Tracing in ASP.NET
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by Phil Winstanley
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Which part of “False” do you not understand?

Remember way back to the top of the article, where I showed you an excerpt from the .NET SDK Documentation, it said “Trace statements are processed and displayed only when tracing is enabled.”?

It Lies. J

We can prove this by setting the Trace property on a page to False and then calling a trace command that will cause an exception, for example referencing an object that doesn’t exist such as a Querystring value: -

private void Page_Load(object sender, System.EventArgs e)

{

          Trace.Write(Request.QueryString["Doesn'tExist"].ToString());

}

 

Calling this when Trace is enabled causes an exception to occur: -

Server Error in '/intranet' Application.


Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

 
Line 21: {
Line 22:         //Some fake business logic
Line 23:         Trace.Write(Request.QueryString["Doesn'tExist"].ToString());
Line 24: }
Line 25: 


Source File: c:\inetpub\wwwroot\intranet\default.aspx.cs    Line: 23

Stack Trace:

 
[NullReferenceException: Object reference not set to an instance of an object.]
   intranet._default.Page_Load(Object sender, EventArgs e) in c:\inetpub\wwwroot\intranet\default.aspx.cs:23
   System.Web.UI.Control.OnLoad(EventArgs e) +67
   System.Web.UI.Control.LoadRecursive() +29
   System.Web.UI.Page.ProcessRequestMain() +718

 


Version Information: Microsoft .NET Framework Version:1.0.3705.288; ASP.NET Version:1.0.3705.288

This means that the statement “Trace statements are processed and displayed only when tracing is enabled.” is obviously a blatant lie.

This is also important in terms of costly operations, lets say you’ve put a large loop in to your page and it’s outputting data to the Trace log so you can debug it – why do we need to call this when Trace is turned off?

A solution is provided in the form of Trace.IsEnabled(), we can check to see if Tracing is enabled before we run the Trace commands, like this: -

private void Page_Load(object sender, System.EventArgs e)

{

          if (Trace.IsEnabled)

          {

                   Trace.Write(Request.QueryString["Doesn'tExist"].ToString());

          }

}

Now, that means we now have to write four lines of code for every Trace we have to write, which is really not an inviting thought – Trace is supposed to make things EASIER not HARDER!

Let’s also add some error handling to our Trace command to make sure that even when we get errors we can handle them properly: -

private void Page_Load(object sender, System.EventArgs e)

{

          if (Trace.IsEnabled)

          {

                   try

                   {

                             Trace.Write(Request.QueryString["Doesn'tExist"].ToString());

                   }

                   catch (Exception ex)

                   {

                             Trace.Warn("Trace","Exception",ex);

                   }

          }

}

Now, our simple 1 line Trace.Write call is 11 lines long! Messy I hope you’ll agree.


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User Comments

Title: ateeq   
Name: helo
Date: 2012-12-18 4:43:34 AM
Comment:
flksd fsdjlk fjds djs sda s sadlj falk asldfj as
Title: Programmer   
Name: Terence
Date: 2004-07-16 12:42:52 PM
Comment:
It looks like the last post cut some of the code off... but you get the idea. Terence.
Title: Programmer   
Name: Terence
Date: 2004-07-16 12:40:45 PM
Comment:
Nice job Phil. I tranlated your C# code to vb.net for those who are interested in that. Cheers. Terence
'Translated from C# to VB.net.
'July 16, 2004
'Terence J Wehle
'We use shared Methods in this translation so that creating an instance
'of the object is not necessary. This is appropriate since
'each methods is acting only on passed in parameters.

'In this article, Phil Winstanley proves that contrary to the
'NET SDK documentation that “Trace statements are processed and displayed
'only when tracing is enabled.”, the statements are in fact processed,
'although not displayed. If you have many such statements, particularly
'in a loop, this could slow things down for the page even thought the
'Trace is set to "False". This solution checks first whether tracing
'is enable before making the call and thus save resources. It is a
'wrapper for the trace calls.
'---------------------
Imports System
Namespace TJW


Public Class Trace

Public Sub Write(ByVal Message As String)

If (System.Web.HttpContext.Current.Trace.IsEnabled) Then

Try
System.Web.HttpContext.Current.Trace.Write(Message.ToString())
Catch e As Exception
System.Web.HttpContext.Current.Trace.Warn("Trace", "Write", e)
End Try

End If

End Sub

Shared Sub Write(ByVal Category As String, ByVal Message As String)

If (System.Web.HttpContext.Current.Trace.IsEnabled) Then

Try
Throw New Exception("This is a bogus error")
System.Web.HttpContext.Current.Trace.Write(Category.ToString(), Message.ToString())
Catch e As Exception
System.Web.HttpContext.Current.Trace.Warn("Trace", "Write", e)
End Try

End If

End Sub

Public Sub Write(ByVal Category As String, ByVal Message As Stri






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