Use OnException to change the default behavior that occurs when an exception is not handled by application code. The OnException event handler is called automatically in the HandleException method.  

OnException only handles exceptions that occur during message processing. Exceptions that occur before or after the execution of the application's Run method do not generate OnException events. 

If an exception passes through the try blocks in the application code, the application automatically calls the HandleException method. Unless the exception object is EAbort, HandleException calls the OnException handler, if one exists. Otherwise, it calls ShowException to display a message box indicating an error occurred. 

Actions 

AfterDispatch 

TWebResponse