存在System.ArgumentException的捕获块，但是无论如何都没有捕获到异常，为什么？

Question

I have this code:

       if (typeof(Enum).IsAssignableFrom(typeof(T)))
        {
            try
            {
                return (T)Enum.Parse(typeof(T), text);
            }
            catch (ArgumentException e)
            {
                return default(T);
            }
        }

However I received the following exception:

A first chance exception of type 'System.ArgumentException' occurred in mscorlib.dll Additional information: Requested value 'ABC' was not found

How is that possible? Why is the catch block not working?

Answer 1

Why is the catch block not working?

The catch block is working perfectly fine, it's just that you are looking this in Visual Studio debugger. That's what a first chance exception means. When you debug, all exception are shown in VS, it's just that a first chance exception might disappear if you have a proper catch clause. And by the way you could configure VS not to show them.

Oh and just a side note: in .NET 4.0 there's the Enum.TryParse method so you don't even need to try and catch in this particular snippet.

Answer 2

A first-chance notification is just to let the debugger know that the exception was thrown - this happens before any catch frames are considered. So in short your exception is (probably) caught.