Exception Handling Tip

Tulsi · May 30th, 2013, 01:03 PM

Hi Imar,

I'm reviewing the tips at the end of Ch. 18 and am trying to get a better understanding of the last tip,

Quote:

"Be as explicit as possible with the Exception types you catch in Try/Catch blocks. Try to avoid catching generic Exception types and set up multiple, explicit Catch blocks for each specific type you anticipate."

Using the exercise on "Handling Exceptions" and the ContactForm.ascx (p. 663) as an example, how would you know what specific exceptions to catch for sending emails and how would you change this example?

Thanks,
Tulsi

Imar · May 30th, 2013, 02:25 PM

Hi Tulsi,

Take a look at page 660 for a concrete example. That code catches an SmtpException as well as a generic Exception. You could further divide this by catching SmtpFailedRecipientException and SmtpFailedRecipientsException:

http://msdn.microsoft.com/en-us/libr...exception.aspx

To find out the Exceptions that can be thrown, consult the MSDN documentation. Here's an example of the Send method of the SmtpClient class: http://msdn.microsoft.com/en-us/library/swas0fwc.aspx

In this case, I would probably just handle SmtpException as all you want to do is tell the user something went wrong while sending the message. The first three exceptions can typically be avoided by constructing a valid message object.

Hope this helps,

Imar

Tulsi · June 5th, 2013, 01:17 PM

Hi Imar,

Thank you for directing me to this link!

Until now, I've always been confused as to how one would know what exceptions to look for. This link surely clarifies things.

After reviewing ContactForm.acx again, I noticed that there are more exceptions that may be generated in the following code in SendButton_Click() when trying to read the ContactForm.txt file:

Code:

if (string.IsNullOrEmpty(mailBody))
            {
                string fileName = Server.MapPath("~/App_Data/ContactForm.txt");
                mailBody = File.ReadAllText(fileName);
                Cache.Insert("ContactFormMailBody", mailBody, new System.Web.Caching.CacheDependency(fileName));                
            }

Should this code be wrapped in it's own try/catch block separate from the try/catch block for sending the actual email? What is the correct way to handle this type of situation?

Tulsi

Imar · June 6th, 2013, 04:11 AM

Hi Tulsi,

It depends ;-)

In my opinion, the fact that the mail body file can't be found or read is a software or configuration error that won't go away automatically. This means there's no point in showing the user a message like "Ooops, something went wrong; please try again:.

Instead, you want to be notified of this error using the global error handler in Global.asax (or better yet, with ELMAH). The easiest thing to do is not handle this exception in the contact control, but rely on custom errors. This way, the user gets the generic Error 500 page and the error message is logged.

In general, you should catch exceptions that you know how to handle, and let the others bubble up as unhandled exceptions and log them at the global level.

Hope this helps,

Imar

Tulsi · June 6th, 2013, 09:33 AM

This was very helpful:) Thank you so much for the detailed and quick replies.

This has made the learning process so much easier and exciting!

I'm continuing to the chapter on "Deploying your Web Site" - Very excited!!

Tulsi

Imar · June 6th, 2013, 10:34 AM

>> I'm continuing to the chapter on "Deploying your Web Site" - Very excited!!

Excellent. Almost done. Congratulations.... ;-)

Imar