
                              info,
                              softWrap: true,
                              style: TextStyle(fontSize: 12),
                            ),
                          ],
                        ),
                      ),
                    ],
                  ),
                )
              ],
            ),
          ),
          Container(
            padding: EdgeInsets.only(left: 20,top: 20),
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              mainAxisAlignment: MainAxisAlignment.spaceAround,
              children: <Widget>[
                Container(
                  child:Text('剧情简介',
                    softWrap: true,
                    ),
                ),
                Container(
                  padding: EdgeInsets.only(right: 20,top: 10),
                  child: 
                    Text(
                      summary,
                      maxLines: 40,
                      softWrap: true,
                    ),
                  
                )
              ],
            ),
          ),
        ],
      ),
    )
);

}
}

问题出现的环境背景及自己尝试过哪些方法

相关代码

// 请把代码文本粘贴到下方（请勿用图片代替代码）

你期待的结果是什么？实际看到的错误信息又是什么？

Answer 1

请求是异步的，在数据获取到之前，movieDetails['images']都是空，当然会报错，做好空值判断吧

Answer 2

判断null时显示一个加载提示 Center(child: CircularProgressIndicator(),) 等异步加载后在显示正常页面