flutter - 如何在 Dart（Flutter）的回调函数中捕获异常？

Question

我在MyWebSocket课堂上使用 WebSocket 变量。对于听我给出一个回调函数作为参数。如果此回调函数在调用类时抛出异常MyChat，那么我无法在任何地方捕获该异常。

我的简化代码是：

class MyWebSocket {
  WebSocket _ws;
  ...
  // initialized in controller: _ws = WebSocket.connect(_some_url_);
  // everything works (connect, listen)
  ...
  void listen({void Function(dynamic) myOnListen}) {
    try {
      _ws.listen(myOnListen)
        .onError((e) => print("MyWebSocket in MyChat.onError: $e"));
    } catch (e) {
      print("Catched in MyWebSocket: $e");
    }
  }
}


class MyChat {
  MyWebSocket _chatWs = MyWebSocket();
  ...
  void initWS() {
    try {
      _chatWs.listen(myOnListen: processMsg);
    } catch (e) {
      print("Catched in MyChat: $e");
    }
  }

  void processMsg(dynamic msg) {
    if(_some_stuff_like_invalid_msg_or_not_logged_in_...)
      throw Exception("There is my Exception");
  }
}

我已经try-catch在每个可能的地方建立了捕获异常 - 没有成功，我只有未处理的异常：

E/flutter: [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] 未处理的异常：异常：有我的异常

E/颤振：#0 MyChat.processMsg

标签： flutterdart

Answer 1

请注意，您不能将传递的侦听器用作以后删除的键。为此，您可以在调用 listen() 时传递在 MyWebSocket 类中创建的新侦听器，然后使用此键删除侦听器。

class MyWebSocket {
  WebSocket _ws;
  void listen({void Function(dynamic) myOnListen, void Function(Error) onError}) {
    try {
      _ws.listen((){
        try {
          myOnListen({"label": "DATA"});
        } catch (e) {
          if(onError is Function)
          onError(e)
        }
      })
        .onError(onError);
    } catch (e) {
      print("Catched in MyWebSocket: $e");
    }
  }
}


class MyChat {
  MyWebSocket _chatWs = MyWebSocket();
  void initWS() {
    try {
      _chatWs.listen(myOnListen: processMsg, onError: (Error error){
        print("ERROR: "+error.toString());
      });
    } catch (e) {
      print("Catched in MyChat: $e");
    }
  }

  void processMsg(dynamic msg) {
    if(_some_stuff_like_invalid_msg_or_not_logged_in_...)
      throw Exception("There is my Exception");
  }
}