Runtime exceptions

The XmlSerializer throws exceptions to indicate all sorts of problems. In most cases an exception handler will catch a System.InvalidOperationException thrown in Serialize() or Deserialize(), which makes the StackTrace property useless because it does not offer any more insight into the root cause of the exception. To make matters worse, the exception’s Message property only yields very generic information. If we are trying to serialize an undeclared type for example the Serialize() method would throw an exception with the following message:

There was an error generating the XML document. This message is annoying at best, because we already figured that much when we saw an exception and doesn’t help us troubleshooting the problem. The trick to get to the “real information” about the problem is to examine the exception’s InnerException property, which contains very detailed information about the problem and where it occurred.

The InnerException’s message is usually very descriptive, pinpoints the problem and, in many cases, even offers a possible solution. When we are trying to serialize an undeclared type the InnerExcpetion reads something like this: The type XmlSerializationApp.XmlCar was not expected. Use the XmlInclude or SoapInclude attribute to specify types that are not known statically.

The following listing demonstrates how to set up the exception handler and how to access the InnerException property.

4           Listing 9.9 Handling an Exception from the XmlSerializer and displaying the embedded information

using System;

public static ParkingLot DeserializeParkingLot( XmlReader reader )

{

  ParkingLot lot = null;

  try

  {

    XmlSerializer ser = new XmlSerializer( typeof(ParkingLot));

    lot = (ParkingLot) ser.Deserialize( reader );

  }

  catch( Exception ex )               |#1

  {                                   |

    DumpException( ex );              |

  }                                   |

  return lot;

}

public static void DumpException( Exception ex )

{

  WriteExceptionInfo( ex );                     |#2

  if( null != ex.InnerException )               |

  {                                             |

    WriteExceptionInfo( ex.InnerException );    |

  }

}

public static void WriteExceptionInfo( Exception ex )

{

  Console.WriteLine( "--------- Exception Data ---------" );        |#3

  Console.WriteLine( "Message: {0}", ex.Message );                   |

  Console.WriteLine( "Exception Type: {0}", ex.GetType().FullName ); |

  Console.WriteLine( "Source: {0}", ex.Source );                     |

  Console.WriteLine( "StrackTrace: {0}", ex.StackTrace );            |

  Console.WriteLine( "TargetSite: {0}", ex.TargetSite );             |

}

 (annotation) <#1  Catch all exceptions>

(annotation) <#2  Display the properties for the exception and its InnerException>

(annotation) <#3  Display all properties with information about the problem>