Section 2.8. Diagnose Exceptions

2.8. Diagnose Exceptions

The new Exception Assistant gives you a strong head start on figuring out why your code threw an exception and what to do about it.

2.8.1. How do I do that?

The new Visual Studio 2005 Exception Assistant is always turned on; you don't have to do anything special (except for throwing an exception) to call it into action. When an exception is thrown, the editor switches to Break mode, the statement that caused the exception is highlighted, and the Exception Assistant leaps forward with suggestions for what to do.

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Note: The Exception Assistant helps you diagnose why an exception was thrown.

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To see this at work, go back to ExamineXML, the project you created for the "Visualize XML Data" lab, and in the source code change the name of the file to be read by StreamReader from BookList.xml to BadFileName.xml, a nonexistent file:

// using (StreamReader reader = File.OpenText(@"..\..\BookList.xml"))  using (StreamReader reader = File.OpenText(@"..\..\BadFileName.xml"))

Run the program by pressing F5. The code will break on the line you've changed, and the Exception Assistant will come forward, as shown in Figure 2-22.

Figure 2-22. The Exception Assistant

At this point, you can click one of the Troubleshooting Tips to open the appropriate Help file page, or you can click View Detail.

In this case, the problem is self-evident; the file could not be found, and your job is only to figure out why the OpenText method could not find your file.

2.8.2. What about...

...the View Detail link? What is that for?

Clicking the View Detail link will open the View Detail dialog box, as shown in Figure 2-23.

Figure 2-23. The View Detail dialog box

The details in this particular case are not very helpful because the exception is self-explanatory, but for some types of head-banging exceptions, the Exception Snapshot panel of the View Detail window can provide the information you need.

2.8.3. Where can I learn more?

C# Corner has a good article on exception handling at http://www.c-sharpcorner.com/Tutorials/ExceptionHandling101RVS.asp, as does O'Reilly's ONDotnet.com site at http://www.ondotnet.com/pub/a/dotnet.2001.09/04/error_handling.html.