ASP.NET Cookbook

10.3. Pinpointing the Cause of an Exception

Problem

You want to identify problems only when an exception occurs.

Solution

Dynamically turn on page-level tracing from within the Catch block of your exception handler and write to the trace log.

In the code-behind class for the page, use the .NET language of your choice to:

1. Set Page.Trace.IsEnabled = true in the Catch block of your exception handler.

2. Write to the trace log by using a Trace.Write of the form Trace.Write("Exception","Message“, exc ).

Figure 10-3 shows the appearance of some exception information in the trace sequence. Example 10-4 through Example 10-6 show the .aspx file and VB and C# code-behind files for the application that produces this result.

Figure 10-3. Exception information in the trace sequence

Discussion

ASP.NET processes and displays trace statements only when tracing is enabled. However, what if you don’t want to see the trace log all the time, but only when an exception occurs? The answer is to turn tracing on dynamically for the page. You can then write the exception information to the trace log and debug the problem from there.

Our example that illustrates this solution is rather primitive, in that it simply forces an exception. While this is not something you would normally do in production code, it does allow us to show the infrastructure needed to control tracing at runtime.

When the exception occurs, the