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.

当您没有特定的代码来处理当前异常时，或者当您有处理特定错误情况的逻辑但想要跳过所有其他情况时，通过throw重新抛出异常非常有用。

例子:

string numberText = "";
try
{
    Console.Write("Enter an integer: ");
    numberText = Console.ReadLine();
    var result = int.Parse(numberText);

    Console.WriteLine("You entered {0}", result);
}
catch (FormatException)
{
    if (numberText.ToLowerInvariant() == "nothing")
    {
        Console.WriteLine("Please, please don't be lazy and enter a valid number next time.");
    }
    else
    {
        throw;
    }
}    
finally
{
    Console.WriteLine("Freed some resources.");
}
Console.ReadKey();

然而，还有另一种方法，在catch块中使用条件子句:

string numberText = "";
try
{
    Console.Write("Enter an integer: ");
    numberText = Console.ReadLine();
    var result = int.Parse(numberText);

    Console.WriteLine("You entered {0}", result);
}
catch (FormatException) when (numberText.ToLowerInvariant() == "nothing")
{
    Console.WriteLine("Please, please don't be lazy and enter a valid number next time.");
}    
finally
{
    Console.WriteLine("Freed some resources.");
}
Console.ReadKey();

这种机制比重新抛出异常更有效，因为 的。net运行时不需要重新构建异常对象 然后再扔出去。

你不会想要抛出ex -，因为这会丢失调用堆栈。参见异常处理(MSDN)。

是的，尝试…Catch没有做任何有用的事情(除了丢失调用堆栈之外——所以它实际上更糟——除非出于某种原因您不想公开此信息)。

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;
    }

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);
  }
}

我使用如下代码的主要原因:

try
{
    //Some code
}
catch (Exception e)
{
    throw;
}

是我可以在catch中有一个断点，它有一个实例化的异常对象。在开发/调试时，我经常这样做。当然，编译器会对所有未使用的e给出警告，理想情况下，应该在发布版本之前删除它们。

不过，在调试过程中它们很好用。