c# - 当工厂方法返回 null 时，我应该抛出什么异常？

Question

考虑一个我可能控制也可能不控制的工厂方法，作为 Func<T> 传递给另一个类:

// this.FactoryMethod is an external dependency passed into this class
// through constructor or property injection assume that it is not null
// but there is no guarantee that it will return a non-null reference.
Func<IModel> FactoryMethod;

public IModel GetPopulatedModel(int state, FileInfo someFile)
{       
   // Argument validation omitted for brevity...

   // This operation could return null.
   var model = this.FactoryMethod()
   if (model == null)
   {
      throw new SomeException("Factory method failed to produce a value.");
   }

   // Safe to assign to properties at this point.
   model.Priority = state;
   model.File = someFile;
   return model;
}

我想抛出一些指示操作失败的东西。

ArgumentNullException会产生误导，因为参数没有任何问题:

The exception that is thrown when a null reference (Nothing in Visual Basic) is passed to a method that does not accept it as a valid argument.

InvalidOperationException似乎并不正确:

The exception that is thrown when a method call is invalid for the object's current state.

将局部变量视为 the object's current state 的一部分似乎很奇怪.

抛出什么是好的异常？我很惊讶没有 OperationFailedException在 System .我应该编写自己的异常，还是有好的异常？

Answer 1

如果您觉得可供您使用的异常不足够，您可以随时创建自己的异常。

更新 虽然，我同意@TomTom 和@dtb 的可能选项。特别是 NotImplementedException 作为工厂确实没有实现