在Dart中扩展Exception类 [英] Extending the Exception class in Dart

问题描述

当我尝试扩展Exception类并且无法弄清楚原因时，我总是收到错误消息。
这是我的自定义异常的代码：

I keep getting an error when I try to extend the Exception class and can't figure out why. Here is the code for my custom exception:

class MyException extends Exception {
  String msg;
  MyException(this.msg);
  String toString() => 'FooException: $msg';
}

该错误在构造函数周围解决。它抱怨说生成的构​​造函数'Exception（[dynamic message]）-> Exception'可能是工厂发现的。我该如何解决？

The error resolves around the constructor. It complains that "The generative constructor 'Exception([dynamic message]) -> Exception' expected, but factory found". How do I fix this?

推荐答案

您几乎完全正确。您需要实现异常，而不是扩展它。这应该起作用：

You have it almost right. You need to implement Exception rather than extend it. This should work:

class MyException implements Exception {
  final String msg;
  const MyException(this.msg);
  String toString() => 'FooException: $msg';
}

您不必制作 msg final或构造函数 const ，但可以。这是Exception类的实现示例（来自dart：core库）：

You don't have to make msg final or the constructor const, but you can. Here is an example of an implementation of the Exception class (from the dart:core library):

class FormatException implements Exception {
  /**
   * A message describing the format error.
   */
  final String message;

  /**
   * Creates a new FormatException with an optional error [message].
   */
  const FormatException([this.message = ""]);

  String toString() => "FormatException: $message";
}

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