| Printable Version
The Use Of InnerException
By Loek van den Ouweland
An unknown error with
an unknown description has occurred. Please remain calm while the appropriate
authorities are on their way.
Do you recognize these kind of
errors? Ever wondered how you can manage your errors in a way you can track 'm
down from their source to the point you need to show them? The solution is
simple. Use the innerexception from the standard ApplicationException
object. In the next example I use a custom Exception because i need some
additional info but it will also work fine
with a default Exception.
STEP1: Create my own exception class wich
contains extra properties (sender and details). This class also contains a
ShowError method that loads a form that will show the error message(s). The
ToString is overridden so it can show my extra added information.
//-------------------------------------------------------------------
//
// Author : Loek van den Ouweland
// EMail : lvdo@in2net.nl
// Creation date : July 2003
//
//-------------------------------------------------------------------
using System;
using System.Windows.Forms;
namespace LootAtThisError
{
public class LookException : ApplicationException
{
private string mSender;
private string mDetails;
public
LookException (string message, Exception ex, string sender, string details) : base (message,ex)
{
mSender=sender;
mDetails=details;
}
public string Sender
{
get
{return mSender;}
}
public string Details
{
get
{return mDetails;}
}
public void ShowError()
{
FException
fe=new FException(this);
fe.ShowDialog();
}
public override
string ToString()
{
string errortext="Message: " + this.Message + Environment.NewLine +
"Sender : " + mSender + Environment.NewLine +
"Details: " + mDetails + Environment.NewLine;
return errortext;
}
}
}
STEP2: The first error that will appear is
always of type: Exception. Just catch this bad boy and throw your own:
string
sql="this will certainly raise an arror";
.
.
catch (Exception ex)
{
throw
new
LookException (ex.Message,ex,ex.Source,sql);
}
STEP3: Just catch and rethrow your error as
many times as you want. These are LookExceptions:
catch
(LookException ex)
{
throw
new
LookException ("my
friendly error message",ex,"it happened here","extra details
like ID's");
}
STEP4: At last, i.e. in your presentation
layer, just catch the LookException
and show the error:
catch (LookException
ex)
{
ex.ShowError();
}
catch
(Exception ex)
{
// also: always catch a default Exception just to make sure no-one
escapes!
}
STEP5: Create a form that's capable of showing
the error. To show the error with all it's innerexceptions, pass the exception
to the form (store it in mException) and do something like this:
private void
FException_Load(object sender,
System.EventArgs e)
{
txtMessage.Text=mException.Message;
Exception inex=mException;
while (inex!=null)
{
txtDetails.Text+=
inex.ToString() + Environment.NewLine;
txtDetails.Text+=
Environment.NewLine + "<*==---------------------------==*>" +
Environment.NewLine;
inex=inex.InnerException;
}
}
CONCLUSION: The trick here is that every time
you throw an error, you can pass the 'just catched' error along with it. Finally
show the exception plus all innerexceptions by calling their ToString-functions.
Happy catching!
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