1

I want to catch an exception, and rethrow with a more specific error message:

Dictionary<string, string> m_dictionary;

try
{
     var value = m_dictionary["key"];
     ...
} 
catch ( KeyNotFoundException e )
{
     throw new KeyNotFoundException( "Error message.", e );
}

But Unity will display the original exception’s error message in the console. It gives this:

KeyNotFoundException: The given key was not present in the dictionary.

Instead of this:

KeyNotFoundException: Error message.

Is there any way to get this behavior without throwing away the call stack information of the original exception?

2

As Bonfire said the innermost exception is the most important and usually the most detailed exception. If an exception is catched by a more general system somewhere up the callstack, it usually don’t know what exactly happend. They usually just add a more general exception as outer exception and keep the inner exception.

If you actually handle the exception properly and you want to provide a more detailed exception, you might want to remove the inner exception and just throw your customized exception.

However This approach is actually bad design, especially for realtime applications. A try-catch block adds quite a bit of overhead. Exceptions should never be used as a way of flowcontrol. If an exception can be avoided you should go that route.

In the case of a dictionary the method which does this is TryGetValue

string value;
if (m_dictionary.TryGetValue("key", out value))
{
    // key was found, value has been filled.
}
else
{
    // key wasn't found, take further actions.
    // Either fill "value" manually if possible or throw an exception if there's no way around.
}

Finally some information on when to use exceptions and when not.