您可以查看 A Tour of the Dart Language 中的异常部分。
以下代码按预期工作（custom exception has been obtained显示在控制台中）：

class CustomException implements Exception {
  String cause;
  CustomException(this.cause);
}

void main() {
  try {
    throwException();
  } on CustomException {
    print("custom exception has been obtained");
  }
}

throwException() {
  throw new CustomException('This is my first custom exception');
}

如果你不需要具体的问题，你可以抛出一个一般性的问题，像这样：

throw ("This is my first general exception");

但最好尽可能使用特定错误。他们会告诉你更多的错误，这样你就可以找出如何修复它。

您也可以创建一个抽象异常。

• 灵感来自async包的TimeoutException（阅读Dart API和Dart SDK上的代码）。*

abstract class IMoviesRepoException implements Exception {
  const IMoviesRepoException([this.message]);

  final String? message;

  @override
  String toString() {
    String result = 'IMoviesRepoExceptionl';
    if (message is String) return '$result: $message';
    return result;
  }
}

class TmdbMoviesRepoException extends IMoviesRepoException {
  const TmdbMoviesRepoException([String? message]) : super(message);
}

尝试这个简单的自定义异常示例

class WithdrawException implements Exception{
  String wdExpMsg()=> 'Oops! something went wrong';
}

void main() {   
   try {   
      withdrawAmt(400);
   }   
  on WithdrawException{
    WithdrawException we=WithdrawException();
    print(we.wdExpMsg());
  }
  finally{
    print('Withdraw Amount<500 is not allowed');
  }
}

void withdrawAmt(int amt) {   
   if (amt <= 499) {   
      throw WithdrawException();   
   }else{
     print('Collect Your Amount=$amt from ATM Machine...');
   }   
}