Dart项目使用Parse LiveQuery报错无ParseConnectivityProvider如何解决？

错误根因 #

你遇到的报错是因为parse_server_sdk包默认内置的连通性检测提供器仅适配Flutter环境，纯Dart运行环境没有默认实现，必须手动传入自定义的connectivityProvider参数完成初始化。

解决步骤 #

1. 自定义实现极简连通性提供器，纯Dart环境无需复杂的系统网络状态监听，直接固定返回网络连通状态即可：

class CustomParseConnectivityProvider extends ParseConnectivityProvider {
  @override
  Future<ParseConnectivityResult> checkConnectivity() async {
    return ParseConnectivityResult.connected;
  }

  @override
  Stream<ParseConnectivityResult> get connectivityStream =>
      Stream.value(ParseConnectivityResult.connected);
}

2. 修改Parse初始化逻辑，新增connectivityProvider参数传入上面的自定义实现：

await Parse().initialize(
  keyApplicationId,
  keyParseServerUrl,
  clientKey: keyClientKey,
  liveQueryUrl: liveQueryURL,
  autoSendSessionId: true,
  debug: true,
  // 新增这一行
  connectivityProvider: CustomParseConnectivityProvider(),
);

完整可运行代码 #

import 'package:parse_server_sdk/parse_server_sdk.dart';

// 自定义连通性提供器
class CustomParseConnectivityProvider extends ParseConnectivityProvider {
  @override
  Future<ParseConnectivityResult> checkConnectivity() async {
    return ParseConnectivityResult.connected;
  }

  @override
  Stream<ParseConnectivityResult> get connectivityStream =>
      Stream.value(ParseConnectivityResult.connected);
}

Future<void> main(List<String> arguments) async {
  final keyApplicationId = 'XXX';
  final keyClientKey = 'XXX';
  final keyParseServerUrl = 'https://parseapi.back4app.com';
  final liveQueryURL = 'wss://XXX.b4a.io';

  await Parse().initialize(
    keyApplicationId,
    keyParseServerUrl,
    clientKey: keyClientKey,
    liveQueryUrl: liveQueryURL,
    autoSendSessionId: true,
    debug: true,
    connectivityProvider: CustomParseConnectivityProvider(),
  );

  final LiveQuery liveQuery = LiveQuery();
  QueryBuilder<ParseObject> query = QueryBuilder<ParseObject>(ParseObject('Color'));
  Subscription subscription = await liveQuery.client.subscribe(query);

  subscription.on(LiveQueryEvent.create, (value) {
    print('Object: ' + value['color']);
    print((value as ParseObject).get('color'));
  });
}

附加排查项 #

如果修改后仍无法正常运行，可逐一核对以下配置：

• 确认Back4App后台已开启LiveQuery功能，且需要监听的Color类已加入LiveQuery的启用类列表
• 确认liveQueryURL填写正确，Back4App默认LiveQuery地址规则为wss://<你的应用ID>.b4a.io
• 可通过debug日志查看具体的握手错误信息，定位是否是权限或地址配置问题

内容的提问来源于stack exchange，提问作者RobbB