The trace Section

One of the problems developers experienced with ASP was difficulty obtaining detailed debugging information. Exactly what was the page doing when an error occurred? What portions of the code had been run? ASP.NET has much improved debugging information, and the trace section of the Web.config file allows you to specify settings for the trace service. Figure 4-15 shows a page that has been run with tracing enabled and pageOutput set to true.

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Figure 4-15 : The output of the Login.aspx page shown in Listing 4-6 when tracing is enabled and pageOutput is set to true The <trace> tag supports five attributes, as described in Table 4-13.

Table 4-13 : Attributes of the <trace> Tag





Specifies whether tracing is enabled.


Specifies that tracing is enabled.


Specifies that tracing is disabled.

Table 4-13 : Attributes of the <trace> Tag




This is the default.


Specifies the number of trace requests to save on the server. The default is 10.


Specifies whether trace information should be displayed at the end of each page.


Specifies that trace output is appended to each page.



Specifies that trace output is not appended to each page. This is the default.


Sets the order of trace output.


Specifies that output is sorted by time (thus, displayed in the order the events being traced occurred). This is the default.


Specifies that output is displayed alphabeticall y by category. See the text in this

Table 4-13 : Attributes of the <trace> Tag




section for information about user-defined categories.


Specifies whether the trace viewer is available only on the host Web server.


Specifies that trace output is available only on the server console. This is the default.


Specifies that trace output is available on any client, not just the Web server.

In Figure 4-15, all trace output has a category of, and it is generated automatically by the .NET Framework, with no explicit trace code in the page source. However, this is only half the power of ASP.NET tracing. Suppose, for example, that the login page from Listing 4-6 wasn't responding the way you expected. Perhaps the following code seemed not to be working correctly:

if ((UserEmail.Value == "[email protected]") &&

(UserPass.Value == "password"))

FormsAuthentication.RedirectFromLoginPage( UserEmail.Value, false);

Msg.Text = "Invalid Credentials: Please try again";

You can use the Trace class to add user-defined trace statements in the trace output, like this:

if ((UserEmail.Value == "[email protected]") && (UserPass.Value == "password"))

Trace.Write("MyCategory", "Authenticated");

FormsAuthentication.RedirectFromLoginPage( UserEmail.Value,false);

Msg.Text = "Invalid Credentials: Please try again"; Trace.Write("MyCategory", "Invalid Credentials");

If you ran the page shown in Listing 4-6 with the modifications shown above and entered an invalid user name or password, the trace would have one "MyCategory" trace line inserted into the output, as shown in Figure 4-16.

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Figure 4-16 : Trace output with explicit trace category added In addition to the Web.config sections described in this chapter, there are a couple other sections that are not generally modified (such as the globalization section).

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