AN OVERVIEW OF .NET ERROR HANDLING in Font

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Note This option doesn t exist in the Express editions, so if you are using one of those versions, then you

1. When you completed Exercise 4-2, your project was complied into an .exe file. This file can be found in the bin folder where your project was saved. Copy the MileageCalculator.exe file from the bin folder of Exercise 4-2 and place it on your desktop. 2. Double-click the .exe file to start the application. Once it displays, put 0 in the Gallons textbox. Press the btnGetMileage button and verify that the JIT Debug dialog box pops up (again, see Figure 4-22). 3. Click the Details button and review what kinds of information are given to you. 4. Scroll down to the end of the message. At the end, you ll see that this section looks like the following: ************** JIT Debugging **************

Read it carefully, as it explains some of what you need to do to set JIT debugging to use Visual Studio .NET.

5. Open your Solution from Exercise 4-2 using Visual Studio. Select Tools Options. 6. On the left-hand side of the Options dialog box, expand the Debugging option. If you don t see this option, then look at the bottom of the Options window for the Show All Settings check box and check the box.

7. In the Debugging folder, select the Just-In-Time page. If you do not see this, then you are most likely using the Express edition. This will not impact the rest of this chapter, but if you are using an Express edition, then this completes the exercise. 8. You should see the Enable Just-In-Time Debugging of These Types of Code box. Select the program types you want to debug: Managed, Native, or Script (to debug an ASP.NET application, you would choose both Script and Managed). Click OK. 9. When you are working with Windows Forms, you will need to enable Just-In-Time debugging in the machine.config file.

You will find the machine.config. file in one of the following folders:

C:\WINNT\Microsoft.NET\Framework\v2.0.50727\CONFIG or C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\CONFIG

Note The machine.config file is used to control the way .NET programs run on a particular computer. You will find this file in a subfolder of the C:\WINDOWS\Microsoft.NET\Framework or C:\WINNT\Microsoft.NET\ Framework folders of your hard drive (where C:\ is the drive your operating system is installed on). The actual file you need will be inside a subfolder with a version number as its name. For example, if the application you are trying to configure was written in .NET 2003, you would use this path: C:\WINDOWS\Microsoft.NET\ Framework\v1.1.4322. The newer versions of .NET will start with 2.0. At the time of this writing, the latest version was C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727. If you are unsure which version you used for the previous exercises, just use the latest version you can find and that will likely be the correct one.

10. Open the file called machine.config.Comments with a text editor, such as Notepad or Visual Studio. This file explains the settings available in the actual machine.config file. You will use this to add a new setting to the machine.config file without having to type out the new setting by hand. In the Comments version of the file, search for system.windows.forms jitDebugging=. What you should see is a set of XML tags like the following: <!-<system.windows.forms jitDebugging = "false" [true|false] /> --> <system.windows.forms jitDebugging="false" />

The <!-- and --> indicate an XML comment; whatever is inside of these tags is ignored. That being the case, what you are seeing inside of this comment is the syntax example for the statement below the comment. This example details the default setting, false, and the optional settings, [true|false]. Note that XML is case sensitive, so you must be sure to use lowercase when setting these options. 11. Copy the line of code that looks like this: <system.windows.forms jitDebugging="false" />. Now open the actual machine.config file in the same folder. 12. Paste the code you copied at the bottom of the file and change the setting from false to true, as shown here: <system.windows.forms jitDebugging="true" /> </configuration> 13. Save the machine.config file and close both documents. Open the MileageCalculator program again and test the Divide by Zero error again. Now when an error occurs, a different dialog box opens one which allows you to debug the program (see Figure 4-23).

Figure 4-23. Debug screen when JIT debugging is on 14. Press the Debug button and you will be presented with a list of debugging tools to choose from (see Figure 4-24). From here, you can choose either Visual Studio or the Common Language Runtime (CLR) debuggers. If you choose CLR, you will see a tool that looks and acts much like Visual Studio. Choose that one now and a new message box opens with a Break, Continue, and Ignore button. Click Continue to stop the program (we know, that is not very intuitive).