Introduction to Exception Handling Block

Application blocks are Microsoft recommended patterns and practices which address some of the most common scenarios like logging, caching, exception handling, dependency injection and so on. All the application blocks are bundled together under an umbrella called as the Microsoft Enterprise Library. The current version of Enterprise Library is 5.0 (http://msdn.microsoft.com/en-us/library/ff648951.aspx).

Why use Enterprise Library ?

1. Address most common scenarios
2. Can be added to any application easily
3. It is collection of reusable components and best practices
4. Is configuration driven
5. They can be easily extended

I will focus on Exception Handling Block in this article.

Steps to include Exception Handling Block :

1. Download Enterprise Library 5.0
2. Add reference to the following dlls :

Microsoft.Practices.EnterpriseLibrary.Common and Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.

3. Within your class, include namespaces :

        using Microsoft.Practices.EnterpriseLibrary.ExceptionHandling;
        using Microsoft.Practices.EnterpriseLibrary.Common.Configuration;

4. Then, policies need to be defined for your application

Policies may be like whether you want to rethrow exception or throw new exception or just handle the exception. This is done by setting postHandlingAction attribute. We can also have handlers associated with the policy like if we are rethrowing an exception what should be the new exception, should we wrap the exception or should we replace the exception. We can as well log the exception to a file or database. Again there are lot of extensible features.

The beauty however lies in the fact that this is completely configuration driven. There is a tool called “EntLibConfig.exe” within the downloaded Enterprise Library folder which has UI for configuring all of the Enterprise Libraries.

5. Once policies are defined, then we have to get handle to instance of appropriate classes (Exception Manager here) and then use it accordingly. The code snippet will be as shown below :

   try
            {
                _input1 = Convert.ToInt32(textBox1.Text);
                _input2 = Convert.ToInt32(textBox2.Text);
            }
            catch (Exception ex)
            {
                  var exceptionManager = EnterpriseLibraryContainer.Current.GetInstance<ExceptionManager>();
                  exceptionManager.HandleException(ex, "UIPolicy");
            }

Here UIPolicy is a defined policy for exception handling.

I am attaching code snippet for the same. App.config has the UIPolicy defined and also I have enabled Logging using Logging Application Block.

Happy coding!