Beginning ASP.NET 3.5: In C# and VB

17.5. Tracing Your ASP.NET Web Pages

Without tracing, finding out the values of variables, objects, the execution path your code follows, and so on at run time is problematic at best. You would probably add a Label control to the page, and then write information to it like this:

VB.NET

Dim value2 As Double = Convert.ToDouble(txtValue2.Text)
lblDebug.Text &= "The value of value2 = " & value2.ToString() & "<br />"

C#

double value2 = Convert.ToDouble(txtValue2.Text);
lblDebug.Text += "The value of value2 = " + value2.ToString() + "<br />";

Although this certainly works, it's quite cumbersome. First, you need to write a lot of code to make this work. Secondly, you end up with an ugly Label control in your page that you shouldn't forget to remove when you're done doing your debugging or tracing. And finally, when you're ready, you should remove all the code that sets the lblDebug label. You could take the easy way out by setting the Label control's Visible property to False, but you would still take the performance hit of assigning the text to the Label control.

Tracing in ASP.NET solves all of these problems. It lets your pages, controls, and code write information to a central location, called the Trace, which can then be shown in the browser. Tracing is built into the ASP.NET Framework, which means you can use it without any manual coding. Additionally, you can add your own information to the trace. In the following section you see how to use the built-in Tracing capabilities, giving ...