Overriding System.Diagnostics.Trace.WriteLine to log to a file

Question

This may be more of an OOP concept question, but here's what I'd like to do.

I have an application that outputs debug information using System.Diagnostics.Trace.WriteLine so it can be viewed with DebugView.

I'd like to override/extend (not sure of the proper terminology) this method to log the text to a file instead, or maybe in addition to the Trace output. This would allow me to write a new WriteLine method for my app, and I could leave all my other System.Diagnostics.Trace.WriteLine statements unchanged throughout the rest of the application.

So how would I go about changing the behavior of this method within my VB.Net app?

Answer 1

Are you absolutely committed to still using Trace? If not, I'd use a more fully-featured logging system such as Log4Net.

However, if you really want to use Trace then you can reconfigure the TraceListeners used with an app.config file. The TraceListener MSDN docs give an example somewhat like this:

<configuration>
  <system.diagnostics>
    <trace autoflush="false" indentsize="4">
      <listeners>
        <add name="fileLogger" 
             type="System.Diagnostics.TextWriterTraceListener" 
             initializeData="LogFile.log" />
        <remove name="Default" />
      </listeners>
    </trace>
  </system.diagnostics>
</configuration>

TextWriterTraceListener will dump logs to the given file. (There are other options available too.)

Alternatively, you can do this programmatically:

Trace.Listeners.Add(new TextWriterTraceListener("foo.log"));

Note that you may need to explicitly flush the traces before your app exits, either with:

Trace.Flush();

or the more complicated:

foreach (TraceListener listener in Trace.Listeners)
{
    listener.Flush();
}

(I only mention it because I had to when testing this!)

EDIT: As noted in comments, if you're happy for the listener to be flushed after every write (which avoids having to flush at the end, but may harm performance) you can set Trace.AutoFlush to true (including in the XML - see the autoflush attribute).