Question

When using a Trace.Listener can anyone tell me why the

Trace.Write(string message, string category) 

doesn’t pass the category string to the TraceFilter when the method

Trace.Write(object o, string category)

does pass the category string to the ShouldTrace method. Below are decompiles of both methods from Reflector. Just wondering why the .NET team would do something on one method and not on another method.

public virtual void Write(object o, string category)
{
    if ((this.Filter == null) || 
 this.Filter.ShouldTrace(null, "", TraceEventType.Verbose, 0, category, null, o))
    {
        if (category == null)
        {
            this.Write(o);
        }
        else
        {
            this.Write((o == null) ? "" : o.ToString(), category);
        }
    }
}

and then the string method.

public virtual void Write(string message, string category)
{
    if ((this.Filter == null) || 
         this.Filter.ShouldTrace(null, "", TraceEventType.Verbose, 0, message))
    {
        if (category == null)
        {
            this.Write(message);
        }
        else
        {
            this.Write(category + ": " + ((message == null) ? string.Empty : message));
        }
    }
}

Answer 1

The call to this.Write in the first overload

this.Write((o == null) ? "" : o.ToString(), category);

delegates the actual output to the second overload

public virtual void Write(string message, string category)

All of the formatting for the output is then centralized in the second overload:

this.Write(category + ": " + ((message == null) ? string.Empty : message));

By centralizing the actual formatting in this way, changing the formatting in a single place will change all trace output formatting. It’s an application of DRY principles.