Trace Listeners in ASP.NET
Question
I have a library assembly that outputs trace information, and a client winforms application that adds a trace listener via app.config. If I were to use the library in ASP.NET, not configured for System.Diagnostics tracing, how could I 'catch' the trace output?
Bonus question: Can I do something with Elmah to catch and log this info? Our ASP.NET app currently uses Elmah for error logging, but that's all I know on that side of things.
Solution
write code for attaching a trace file listener programtically and enable tracing in web.config - you will be done after that
OTHER TIPS
I think that, as long as the library outputs trace information, this information could be captured with any specialized tool (like DebugView) or even a house grown tool, regardless of ASP.NET configuration.
I see this is old and answered, but.. I have just had the same issue and I came up with
Exception class for tracelistener
namespace TrueNorth.Elmah.TraceListener
{
internal class TraceInformation : Exception
{
internal TraceInformation(string message) : base(message){}
}
internal class TraceError: Exception
{
internal TraceError(string message) : base(message) { }
}
internal class TraceWarning : Exception
{
internal TraceWarning(string message) : base(message) { }
}
internal class TraceWrite : Exception
{
internal TraceWrite(string message) : base(message) { }
}
}
The listener
namespace TrueNorth.Elmah.TraceListener
{
internal class ElmahListener : System.Diagnostics.TraceListener
{
public override void TraceEvent(TraceEventCache eventCache, string source, TraceEventType eventType, int id, string format, params object[] args)
{
TraceEvent(eventCache, source, eventType, id, string.Format(format, args));
}
public override void TraceEvent(TraceEventCache eventCache, string source, TraceEventType eventType, int id, string message) //
{
Exception exception;
switch (eventType)
{
case TraceEventType.Information:
exception = new TraceInformation(message);
break;
case TraceEventType.Error:
exception = new TraceError(message);
break;
case TraceEventType.Warning:
exception = new TraceWarning(message);
break;
default:
exception = new TraceWrite(message);
break;
}
if (HttpContext.Current.Session == null)
{
ErrorLog.GetDefault(null).Log(new Error(exception));
}
else
{
ErrorSignal.FromCurrentContext().Raise(exception );
}
}
public override void TraceTransfer(TraceEventCache eventCache, string source, int id, string message, Guid relatedActivityId)
{
base.TraceTransfer(eventCache, source, id, message, relatedActivityId);
}
public override void Write(string message)
{
}
public override void WriteLine(string message)
{
}
}
}
And, the GO code ( you can use your web.config)
Tracer.Register();
blogged at http://truenorthit.co.uk/2015/04/17/trace-listener-for-elmah-asp-mvc-exception-logger/