Flutter 未处理的异常：Null 检查运算符用于 null 值

Question

我收到以下错误 Unhandled Exception: Null check operator 我不确定我的代码或我正在使用的库是否有问题。 我正在尝试测试 back4app 使用的 parse_server_sdk 的实时查询，因为我需要实时发送和接收图像。 这是相关代码：

 import 'dart:io';
import 'package:filepicker_windows/filepicker_windows.dart';
import 'package:flutter/material.dart';
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';

    void main() async {
      final keyApplicationId = 'EPARW6nRAAyp5uehoDE7rBEby4wtehcZf9EayykS';
      final keyClientKey = 'fDaL2DjyC9YdwCwZ4RB5c5vhACROaMOO1EjjL4Zn';
      final keyParseServerUrl = 'https://parseapi.back4app.com';
      final LIVE_QUERY_URL = 'wss://samuraichat.b4a.io';
    
      await Parse().initialize(keyApplicationId, keyParseServerUrl,
          clientKey: keyClientKey,
          autoSendSessionId: true,
          liveQueryUrl: LIVE_QUERY_URL,
          coreStore: CoreStoreMemoryImp());
    
      final LiveQuery liveQuery = LiveQuery();
    
      QueryBuilder<ParseObject> query =
          QueryBuilder<ParseObject>(ParseObject('FirstClass'))
            ..whereEqualTo('chatId', 1);
    
      Subscription subscription = await liveQuery.client.subscribe(query);
    
      subscription.on(LiveQueryEvent.create, (value) {
        print('*** CREATE ***: ${DateTime.now().toString()}\n $value ');
        print((value as ParseObject).objectId);
        print((value as ParseObject).get('message'));
      });
    
      runApp(MyApp());
    }

这是错误堆栈：

 [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: Null check operator used on a null value #0 MethodChannel.binaryMessenger (package:flutter/src/services/platform_channel.dart:142:86) #1 MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:148:36) #2 MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:331:12) #3 MethodChannelConnectivity.checkConnectivity (package:connectivity_platform_interface/src/method_channel_connectivity.dart:41:29) #4 Connectivity.checkConnectivity (package:connectivity/connectivity.dart:46:22) #5 Parse.checkConnectivity (package:parse_server_sdk_flutter/parse_server_sdk.dart:106:34) #6 new LiveQueryReconnectingController (package:parse_server_sdk/src.network/parse_live_query.dart:45:28) #7 new LiveQueryClient._internal (package:parse_server_sdk/src.network/parse_live_query.dart:146:30) #8 LiveQueryClient._getInstance (package:parse_server_sdk/src.network/parse_live_query.dart:153:35) #9 new LiveQuery (package:parse_server_sdk/src.network/parse_live_query.dart:416:30) #10 main (package:chat_app/main.dart:18:37) <asynchronous suspension>

谢谢。

Answer 1

尝试清理您的应用缓存：

flutter clean

Answer 2

这个错误应该用 这个 PR修复。

您可以通过覆盖 pubspec.yaml 中的依赖项来使用当前的pubspec.yaml分支：

dependency_overrides:
  parse_server_sdk_flutter:
    git:
      url: https://github.com/parse-community/Parse-SDK-Flutter.git
      ref: nullsafety
      path: packages/flutter
  parse_server_sdk:
    git:
      url: https://github.com/parse-community/Parse-SDK-Flutter.git
      ref: nullsafety
      path: packages/dart