错误“在 null 上调用了方法 '[]'。接收方：null 尝试调用：[]("0tm2JqPY0oNq5vSM74BqOufhGao1")”
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【中文标题】错误“在 null 上调用了方法 \'[]\'。接收方：null 尝试调用：[]("0tm2JqPY0oNq5vSM74BqOufhGao1")”【英文标题】：Error "The method '[]' was called on null. Receiver: null Tried calling: []("0tm2JqPY0oNq5vSM74BqOufhGao1")"错误“在 null 上调用了方法 '[]'。接收方：null 尝试调用：[]("0tm2JqPY0oNq5vSM74BqOufhGao1")” 【发布时间】：2021-06-01 00:01:09 【问题描述】：添加投票功能后，我在投票帖子页面中收到此错误：
我添加的新方法是 handleTotalVotePosts 来处理 userPostPolls 的计数（在第 178 行）。 我认为错误是获取 userId 或我不确定的东西。
我不确定这里到底出了什么问题
The method '[]' was called on null. Receiver: null Tried calling: []("0tm2JqPY0oNq5vSM74BqOufhGao1")
但代码似乎是正确的
This my **pollPost.dart**
import 'package:cached_network_image/cached_network_image.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:justpoll/libmodels/user_model.dart';
import 'package:justpoll/screens/chat/chat_data.dart';
import 'package:justpoll/widgets/progress.dart';
import 'package:justpoll/widgets/toast_text.dart';
import '../Constants.dart';
import 'package:justpoll/widgets/custom_image.dart';
import 'package:animated_button/animated_button.dart';
class PollPost extends StatefulWidget
final String pollPostId;
final String mediaUrl;
final String ownerId;
final String username;
final String caption;
final String category;
final String colorTheme;
final Timestamp duration;
final String question;
final dynamic votesTotal;
final String optText1;
final String optText2;
final String optText3;
final String optText4;
final String optemo1;
final String optemo2;
final String optemo3;
final String optemo4;
final String optCount1;
final String optCount2;
final String optCount3;
final String optCount4;
PollPost(
this.pollPostId,
this.mediaUrl,
this.ownerId,
this.username,
this.caption,
this.category,
this.colorTheme,
this.duration,
this.question,
this.votesTotal,
this.optText1,
this.optText2,
this.optText3,
this.optText4,
this.optemo1,
this.optemo2,
this.optemo3,
this.optemo4,
this.optCount1,
this.optCount2,
this.optCount3,
this.optCount4,
);
factory PollPost.fromDocument(DocumentSnapshot doc)
return PollPost(
pollPostId: doc['pollPostid'],
mediaUrl: doc['mediaUrl'],
ownerId: doc['ownerId'],
username: doc['username'],
caption: doc['caption'],
category: doc['category'],
colorTheme: doc['colorTheme'],
duration: doc['Duration'],
question: doc['Question'],
votesTotal: doc['votesTotal'],
optText1: doc["options"]["1"]["optionText1"],
optText2: doc["options"]["2"]["optionText2"],
optText3: doc["options"]["3"]["optionText3"],
optText4: doc["options"]["4"]["optionText4"],
optemo1: doc["options"]["1"]["optionEmoji1"],
optemo2: doc["options"]["2"]["optionEmoji2"],
optemo3: doc["options"]["3"]["optionEmoji3"],
optemo4: doc["options"]["4"]["optionEmoji4"],
// optCount1: doc["options"]["1"]["optionCount1"],
// optCount2: doc["options"]["2"]["optionCount2"],
// optCount3: doc["options"]["3"]["optionCount3"],
// optCount4: doc["options"]["4"]["optionCount4"],
);
int getreactionsTotalCount(votesTotal)
if (votesTotal == null)
return 0;
int count = 0;
votesTotal.values.forEach((val)
if (val = true)
count += 1;
);
return count;
@override
_PollPostState createState() => _PollPostState(
pollPostId: this.pollPostId,
mediaUrl: this.mediaUrl,
ownerId: this.ownerId,
username: this.username,
caption: this.caption,
category: this.category,
colorTheme: this.colorTheme,
duration: this.duration,
question: this.question,
optText1: this.optText1,
optText2: this.optText2,
optText3: this.optText3,
optText4: this.optText4,
optemo1: this.optemo1,
optemo2: this.optemo2,
optemo3: this.optemo3,
optemo4: this.optemo4,
votesTotalCount: getreactionsTotalCount(this.votesTotal),
);
class _PollPostState extends State<PollPost>
GlobalKey floatingKey = LabeledGlobalKey("Floating");
bool isFloatingOpen = false;
OverlayEntry floating;
static FirebaseAuth auth = FirebaseAuth.instance;
final userRef = FirebaseFirestore.instance.collection("users");
final pollPostsRef = FirebaseFirestore.instance.collection("pollPosts");
final String currentUserId = auth.currentUser?.uid;
final String pollPostId;
final String mediaUrl;
final String ownerId;
final String username;
final String caption;
final String category;
final String colorTheme;
final Timestamp duration;
final String question;
final String optText1;
final String optText2;
final String optText3;
final String optText4;
final String optemo1;
final String optemo2;
final String optemo3;
final String optemo4;
int votesTotalCount;
Map votesTotal;
bool isVoted;
_PollPostState(
this.pollPostId,
this.mediaUrl,
this.ownerId,
this.username,
this.caption,
this.category,
this.colorTheme,
this.duration,
this.question,
this.votesTotal,
this.votesTotalCount,
this.optText1,
this.optText2,
this.optText3,
this.optText4,
this.optemo1,
this.optemo2,
this.optemo3,
this.optemo4,
);
handleTotalVotePosts()
bool _isVoted = votesTotal[currentUserId] == true;
if (_isVoted)
pollPostsRef
.doc(ownerId)
.collection('usersPollPosts')
.doc(pollPostId)
.update('votesTotal.$currentUserId': false);
setState(()
votesTotalCount -= 1;
isVoted = false;
votesTotal[currentUserId] = false;
);
else if (!_isVoted)
pollPostsRef
.doc(ownerId)
.collection('usersPollPosts')
.doc(pollPostId)
.update('votesTotal.$currentUserId': true);
setState(()
votesTotalCount += 1;
isVoted = true;
votesTotal[currentUserId] = true;
);
OverlayEntry createFloating()
RenderBox renderBox = floatingKey.currentContext.findRenderObject();
Offset offset = renderBox.localToGlobal(Offset.zero);
return OverlayEntry(builder: (context)
return Positioned(
left: offset.dx,
top: offset.dy - 70,
child: Material(
color: Colors.transparent,
elevation: 20,
child: ClipRRect(
borderRadius: BorderRadius.circular(40.0),
child: Container(
padding: EdgeInsets.all(5.0),
height: 50,
color: MyColors.black,
child: Row(
children: [
Padding(
padding: const EdgeInsets.all(5.0),
child: AnimatedButton(
onPressed: ()
handleTotalVotePosts();
toastMessage("You voted for $optText1 $optemo1");
setState(()
if (isFloatingOpen)
floating.remove();
else
floating = createFloating();
Overlay.of(context).insert(floating);
isFloatingOpen = !isFloatingOpen;
);
,
duration: 20,
enabled: true,
width: 30,
height: 30,
color: MyColors.black,
shadowDegree: ShadowDegree.light,
child:
Text(optemo1, style: TextStyle(fontSize: 20.0)))),
Padding(
padding: const EdgeInsets.all(5.0),
child: AnimatedButton(
onPressed: ()
toastMessage("You voted for $optText2 $optemo2");
setState(()
handleTotalVotePosts();
if (isFloatingOpen)
floating.remove();
else
floating = createFloating();
Overlay.of(context).insert(floating);
isFloatingOpen = !isFloatingOpen;
);
,
duration: 20,
enabled: true,
width: 30,
height: 30,
color: MyColors.black,
shadowDegree: ShadowDegree.light,
child:
Text(optemo2, style: TextStyle(fontSize: 20.0)))),
optText3.isEmpty
? Text("")
: Padding(
padding: const EdgeInsets.all(5.0),
child: AnimatedButton(
onPressed: ()
handleTotalVotePosts();
toastMessage(
"You voted for $optText3 $optemo3");
setState(()
if (isFloatingOpen)
floating.remove();
else
floating = createFloating();
Overlay.of(context).insert(floating);
isFloatingOpen = !isFloatingOpen;
);
,
duration: 20,
enabled: true,
width: 30,
height: 30,
color: MyColors.black,
shadowDegree: ShadowDegree.light,
child: Text(optemo3,
style: TextStyle(fontSize: 20.0)))),
optText4.isEmpty
? Text("")
: Padding(
padding: const EdgeInsets.all(5.0),
child: AnimatedButton(
onPressed: ()
handleTotalVotePosts();
toastMessage(
"You voted for $optText4 $optemo4");
setState(()
if (isFloatingOpen)
floating.remove();
else
floating = createFloating();
Overlay.of(context).insert(floating);
isFloatingOpen = !isFloatingOpen;
);
,
duration: 20,
enabled: true,
width: 30,
height: 30,
color: MyColors.black,
shadowDegree: ShadowDegree.light,
child: Text(optemo4,
style: TextStyle(fontSize: 20.0)))),
],
),
),
),
),
);
);
buildPollPostHeader()
return FutureBuilder(
future: userRef.doc(ownerId).get(),
builder: (context, snapshot)
if (!snapshot.hasData)
return circularProgress();
UserModel user = UserModel.fromMap(snapshot.data.data());
return ListTile(
leading: CircleAvatar(
backgroundImage: CachedNetworkImageProvider(user.photoUrl),
backgroundColor: Colors.grey,
),
title: GestureDetector(
onTap: () => toastMessage("showing profile"),
child: Text(
user.username,
style: TextStyle(
color: MyColors.black,
fontWeight: FontWeight.bold,
),
),
),
subtitle: Text(category),
trailing: IconButton(
onPressed: () => toastMessage("pop up menu"),
icon: Icon(Icons.more_vert),
),
);
,
);
buildPollPostCenter()
return Column(
children: [
Padding(
padding: const EdgeInsets.all(8.0),
child: Text(
question,
style: TextType.boldHeading,
),
),
mediaUrl == null
? Center(
child: Container(
height: 30.0,
))
: ClipRRect(
borderRadius: BorderRadius.circular(10),
child: chachedNetworkImage(
mediaUrl,
),
),
Padding(
padding: const EdgeInsets.symmetric(vertical: 10.0),
child: Column(
children: [
Column(
children: [
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text(
optText1,
style: TextStyle(
color: MyColors.offBlack,
fontSize: 16.0,
),
),
Text(optemo1),
SizedBox(
width: 25.0,
),
Text(
optText2,
style: TextStyle(
color: MyColors.offBlack,
fontSize: 16.0,
),
),
Text(optemo2),
],
),
],
),
SizedBox(height: 13.0),
Column(
children: [
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text(
optText3,
style: TextStyle(
color: MyColors.offBlack,
fontSize: 16.0,
),
),
Text(optemo3),
SizedBox(
width: 25.0,
),
Text(
optText4,
style: TextStyle(
color: MyColors.offBlack,
fontSize: 16.0,
),
),
Text(optemo4),
],
),
],
),
],
),
),
],
);
buildPollPostFooter()
return Column(
children: [
Align(
alignment: Alignment.bottomLeft,
child: Expanded(
child: Row(
mainAxisAlignment: MainAxisAlignment.start,
children: [
Padding(padding: EdgeInsets.only(top: 40.0, left: 20.0)),
isVoted
? GestureDetector(
key: floatingKey,
onTap: ()
setState(()
if (isFloatingOpen)
floating.remove();
else
floating = createFloating();
Overlay.of(context).insert(floating);
isFloatingOpen = !isFloatingOpen;
);
,
child: Icon(
Icons.poll,
color: MyColors.offBlack,
size: 28.0,
),
)
: Icon(Icons.check_circle),
Padding(padding: EdgeInsets.only(right: 20.0)),
GestureDetector(
onTap: () => toastMessage("show comments"),
child: Icon(
Icons.chat,
color: MyColors.offBlack,
size: 28.0,
),
),
Padding(padding: EdgeInsets.only(right: 20.0)),
GestureDetector(
onTap: () => toastMessage("saved successfully"),
child: Icon(
Icons.bookmark,
color: MyColors.offBlack,
size: 28.0,
),
),
Padding(padding: EdgeInsets.only(right: 20.0)),
Expanded(
child: Row(
mainAxisAlignment: MainAxisAlignment.end,
children: [
GestureDetector(
onTap: () => toastMessage("sharing with friends"),
child: Align(
alignment: Alignment.topRight,
child: Icon(
Icons.send,
color: MyColors.offBlack,
size: 28.0,
),
),
),
Padding(padding: EdgeInsets.only(right: 25.0)),
],
),
),
],
),
),
),
Row(
children: [
Container(
margin: EdgeInsets.only(left: 20.0, top: 5.0),
child: Text(
"$votesTotalCount votes",
style: TextStyle(
color: MyColors.black,
fontWeight: FontWeight.bold,
),
),
),
Container(
margin: EdgeInsets.only(left: 20.0, top: 5.0),
child: Text(
"expiring in 4 days",
style: TextStyle(
color: MyColors.black,
fontWeight: FontWeight.bold,
),
),
)
],
),
Padding(
padding: const EdgeInsets.only(top: 5.0, bottom: 10.0),
child: Row(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Container(
margin: EdgeInsets.only(left: 20.0),
child: Text(
"$username ",
style: TextStyle(
color: MyColors.black,
fontWeight: FontWeight.bold,
),
),
),
Expanded(
child: Text(caption),
),
],
),
)
],
);
@override
Widget build(BuildContext context)
isVoted = (votesTotal[currentUserId] == true);
return Card(
elevation: 1.0,
child: Column(
mainAxisSize: MainAxisSize.min,
children: [
buildPollPostHeader(),
buildPollPostCenter(),
buildPollPostFooter(),
],
),
);
请帮助我摆脱这个错误。 谢谢你:)
【问题讨论】：
你能指定哪个代码，因为我找不到第 178 行，谢谢。 关于 handleTotalVotePosts 方法 【参考方案1】：请在您的handleTotalVotePosts 方法中写入以下代码：
if(votesTotal == null)
return;
【讨论】：
以上是关于错误“在 null 上调用了方法 '[]'。接收方：null 尝试调用：[]("0tm2JqPY0oNq5vSM74BqOufhGao1")”的主要内容，如果未能解决你的问题，请参考以下文章
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