.NET Tip: Throwing Custom Exceptions

Creating your own custom exceptions is very easy and allows your code to be more explicit as well as being able to provide more user-friendly error messages. To show how to use custom exceptions, I will use connecting to a database as an example. Connecting to a database is something your application probably does on a regular basis and is a common point of failure. The first step is to create the class for your custom exception that inherits from another exception class. In this case, you'll create an UnableToOpenDatabaseException based on the Exception class. Here is what the custom exception class looks like:

public class UnableToOpenDatabaseException : Exception
{
   public UnableToOpenDatabaseException()
      : base()
   {
   }

   public UnableToOpenDatabaseException(string Message)
      : base(Message)
   {
   }

   public UnableToOpenDatabaseException(string Message,
                                        Exception InnerException)
      : base(Message, InnerException)
   {
   }

   protected UnableToOpenDatabaseException(SerializationInfo Info,
                                           StreamingContext Context)
      : base(Info, Context)
   {
   }
}

To use the custom exception, you need to check to see whether an exception is thrown when you attempt to connect to the database. In my case, I'm connecting to SQLServer, so I will check to see if a SQLException was thrown. If a SQLException is thrown, I throw the new UnableToOpenDatabaseException, passing the original exception to the new one. If an exception other than a SQLException is thrown, I simply rethrow the original exception.

using (SqlConnection CN =
   new SqlConnection("*** Your connection string here ***"))
{
   try
   {
      CN.Open();
   }
   catch (SqlException ex)
   {
      // Throw the custom UnableToOpenDatabaseException
      throw new UnableToOpenDatabaseException("Unable to open
         database connection.", ex);
   }
   catch (Exception ex)
   {
      // Rethrow the original exception
      throw;
   }
}

This allows the calling code to take advantage of the new exception while still allowing it to access all of the original exception information if needed. This example lumped any type of SQLException under the new exception type. If you needed more granularity in your exceptions, you could create custom exceptions for different failure conditions.

About the Author

Jay Miller is a Software Engineer with Electronic Tracking Systems, a company dedicated to robbery prevention, apprehension, and recovery based in Carrollton, Texas. Jay has been working with .NET since the release of the first beta and is co-author of Learn Microsoft Visual Basic.Net In a Weekend. Jay can be reached via email at jmiller@sm-ets.com.



Comments

  • There are no comments yet. Be the first to comment!

Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • Live Event Date: May 13, 2105 @ 1:00 p.m. ET / 10:00 a.m. PT Your data is a valuable asset that can quickly transform into a liability when breached. Organizations often become hung up on combating external breaches, while the insider threat doesn't get the attention it deserves. To manage both external and internal threats, new approaches to security are required, particularly in regards to authorized internal users who have legitimate access to sensitive information. Join TITUS and a guest speaker from …

  • On-demand Event Event Date: March 19, 2015 The 2015 Enterprise Mobile Application Survey asked 250 mobility professionals what their biggest mobile challenges are, how many employees they are equipping with mobile apps, and their methods for driving value with mobility. Join Dan Woods, Editor and CTO of CITO Research, and Alan Murray, SVP of Products at Apperian, as they break down the results of this survey and discuss how enterprises are using mobile application management and private app stores to …

Most Popular Programming Stories

More for Developers

RSS Feeds

Thanks for your registration, follow us on our social networks to keep up-to-date