Question

I have a custom exception class which contains some additional fields. I want these to be written out in the ToString() method, but if I implement my own ToString(), I loose some other useful stuff (like writing the exception type name, the inner exception data and the stack trace).

What is the best way/pattern to implement your own ToString() method for such exceptions? Ideally it should reuse the existing mechanism, but be formatted in way similar to the default ToString() implementation.

UPDATE: prepending or appending my custom fields to the base.ToString() text isn’t ideal IMHO, for example

PimTool.Utilities.OERestServiceUnavailableException: test ---> System.InvalidOperationException: inner message
   --- End of inner exception stack trace ---
   at PimTool.Tests.Services.OE.OERestClientTests.ExceptionsLogging() in D:\svn\NewPimTool\PimTool.Tests\Services\OE\OERestClientTests.cs:line 178, 
   StatusCode=0, message='test', requestId='535345'

means the custom fields are written at the end of the (potentially long) exception description.
On the other hand, I want the exception type to be the first information written in the description.

UPDATE 2: I’ve implemented a solution for this, look for my own answer below.

Answer 1

OK, this is what I came up with. I’ve implemented an extension class which replicates the original mechanism for formatting exceptions, but with a twist: a custom Action delegate which provides a plug-in for formatting custom fields:

public static class ExceptionFormatterExtensions
{
    public static string ExceptionToString (
        this Exception ex, 
        Action<StringBuilder> customFieldsFormatterAction)
    {
        StringBuilder description = new StringBuilder();
        description.AppendFormat("{0}: {1}", ex.GetType().Name, ex.Message);

        if (customFieldsFormatterAction != null)
            customFieldsFormatterAction(description);

        if (ex.InnerException != null)
        {
            description.AppendFormat(" ---> {0}", ex.InnerException);
            description.AppendFormat(
                "{0}   --- End of inner exception stack trace ---{0}",
                Environment.NewLine);
        }

        description.Append(ex.StackTrace);

        return description.ToString();
    }
}

Now you can use this method in your own ToString() implementations without duplicating the formatting code:

    public override string ToString()
    {
        return this.ExceptionToString(
            description =>
            {
                description.AppendFormat(
                    ", HttpStatusCode={0}, RequestId='{1}'", 
                    httpStatusCode, 
                    RequestId);
            });
    }