首先，本文中代码的实现方式是邪恶的。Throw ex将重置异常中的调用堆栈，直到该Throw语句丢失有关异常实际创建位置的信息。

其次，如果你只是像那样接住然后再扔，我认为没有额外的价值。上面的代码示例如果没有try-catch也一样好(或者，考虑到throw ex位，甚至更好)。

但是，在某些情况下，您可能希望捕获并重新抛出异常。日志可能是其中之一:

    try 
    {
        // code that may throw exceptions    
    }
    catch(Exception ex) 
    {
        // add error logging here
        throw;
    }

不要这样做，

try 
{
...
}
catch(Exception ex)
{
   throw ex;
}

您将丢失堆栈跟踪信息…

无论做什么,

try { ... }
catch { throw; }

OR

try { ... }
catch (Exception ex)
{
    throw new Exception("My Custom Error Message", ex);
}

您可能想要重新抛出的原因之一是，如果您正在处理不同的异常，对于 如。

try
{
   ...
}
catch(SQLException sex)
{
   //Do Custom Logging 
   //Don't throw exception - swallow it here
}
catch(OtherException oex)
{
   //Do something else
   throw new WrappedException("Other Exception occured");
}
catch
{
   System.Diagnostics.Debug.WriteLine("Eeep! an error, not to worry, will be handled higher up the call stack");
   throw; //Chuck everything else back up the stack
}

人们没有提到的一点是，虽然。net语言并没有真正做出适当的区分，但当异常发生时是否应该采取行动，以及是否会解决它，实际上是两个不同的问题。在许多情况下，应该根据无法解决的异常采取行动，在某些情况下，“解决”异常所必需的只是将堆栈展开到某个点——不需要进一步的行动。

Because of the common wisdom that one should only "catch" things one can "handle", a lot of code which should take action when exceptions occur, doesn't. For example, a lot of code will acquire a lock, put the guarded object "temporarily" into a state which violates its invariants, then put it object into a legitimate state, and then release the lock back before anyone else can see the object. If an exception occurs while the object is in a dangerously-invalid state, common practice is to release the lock with the object still in that state. A much better pattern would be to have an exception that occurs while the object is in a "dangerous" condition expressly invalidate the lock so any future attempt to acquire it will immediately fail. Consistent use of such a pattern would greatly improve the safety of so-called "Pokemon" exception handling, which IMHO gets a bad reputation primarily because of code which allows exceptions to percolate up without taking appropriate action first.

In most .NET languages, the only way for code to take action based upon an exception is to catch it (even though it knows it's not going to resolve the exception), perform the action in question and then re-throw). Another possible approach if code doesn't care about what exception is thrown is to use an ok flag with a try/finally block; set the ok flag to false before the block, and to true before the block exits, and before any return that's within the block. Then, within finally, assume that if ok isn't set, an exception must have occurred. Such an approach is semantically better than a catch/throw, but is ugly and is less maintainable than it should be.

当您为库或dll编程函数时，这可能很有用。

此重抛出结构可用于有目的地重置调用堆栈，以便从函数本身获取异常，而不是从函数内部的单个函数中查看抛出的异常。

我认为这样做只是为了让抛出的异常更清晰，并且不会进入库的“根”。

这不是完全等同于不 处理异常?

不完全一样，不一样。它重置异常的堆栈跟踪。 尽管我同意这可能是一个错误，因此是一个糟糕代码的例子。

重新抛出异常的一个有效原因可能是您想要向异常添加信息，或者可能将原始异常包装在您自己制作的异常中:

public static string SerializeDTO(DTO dto) {
  try {
      XmlSerializer xmlSer = new XmlSerializer(dto.GetType());
      StringWriter sWriter = new StringWriter();
      xmlSer.Serialize(sWriter, dto);
      return sWriter.ToString();
  }
  catch(Exception ex) {
    string message = 
      String.Format("Something went wrong serializing DTO {0}", DTO);
    throw new MyLibraryException(message, ex);
  }
}