Question

I have code that attempts a type conversion. If it fails, I want to try something else, and if that also fails, then rethrow the original exception attempted by the first conversion. The problem is that the only way I know of to rethrow is to have ‘throw;‘ sitting at the end of the catch block. What happens when I only want the rethrow to happen from within another catch block?

try 
{
    valueFromData = Convert.ChangeType(valueFromData, pi.PropertyType);
} 
catch(InvalidCastException e)
{
    Debug.WriteLine(String.Concat("Info - Direct conversion failed. Attempting to convert using String as an intermidiate type."));
    try { valueFromData = Convert.ChangeType(valueFromData.ToString(), pi.PropertyType); }
    catch { throw e; }
}

As you can see above, I have to use ‘throw e;‘, which resets the call stack.

Only workaround I’ve though of so far is (imo) gross:

bool handled = true;
... 
catch { handled = false; }
if( !handled ) throw;

Answer 1

There is no way to rethrow an exception from an outer catch block inside an inner catch block. The best way to achieve this pattern is to note whether or not the inner operation succeeded

catch (InvalidCastException e) {
  bool threw = false;
  try {
    ...
  } catch { 
    threw = true;
  }
  if (threw) {
    throw;
  }
}