Build Your Own ASP.NET 2.0 Web Site Using C# & VB, Second Edition

All these commands are also available from the Debug toolbar, which is shown

in Figure 5.52.

Figure 5.52. The Debug toolbar

This toolbar appears by default when you’re debugging, but if it doesn’t, you can

make it display by right-clicking the toolbar and selecting Debug. The Debug

toolbar reflects the commands you can find in the Debug menu, which is depicted

in Figure 5.53, and the button on the extreme right gives you easy access to the

various debugging windows.

Figure 5.53. Debugging windows accessible from the toolbar

Other Kinds of Errors

Along with the runtime errors we’ve seen so far, ASP.NET can also throw the

following kinds of errors:

configuration errors

These are caused by problems in the Web.config

file. Try adding an incorrect tag to Web.config, and

the next time you try to load the application, an

error will occur.

parser errors

Parser errors are caused by the use of incorrect syn-

tax in an ASP.NET script page; for instance, prob-

lems in the definitions of ASP.NET controls in-

cluded in a web form will cause parser errors.

compilation errors

These errors are raised by the compiler when there’s

a syntax error in the page’s C# or VB code, and will

be caught by Visual Web Developer.

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Chapter 5: Building Web Applications

If you try to execute a page that contains compilation errors with Visual Web

Developer, those errors will be signaled right away, and the page won’t be loaded

in the web browser (see Figure 5.54).

Figure 5.54. Visual Web Developer warns about a compilation

error

If you’d like to try this for yourself, write some VB code, but terminate one of

the lines with a semicolon as if you were writing C# code, as shown in the snippet

below.

Visual Basic

Sub Page_Load(s As Object, e As EventArgs)

timeLabel.Text = DateTime.Now.ToString();

End Sub

If you try to run this code, Visual Web Developer will present you with the

message shown in Figure 5.54. If you choose Yes, a previous version of the code

that used to compile successfully will be executed. Usually, this isn’t what you

want: you’ll prefer to investigate the problem and fix the error. If you choose No,

Visual Web Developer will display a window called Error List. Double-click the

entry in the Error List, and the offending portion of code will be highlighted in

the editor. Moreover, hovering your cursor over the highlighted code will display

a tooltip containing a few details about the error, as Figure 5.55 illustrates.

After such a demonstration, I hope you agree that Visual Web Developer is a

fantastic tool. What you’ve just seen is merely a common-sense feature in the

world of Visual Web Developer, though—much more exciting and powerful fea-

tures are available!

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Other Kinds of Errors