Question

我正在尝试制作流畅的Web应用程序。但是问题出在哪里，无论何时我刷新页面或第一次出现错误时出现在屏幕上，然后过一会儿检索值就出现在屏幕上并且错误消失了。

以下：

在构建StreamBuilder时引发NoSuchMethodError（脏，状态： _StreamBuilderBaseState>＃6203e）：
'文档'
找不到方法
接收者：null
参数：[]

我想知道为什么这种行为在页面上发生？问题出在哪里？

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:fulltext_search/study.dart';
import 'package:fulltext_search/study_search.dart';
import 'package:fulltext_search/visitor.dart';


void main() {
  runApp(StudentSearchData());
}

class StudentSearchData extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  var queryResultSet = [];
  var tempSearchStore = [];

  initiateSearch(value) {
    if (value.length == 0) {
      setState(() {
        queryResultSet = [];
        tempSearchStore = [];
      });
    }

    var capitalizedValue = value.substring(0, 1).toUpperCase() + value.substring(1);
    var lowerValue = value.substring(0, 1).toLowerCase() + value.substring(1);

    if (queryResultSet.length == 0 && value.length == 1) {
      SearchService().searchByName(value).then((QuerySnapshot docs) {
        for (int i = 0; i < docs.documents.length; ++i) {
          queryResultSet.add(docs.documents[i].data);
        }
      });
    } else {
      tempSearchStore = [];
      queryResultSet.forEach((element) {
        if (element['fname'].startsWith(capitalizedValue)) {
          setState(() {
            tempSearchStore.add(element);
          });
        }
        if (element['fname'].startsWith(lowerValue)) {
          setState(() {
            tempSearchStore.add(element);
          });
        }
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    var size = MediaQuery.of(context).size;

    /*24 is for notification bar on Android*/
    final double itemHeight = (size.height - kToolbarHeight-24)/3;
    final double itemWidth = size.width / 2;
    return new Scaffold(
        appBar: new AppBar(
          title: Text('Student data search'),
          actions: <Widget>[

            FlatButton(
              textColor: Colors.white,
              onPressed: () {
                Navigator.push(context, MaterialPageRoute(builder: (context) => Student()),);
              },
              child: Text("Student",),
            ),

            FlatButton(
              textColor: Colors.white,
              onPressed: () {
                Navigator.push(context, MaterialPageRoute(builder: (context) => Visitor()),);
              },
              child: Text("Visitor",),
            ),
            FlatButton(
              color: Colors.grey[400],
              shape: RoundedRectangleBorder(
                side: BorderSide(color: Colors.white,width: 1),
                borderRadius: BorderRadius.circular(10),
              ),
              textColor: Colors.black87,
              onPressed: () {},
              child: Text("History",style: TextStyle(fontSize: 15,fontWeight: FontWeight.bold),),

            ),
            FlatButton(

              textColor: Colors.white,
              onPressed: () {
                //Navigator.push(context, MaterialPageRoute(builder: (context) => VisitorHistory()),);
              },
              child: Text("Logout",),
            ),

          ],
        ),
        body: ListView(children: <Widget>[
          Padding(
            padding: const EdgeInsets.all(10.0),
            child: TextField(
              onChanged: (val) {
                initiateSearch(val);
              },
              decoration: InputDecoration(
                  prefixIcon: IconButton(
                    color: Colors.black,
                    icon: Icon(Icons.arrow_back),
                    iconSize: 20.0,
                    onPressed: () {
                      Navigator.of(context).pop();
                    },
                  ),
                  contentPadding: EdgeInsets.only(left: 25.0),
                  hintText: 'Search by name',
                  border: OutlineInputBorder(
                      borderRadius: BorderRadius.circular(4.0))),
            ),
          ),
          SizedBox(height: 10.0),
          GridView.count(
              childAspectRatio: (itemWidth / itemHeight),
              padding: EdgeInsets.only(left: 10.0, right: 10.0),
              crossAxisCount: 2,
              //scrollDirection: Axis.horizontal,
              crossAxisSpacing: 4.0,
              mainAxisSpacing: 4.0,
              primary: false,
              shrinkWrap: true,
              children: tempSearchStore.map((element) {
                return buildResultCard(element);
              }).toList())
        ]));
  }
}

Widget buildResultCard(data) {
    return Scaffold(
      body: SingleChildScrollView(
        child: Container(
          child: Card(
            color: Colors.white,
            shape: RoundedRectangleBorder(
              side: BorderSide(color: Colors.blue,width: 2),
              borderRadius: BorderRadius.circular(10),
            ),
            child: Padding(
              padding: const EdgeInsets.all(16.0),

              child: Row(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: <Widget>[
                  Container(
                width:120,
                    child: Row(children: <Widget>[
                      Image.network(data['image'], width:120,height: 120,fit: BoxFit.cover,),
                      Spacer(),
                    ]),
                  ),

                  SizedBox(width: 10),

                  Expanded(
                    child: Column(
                      crossAxisAlignment: CrossAxisAlignment.start,
                      children: <Widget>[
                        Text('Name:- ${data['fname']}\n', style: new TextStyle(fontSize: 12.0,color: Colors.black),),
                        Text('Year:- ${data['year']}\n', style: new TextStyle(fontSize: 12.0,color: Colors.black),),
                        Text('Contact no:- ${data['contact']}\n', style: new TextStyle(fontSize: 12.0,color: Colors.black),),
                        Text('Vehicle no:- ${data['vehicleno']}\n', style: new TextStyle(fontSize: 12.0,color: Colors.black),),
                        Row(
                          children: <Widget>[
                            Expanded(
                              child: Text('purpose of visiting:- ${data['purpose']}\n', style: new TextStyle(fontSize: 12.0,),),
                            ),

                          ],
                        ),
                        Text('Entry-time:- ${data['Entry-time']}\n', style: new TextStyle(fontSize: 12.0,),),
                        Text('Exit-time:- ${data['Exit-time']}\n', style: new TextStyle(fontSize: 12.0,),),
                      ],
                    ),
                  )

                ],
              ),
            ),
          ),
        ),
      ),
    );
  }

enter image description here

Answer 1

如果数据不为null，则添加if else语句以返回小部件，如果为null，则返回加载ui。

Answer 2

错误似乎来自以下代码段：

Data:

您对SearchService().searchByName(value).then((QuerySnapshot docs) { for (int i = 0; i < docs.documents.length; ++i) { queryResultSet.add(docs.documents[i].data); } });的调用似乎可以通过searchByName(value)的{{1}}来解决，然后导致docs抛出错误。

无法说出null返回docs.documents的原因而没有看到代码。

Answer 3

尝试首先使用 (snapshot.hasData) 检查快照数据，如果快照为空则返回 Circular Progress Indicator。这将解决这个问题。

Answer 4

发生这种情况是因为最初快照没有任何数据。可以通过一定的条件检查数据是否已经到达快照。

if(snapshot.hasData){
  return MainWidget();
}else if(snapshot.hasData){
  return Text("Error in loading data”);
}else{
  return SizedBox(
    height: 30,
    width: 30,
    child: CircularProgressIndicator(
    ),
  );
}

为什么先显示红色错误屏幕，然后在屏幕上显示获取的值？问题出在哪儿

4 个答案: