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ASP.NET in a Nutshell by Matthew MacDonald, G. Andrew Duthie

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Tracing

The other useful tool provided by ASP.NET for debugging is the trace feature. Tracing allows you, through a simple configuration setting or page-level attribute, to have ASP.NET write a whole host of information about the currently executing request to the page or to a trace log. This information includes the SessionID; the time, type, and status code of the request; timing information for events such as Init, PreRender, SaveViewState, and Render; a Control Tree of all controls in the page; and the contents of the Cookies collection, the HTTP Headers, the QueryString collection (if any QueryString values were passed), the Form collection (if any form fields were passed), and the ServerVariables collection.

Essentially, tracing allows you to automatically write out the contents of all collections exposed by the classic ASP Request object, plus some really useful additional information. This allows you to examine a great deal of information about a request on a single page, which can assist greatly in debugging.

More importantly, you can also write to the trace output using the Trace.Write and Trace.Warn methods, which are exposed by the Trace property of the Page class. These methods can now be used in place of Response.Write when you determine the value of a variable on a page at a certain point in page execution or write out a notification that a certain point in the page has been hit. With Trace.Write or Trace.Warn, once you’ve disabled tracing, you can leave the statements ...

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