C# : Better way to code this?

Question

I have a block of code to handle exceptions in my application, which uses an if/else block to obtain the message content.
My code is as follows:

// define variable to hold exceptions...
var exceptionMessage = new StringBuilder();  
// based on the exception type...  
if (expType == typeof(EntityValidationException))  
{  
    // append the relevant message to the text...  
    exceptionMessage.Append(exception.InnerException.Message);  
}  
else if (expType == typeof(ValidationException))  
{  
    // This is the type of error generated when entities are validated  
    var validationException = (ValidationException)exception;  
    exceptionMessage.Append(validationException.InnerException.Message);  
}  
else if (expType == typeof(DomainSecurityException))  
{  
    // These are security breaches  
    var domainSecurityException = (DomainSecurityException)exception;  
    exceptionMessage.Append(domainSecurityException.InnerException.Message);  
}  
else if (expType == typeof(DomainInternalMessageException))  
{  
    // These are the type of errors generated a System.Exception occurs and is  
    // converted by the exception handling policy to a more friendly format  
    var domainInternalMessageException = (DomainInternalMessageException)exception;  
    exceptionMessage.Append(domainInternalMessageException.ExceptionMessage);  
}
else  
{  
    exceptionMessage.AppendFormat(ErrorMessagesRes.Standard_Error_Format, "Unknown error", exception.InnerException.Message);   
}  
// this shows the message as an alert popup...  
this.DisplayJavascriptMessage(exceptionMessage.ToString());

This has been improved from the original version, but just want to see if there is a neater, more re-usable solution to this code.
Thanks in advance
Martin

Answer 1

Assuming that this is a routine which gets passed an exception object (and is not directly involved in a try catch block) and assuming the "exception" object derives eventually from Exception, you could concise your code a bit to do

// define variable to hold exceptions...
            var exceptionMessage = new StringBuilder();

            // based on the exception type...  
            if (exception is EntityValidationException || exception is ValidationException || exception is DomainSecurityException)
            {
                // append the relevant message to the text...  
                exceptionMessage.Append(exception.InnerException.Message);
            }

            else if (expType == typeof(DomainInternalMessageException))
            {
                // These are the type of errors generated a System.Exception occurs and is  
                // converted by the exception handling policy to a more friendly format  
                var domainInternalMessageException = (DomainInternalMessageException)exception;
                exceptionMessage.Append(domainInternalMessageException.ExceptionMessage);
            }
            else
            {
                exceptionMessage.AppendFormat(ErrorMessagesRes.Standard_Error_Format, "Unknown error", exception.InnerException.Message);
            }
            // this shows the message as an alert popup...  
            this.DisplayJavascriptMessage(exceptionMessage.ToString());