C# - writing a custom exception class

[yoavyoavyoav]

Hi ,

I'm building an app that consists of a GUI that calls various functions in a DLL that I wrote (and consists of some various classes).

I am wondering how should I implement an Exception Mechanism in this project - Should I use "try" blocks only in the GUI ? (uppermost level)

and plus , if someone would kindly explain me about the "custom exception" class - how should it work exactly ?

Thanks . :-)

[Plater]

I think that .DLL files should let the exceptions pass through up to what's calling it. If the dll were sealed, it would drive you nuts to not be getting the exceptions. (So try/catch blocks in gui only I think)

As for custom exceptions:

public class myexeption:Exception
{
// ...
}
 

[yoavyoavyoav]

So let me get it straight..should the custom exception class be inside the DLL ? or in the GUI itself ? (the DLL is not sealed).

Plus - I have another problem.
one of my classes in the DLL is reading an XML file.
I want the user to be displayed with a generic "XML Parsing Error" message - nothing more than that.
if in the GUI I have the following code :

try
{
ReadXmlFunction()
}
catch(CustomExceptionClass ex)
{


}

and in the ReadXmlFunction() - an xmlException will be thrown - the catch block won't catch it - why is that ?

The custom exception class that I wrote looks like this :

public class CustomException : Exception
{
enum Type { SqlException, XmlException, Exception,Custom };

Type ExceptionType;

public CustomException(Exception ex):base()
{

switch (ex.GetType().ToString())
{
case "SqlException":
ExceptionType = Type.SqlException;
break;
case "XmlException":
ExceptionType = Type.XmlException;
break;
default:
ExceptionType = Type.Exception;
break;
}
}

public CustomException(string detail):base(detail)
{
ExceptionType = Type.Custom;
}


public string GetErrorDescription()
{
switch (ExceptionType)
{
case Type.SqlException:
return String.Format("DB Error - {0}\nError Serial # : {1}", ((SqlException)(this.GetBaseException())).Message, ((SqlException)(this.GetBaseException())).Number);

case Type.XmlException:
return String.Format("XML Parsing Error - {0}", ((System.Xml.XmlException)(this.GetBaseException() )).Message);

case Type.Exception:
return String.Format("Unrecognized General Error - {0}", Message);

case Type.Custom:
return String.Format("Reporting System Error - {0}", Message);
}
return "Critical Error recognition error. Error is : " + Message;
}

}




Thanks in advance.

[Plater]

It would be a rather nice looking package if you created your custom exception class(es, plural? if needed) and put it in the dll where you used it.
Then you could try/catch INSIDE your dll, and when you catch an exception, throw an instance of your custom exception with the amount of information you want exposed.
Then your GUI (or anything else that uses your DLL) will be catching your custom exceptions.

[yoavyoavyoav]

It would be a rather nice looking package if you created your custom exception class(es, plural? if needed) and put it in the dll where you used it.
Then you could try/catch INSIDE your dll, and when you catch an exception, throw an instance of your custom exception with the amount of information you want exposed.
Then your GUI (or anything else that uses your DLL) will be catching your custom exceptions.

Great Idea - Thanks a lot :-)